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Xingyu.Wang
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commit
ffe91ea8ce
@ -1,978 +0,0 @@
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[#]: collector: (oska874)
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[#]: translator: (gxlct008)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Go on very small hardware (Part 2))
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[#]: via: (https://ziutek.github.io/2018/04/14/go_on_very_small_hardware2.html)
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[#]: author: (Michał Derkacz https://ziutek.github.io/)
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Go on very small hardware (Part 2)
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============================================================
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[][1]
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At the end of the [first part][2] of this article I promised to write something about _interfaces_ . I don’t want to write here a complete or even brief lecture about the interfaces. Instead, I’ll show a simple example how to define and use an interface, and then, how to take advantage of ubiquitous _io.Writer_ interface. There will also be a few words about _reflection_ and _semihosting_ .
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Interfaces are a crucial part of Go language. If you want to learn more about them, I suggest to read [Effective Go][3] and [Russ Cox article][4].
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### Concurrent Blinky – revisited
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When you read the code of previous examples you probably noticed a counterintuitive way to turn the LED on or off. The _Set_ method was used to turn the LED off and the _Clear_ method was used to turn the LED on. This is due to driving the LEDs in open-drain configuration. What we can do to make the code less confusing? Let’s define the _LED_ type with _On_ and _Off_ methods:
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```
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type LED struct {
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pin gpio.Pin
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}
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func (led LED) On() {
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led.pin.Clear()
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}
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func (led LED) Off() {
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led.pin.Set()
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}
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```
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Now we can simply call `led.On()` and `led.Off()` which no longer raises any doubts.
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In all previous examples I tried to use the same open-drain configuration to don’t complicate the code. But in the last example, it would be easier for me to connect the third LED between GND and PA3 pins and configure PA3 in push-pull mode. The next example will use a LED connected this way.
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But our new _LED_ type doesn’t support the push-pull configuration. In fact, we should call it _OpenDrainLED_ and define another _PushPullLED_ type:
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```
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type PushPullLED struct {
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pin gpio.Pin
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}
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func (led PushPullLED) On() {
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led.pin.Set()
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}
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func (led PushPullLED) Off() {
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led.pin.Clear()
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}
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```
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Note, that both types have the same methods that work the same. It would be nice if the code that operates on LEDs could use both types, without paying attention to which one it uses at the moment. The _interface type_ comes to help:
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```
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package main
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import (
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"delay"
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"stm32/hal/gpio"
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"stm32/hal/system"
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"stm32/hal/system/timer/systick"
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)
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type LED interface {
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On()
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Off()
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}
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type PushPullLED struct{ pin gpio.Pin }
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func (led PushPullLED) On() {
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led.pin.Set()
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}
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func (led PushPullLED) Off() {
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led.pin.Clear()
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}
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func MakePushPullLED(pin gpio.Pin) PushPullLED {
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pin.Setup(&gpio.Config{Mode: gpio.Out, Driver: gpio.PushPull})
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return PushPullLED{pin}
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}
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type OpenDrainLED struct{ pin gpio.Pin }
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func (led OpenDrainLED) On() {
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led.pin.Clear()
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}
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func (led OpenDrainLED) Off() {
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led.pin.Set()
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}
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func MakeOpenDrainLED(pin gpio.Pin) OpenDrainLED {
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pin.Setup(&gpio.Config{Mode: gpio.Out, Driver: gpio.OpenDrain})
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return OpenDrainLED{pin}
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}
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var led1, led2 LED
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func init() {
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system.SetupPLL(8, 1, 48/8)
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systick.Setup(2e6)
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gpio.A.EnableClock(false)
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led1 = MakeOpenDrainLED(gpio.A.Pin(4))
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led2 = MakePushPullLED(gpio.A.Pin(3))
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}
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func blinky(led LED, period int) {
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for {
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led.On()
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delay.Millisec(100)
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led.Off()
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delay.Millisec(period - 100)
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}
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}
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func main() {
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go blinky(led1, 500)
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blinky(led2, 1000)
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}
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```
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We’ve defined _LED_ interface that has two methods: _On_ and _Off_ . The _PushPullLED_ and _OpenDrainLED_ types represent two ways of driving LEDs. We also defined two _Make_ _*LED_ functions which act as constructors. Both types implement the _LED_ interface, so the values of these types can be assigned to the variables of type _LED_ :
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```
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led1 = MakeOpenDrainLED(gpio.A.Pin(4))
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led2 = MakePushPullLED(gpio.A.Pin(3))
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```
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In this case the assignability is checked at compile time. After the assignment the _led1_ variable contains `OpenDrainLED{gpio.A.Pin(4)}` and a pointer to the method set of the _OpenDrainLED_ type. The `led1.On()` call roughly corresponds to the following C code:
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```
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led1.methods->On(led1.value)
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```
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As you can see, this is quite inexpensive abstraction if only consider the function call overhead.
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But any assigment to an interface causes to include a lot of information about the assigned type. There can be a lot information in case of complex type which consists of many other types:
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```
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$ egc
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$ arm-none-eabi-size cortexm0.elf
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text data bss dec hex filename
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10356 196 212 10764 2a0c cortexm0.elf
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```
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If we don’t use [reflection][5] we can save some bytes by avoid to include the names of types and struct fields:
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```
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$ egc -nf -nt
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$ arm-none-eabi-size cortexm0.elf
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text data bss dec hex filename
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10312 196 212 10720 29e0 cortexm0.elf
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```
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The resulted binary still contains some necessary information about types and full information about all exported methods (with names). This information is need for checking assignability at runtime, mainly when you assign one value stored in the interface variable to any other variable.
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We can also remove type and field names from imported packages by recompiling them all:
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```
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$ cd $HOME/emgo
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$ ./clean.sh
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$ cd $HOME/firstemgo
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$ egc -nf -nt
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$ arm-none-eabi-size cortexm0.elf
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text data bss dec hex filename
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10272 196 212 10680 29b8 cortexm0.elf
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```
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Let’s load this program to see does it work as expected. This time we’ll use the [st-flash][6] command:
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```
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$ arm-none-eabi-objcopy -O binary cortexm0.elf cortexm0.bin
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$ st-flash write cortexm0.bin 0x8000000
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st-flash 1.4.0-33-gd76e3c7
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2018-04-10T22:04:34 INFO usb.c: -- exit_dfu_mode
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2018-04-10T22:04:34 INFO common.c: Loading device parameters....
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2018-04-10T22:04:34 INFO common.c: Device connected is: F0 small device, id 0x10006444
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2018-04-10T22:04:34 INFO common.c: SRAM size: 0x1000 bytes (4 KiB), Flash: 0x4000 bytes (16 KiB) in pages of 1024 bytes
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2018-04-10T22:04:34 INFO common.c: Attempting to write 10468 (0x28e4) bytes to stm32 address: 134217728 (0x8000000)
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Flash page at addr: 0x08002800 erased
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2018-04-10T22:04:34 INFO common.c: Finished erasing 11 pages of 1024 (0x400) bytes
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2018-04-10T22:04:34 INFO common.c: Starting Flash write for VL/F0/F3/F1_XL core id
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2018-04-10T22:04:34 INFO flash_loader.c: Successfully loaded flash loader in sram
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11/11 pages written
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2018-04-10T22:04:35 INFO common.c: Starting verification of write complete
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2018-04-10T22:04:35 INFO common.c: Flash written and verified! jolly good!
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```
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I didn’t connected the NRST signal to the programmer so the _—reset_ option can’t be used and the reset button have to be pressed to run the program.
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It seems that the _st-flash_ works a bit unreliably with this board (often requires reseting the ST-LINK dongle). Additionally, the current version doesn’t issue the reset command over SWD (uses only NRST signal). The software reset isn’t realiable however it usually works and lack of it introduces inconvenience. For this board-programmer pair the _OpenOCD_ works much better.
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### UART
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UART (Universal Aynchronous Receiver-Transmitter) is still one of the most important peripherals of today’s microcontrollers. Its advantage is unique combination of the following properties:
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* relatively high speed,
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* only two signal lines (even one in case of half-duplex communication),
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* symmetry of roles,
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* synchronous in-band signaling about new data (start bit),
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* accurate timing inside transmitted word.
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This causes that UART, originally intedned to transmit asynchronous messages consisting of 7-9 bit words, is also used to efficiently implement various other phisical protocols such as used by [WS28xx LEDs][7] or [1-wire][8] devices.
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However, we will use the UART in its usual role: to printing text messages from our program.
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```
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package main
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import (
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"io"
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"rtos"
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"stm32/hal/dma"
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"stm32/hal/gpio"
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"stm32/hal/irq"
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"stm32/hal/system"
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"stm32/hal/system/timer/systick"
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"stm32/hal/usart"
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)
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var tts *usart.Driver
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func init() {
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system.SetupPLL(8, 1, 48/8)
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systick.Setup(2e6)
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gpio.A.EnableClock(true)
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tx := gpio.A.Pin(9)
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tx.Setup(&gpio.Config{Mode: gpio.Alt})
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tx.SetAltFunc(gpio.USART1_AF1)
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d := dma.DMA1
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d.EnableClock(true)
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tts = usart.NewDriver(usart.USART1, d.Channel(2, 0), nil, nil)
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tts.Periph().EnableClock(true)
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tts.Periph().SetBaudRate(115200)
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tts.Periph().Enable()
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tts.EnableTx()
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rtos.IRQ(irq.USART1).Enable()
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rtos.IRQ(irq.DMA1_Channel2_3).Enable()
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}
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func main() {
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io.WriteString(tts, "Hello, World!\r\n")
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}
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func ttsISR() {
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tts.ISR()
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}
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func ttsDMAISR() {
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tts.TxDMAISR()
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}
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//c:__attribute__((section(".ISRs")))
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var ISRs = [...]func(){
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irq.USART1: ttsISR,
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irq.DMA1_Channel2_3: ttsDMAISR,
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}
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```
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You can find this code slightly complicated but for now there is no simpler UART driver in STM32 HAL (simple polling driver will be probably useful in some cases). The _usart.Driver_ is efficient driver that uses DMA and interrupts to ofload the CPU.
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|
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STM32 USART peripheral provides traditional UART and its synchronous version. To use it as output we have to connect its Tx signal to the right GPIO pin:
|
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```
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tx.Setup(&gpio.Config{Mode: gpio.Alt})
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tx.SetAltFunc(gpio.USART1_AF1)
|
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|
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```
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|
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The _usart.Driver_ is configured in Tx-only mode (rxdma and rxbuf are set to nil):
|
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|
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```
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tts = usart.NewDriver(usart.USART1, d.Channel(2, 0), nil, nil)
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```
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We use its _WriteString_ method to print the famous sentence. Let’s clean everything and compile this program:
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|
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```
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$ cd $HOME/emgo
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$ ./clean.sh
|
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$ cd $HOME/firstemgo
|
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$ egc
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$ arm-none-eabi-size cortexm0.elf
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text data bss dec hex filename
|
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12728 236 176 13140 3354 cortexm0.elf
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|
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```
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|
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To see something you need an UART peripheral in your PC.
|
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|
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**Do not use RS232 port or USB to RS232 converter!**
|
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|
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The STM32 family uses 3.3 V logic but RS232 can produce from -15 V to +15 V which will probably demage your MCU. You need USB to UART converter that uses 3.3 V logic. Popular converters are based on FT232 or CP2102 chips.
|
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|
||||
|
||||
|
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You also need some terminal emulator program (I prefer [picocom][9]). Flash the new image, run the terminal emulator and press the reset button a few times:
|
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|
||||
```
|
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$ openocd -d0 -f interface/stlink.cfg -f target/stm32f0x.cfg -c 'init; program cortexm0.elf; reset run; exit'
|
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Open On-Chip Debugger 0.10.0+dev-00319-g8f1f912a (2018-03-07-19:20)
|
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Licensed under GNU GPL v2
|
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For bug reports, read
|
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http://openocd.org/doc/doxygen/bugs.html
|
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debug_level: 0
|
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adapter speed: 1000 kHz
|
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adapter_nsrst_delay: 100
|
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none separate
|
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adapter speed: 950 kHz
|
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target halted due to debug-request, current mode: Thread
|
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xPSR: 0xc1000000 pc: 0x080016f4 msp: 0x20000a20
|
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adapter speed: 4000 kHz
|
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** Programming Started **
|
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auto erase enabled
|
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target halted due to breakpoint, current mode: Thread
|
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xPSR: 0x61000000 pc: 0x2000003a msp: 0x20000a20
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wrote 13312 bytes from file cortexm0.elf in 1.020185s (12.743 KiB/s)
|
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** Programming Finished **
|
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adapter speed: 950 kHz
|
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$
|
||||
$ picocom -b 115200 /dev/ttyUSB0
|
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picocom v3.1
|
||||
|
||||
port is : /dev/ttyUSB0
|
||||
flowcontrol : none
|
||||
baudrate is : 115200
|
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parity is : none
|
||||
databits are : 8
|
||||
stopbits are : 1
|
||||
escape is : C-a
|
||||
local echo is : no
|
||||
noinit is : no
|
||||
noreset is : no
|
||||
hangup is : no
|
||||
nolock is : no
|
||||
send_cmd is : sz -vv
|
||||
receive_cmd is : rz -vv -E
|
||||
imap is :
|
||||
omap is :
|
||||
emap is : crcrlf,delbs,
|
||||
logfile is : none
|
||||
initstring : none
|
||||
exit_after is : not set
|
||||
exit is : no
|
||||
|
||||
Type [C-a] [C-h] to see available commands
|
||||
Terminal ready
|
||||
Hello, World!
|
||||
Hello, World!
|
||||
Hello, World!
|
||||
|
||||
```
|
||||
|
||||
Every press of the reset button produces new “Hello, World!” line. Everything works as expected.
|
||||
|
||||
To see bi-directional UART code for this MCU check out [this example][10].
|
||||
|
||||
### io.Writer
|
||||
|
||||
The _io.Writer_ interface is probably the second most commonly used interface type in Go, right after the _error_ interface. Its definition looks like this:
|
||||
|
||||
```
|
||||
type Writer interface {
|
||||
Write(p []byte) (n int, err error)
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
_usart.Driver_ implements _io.Writer_ so we can replace:
|
||||
|
||||
```
|
||||
tts.WriteString("Hello, World!\r\n")
|
||||
|
||||
```
|
||||
|
||||
with
|
||||
|
||||
```
|
||||
io.WriteString(tts, "Hello, World!\r\n")
|
||||
|
||||
```
|
||||
|
||||
Additionally you need to add the _io_ package to the _import_ section.
|
||||
|
||||
The declaration of _io.WriteString_ function looks as follows:
|
||||
|
||||
```
|
||||
func WriteString(w Writer, s string) (n int, err error)
|
||||
|
||||
```
|
||||
|
||||
As you can see, the _io.WriteString_ allows to write strings using any type that implements _io.Writer_ interface. Internally it check does the underlying type has _WriteString_ method and uses it instead of _Write_ if available.
|
||||
|
||||
Let’s compile the modified program:
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
15456 320 248 16024 3e98 cortexm0.elf
|
||||
|
||||
```
|
||||
|
||||
As you can see, _io.WriteString_ causes a significant increase in the size of the binary: 15776 - 12964 = 2812 bytes. There isn’t too much space left on the Flash. What caused such a drastic increase in size?
|
||||
|
||||
Using the command:
|
||||
|
||||
```
|
||||
arm-none-eabi-nm --print-size --size-sort --radix=d cortexm0.elf
|
||||
|
||||
```
|
||||
|
||||
we can print all symbols ordered by its size for both cases. By filtering and analyzing the obtained data (awk, diff) we can find about 80 new symbols. The ten largest are:
|
||||
|
||||
```
|
||||
> 00000062 T stm32$hal$usart$Driver$DisableRx
|
||||
> 00000072 T stm32$hal$usart$Driver$RxDMAISR
|
||||
> 00000076 T internal$Type$Implements
|
||||
> 00000080 T stm32$hal$usart$Driver$EnableRx
|
||||
> 00000084 t errors$New
|
||||
> 00000096 R $8$stm32$hal$usart$Driver$$
|
||||
> 00000100 T stm32$hal$usart$Error$Error
|
||||
> 00000360 T io$WriteString
|
||||
> 00000660 T stm32$hal$usart$Driver$Read
|
||||
|
||||
```
|
||||
|
||||
So, even though we don’t use the _usart.Driver.Read_ method it was compiled in, same as _DisableRx_ , _RxDMAISR_ , _EnableRx_ and other not mentioned above. Unfortunately, if you assign something to the interface, its full method set is required (with all dependences). This isn’t a problem for a large programs that use most of the methods anyway. But for our simple one it’s a huge burden.
|
||||
|
||||
We’re already close to the limits of our MCU but let’s try to print some numbers (you need to replace _io_ package with _strconv_ in _import_ section):
|
||||
|
||||
```
|
||||
func main() {
|
||||
a := 12
|
||||
b := -123
|
||||
|
||||
tts.WriteString("a = ")
|
||||
strconv.WriteInt(tts, a, 10, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
tts.WriteString("b = ")
|
||||
strconv.WriteInt(tts, b, 10, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
|
||||
tts.WriteString("hex(a) = ")
|
||||
strconv.WriteInt(tts, a, 16, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
tts.WriteString("hex(b) = ")
|
||||
strconv.WriteInt(tts, b, 16, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
As in the case of _io.WriteString_ function, the first argument of the _strconv.WriteInt_ is of type _io.Writer_ .
|
||||
|
||||
```
|
||||
$ egc
|
||||
/usr/local/arm/bin/arm-none-eabi-ld: /home/michal/firstemgo/cortexm0.elf section `.rodata' will not fit in region `Flash'
|
||||
/usr/local/arm/bin/arm-none-eabi-ld: region `Flash' overflowed by 692 bytes
|
||||
exit status 1
|
||||
|
||||
```
|
||||
|
||||
This time we’ve run out of space. Let’s try to slim down the information about types:
|
||||
|
||||
```
|
||||
$ cd $HOME/emgo
|
||||
$ ./clean.sh
|
||||
$ cd $HOME/firstemgo
|
||||
$ egc -nf -nt
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
15876 316 320 16512 4080 cortexm0.elf
|
||||
|
||||
```
|
||||
|
||||
It was close, but we fit. Let’s load and run this code:
|
||||
|
||||
```
|
||||
a = 12
|
||||
b = -123
|
||||
hex(a) = c
|
||||
hex(b) = -7b
|
||||
|
||||
```
|
||||
|
||||
The _strconv_ package in Emgo is quite different from its archetype in Go. It is intended for direct use to write formatted numbers and in many cases can replace heavy _fmt_ package. That’s why the function names start with _Write_ instead of _Format_ and have additional two parameters. Below is an example of their use:
|
||||
|
||||
```
|
||||
func main() {
|
||||
b := -123
|
||||
strconv.WriteInt(tts, b, 10, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, 6, ' ')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, 6, '0')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, 6, '.')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, -6, ' ')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, -6, '0')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, -6, '.')
|
||||
tts.WriteString("\r\n")
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
There is its output:
|
||||
|
||||
```
|
||||
-123
|
||||
-123
|
||||
-00123
|
||||
..-123
|
||||
-123
|
||||
-123
|
||||
-123..
|
||||
|
||||
```
|
||||
|
||||
### Unix streams and Morse code
|
||||
|
||||
Thanks to the fact that most of the functions that write something use _io.Writer_ instead of concrete type (eg. _FILE_ in C) we get a functionality similar to _Unix streams_ . In Unix we can easily combine simple commands to perform larger tasks. For example, we can write text to the file this way:
|
||||
|
||||
```
|
||||
echo "Hello, World!" > file.txt
|
||||
|
||||
```
|
||||
|
||||
The `>` operator writes the output stream of the preceding command to the file. There is also `|`operator that connects output and input streams of adjacent commands.
|
||||
|
||||
Thanks to the streams we can easily convert/filter output of any command. For example, to convert all letters to uppercase we can filter the echo’s output through _tr_ command:
|
||||
|
||||
```
|
||||
echo "Hello, World!" | tr a-z A-Z > file.txt
|
||||
|
||||
```
|
||||
|
||||
To show the analogy between _io.Writer_ and Unix streams let’s write our:
|
||||
|
||||
```
|
||||
io.WriteString(tts, "Hello, World!\r\n")
|
||||
|
||||
```
|
||||
|
||||
in the following pseudo-unix form:
|
||||
|
||||
```
|
||||
io.WriteString "Hello, World!" | usart.Driver usart.USART1
|
||||
|
||||
```
|
||||
|
||||
The next example will show how to do this:
|
||||
|
||||
```
|
||||
io.WriteString "Hello, World!" | MorseWriter | usart.Driver usart.USART1
|
||||
|
||||
```
|
||||
|
||||
Let’s create a simple encoder that encodes the text written to it using Morse coding:
|
||||
|
||||
```
|
||||
type MorseWriter struct {
|
||||
W io.Writer
|
||||
}
|
||||
|
||||
func (w *MorseWriter) Write(s []byte) (int, error) {
|
||||
var buf [8]byte
|
||||
for n, c := range s {
|
||||
switch {
|
||||
case c == '\n':
|
||||
c = ' ' // Replace new lines with spaces.
|
||||
case 'a' <= c && c <= 'z':
|
||||
c -= 'a' - 'A' // Convert to upper case.
|
||||
}
|
||||
if c < ' ' || 'Z' < c {
|
||||
continue // c is outside ASCII [' ', 'Z']
|
||||
}
|
||||
var symbol morseSymbol
|
||||
if c == ' ' {
|
||||
symbol.length = 1
|
||||
buf[0] = ' '
|
||||
} else {
|
||||
symbol = morseSymbols[c-'!']
|
||||
for i := uint(0); i < uint(symbol.length); i++ {
|
||||
if (symbol.code>>i)&1 != 0 {
|
||||
buf[i] = '-'
|
||||
} else {
|
||||
buf[i] = '.'
|
||||
}
|
||||
}
|
||||
}
|
||||
buf[symbol.length] = ' '
|
||||
if _, err := w.W.Write(buf[:symbol.length+1]); err != nil {
|
||||
return n, err
|
||||
}
|
||||
}
|
||||
return len(s), nil
|
||||
}
|
||||
|
||||
type morseSymbol struct {
|
||||
code, length byte
|
||||
}
|
||||
|
||||
//emgo:const
|
||||
var morseSymbols = [...]morseSymbol{
|
||||
{1<<0 | 1<<1 | 1<<2, 4}, // ! ---.
|
||||
{1<<1 | 1<<4, 6}, // " .-..-.
|
||||
{}, // #
|
||||
{1<<3 | 1<<6, 7}, // $ ...-..-
|
||||
|
||||
// Some code omitted...
|
||||
|
||||
{1<<0 | 1<<3, 4}, // X -..-
|
||||
{1<<0 | 1<<2 | 1<<3, 4}, // Y -.--
|
||||
{1<<0 | 1<<1, 4}, // Z --..
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
You can find the full _morseSymbols_ array [here][11]. The `//emgo:const` directive ensures that _morseSymbols_ array won’t be copied to the RAM.
|
||||
|
||||
Now we can print our sentence in two ways:
|
||||
|
||||
```
|
||||
func main() {
|
||||
s := "Hello, World!\r\n"
|
||||
mw := &MorseWriter{tts}
|
||||
|
||||
io.WriteString(tts, s)
|
||||
io.WriteString(mw, s)
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
We use the pointer to the _MorseWriter_ `&MorseWriter{tts}` instead os simple `MorseWriter{tts}` value beacuse the _MorseWriter_ is to big to fit into an interface variable.
|
||||
|
||||
Emgo, unlike Go, doesn’t dynamically allocate memory for value stored in interface variable. The interface type has limited size, equal to the size of three pointers (to fit _slice_ ) or two _float64_ (to fit _complex128_ ), what is bigger. It can directly store values of all basic types and small structs/arrays but for bigger values you must use pointers.
|
||||
|
||||
Let’s compile this code and see its output:
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
15152 324 248 15724 3d6c cortexm0.elf
|
||||
|
||||
```
|
||||
|
||||
```
|
||||
Hello, World!
|
||||
.... . .-.. .-.. --- --..-- .-- --- .-. .-.. -.. ---.
|
||||
|
||||
```
|
||||
|
||||
### The Ultimate Blinky
|
||||
|
||||
The _Blinky_ is hardware equivalent of _Hello, World!_ program. Once we have a Morse encoder we can easly combine both to obtain the _Ultimate Blinky_ program:
|
||||
|
||||
```
|
||||
package main
|
||||
|
||||
import (
|
||||
"delay"
|
||||
"io"
|
||||
|
||||
"stm32/hal/gpio"
|
||||
"stm32/hal/system"
|
||||
"stm32/hal/system/timer/systick"
|
||||
)
|
||||
|
||||
var led gpio.Pin
|
||||
|
||||
func init() {
|
||||
system.SetupPLL(8, 1, 48/8)
|
||||
systick.Setup(2e6)
|
||||
|
||||
gpio.A.EnableClock(false)
|
||||
led = gpio.A.Pin(4)
|
||||
|
||||
cfg := gpio.Config{Mode: gpio.Out, Driver: gpio.OpenDrain, Speed: gpio.Low}
|
||||
led.Setup(&cfg)
|
||||
}
|
||||
|
||||
type Telegraph struct {
|
||||
Pin gpio.Pin
|
||||
Dotms int // Dot length [ms]
|
||||
}
|
||||
|
||||
func (t Telegraph) Write(s []byte) (int, error) {
|
||||
for _, c := range s {
|
||||
switch c {
|
||||
case '.':
|
||||
t.Pin.Clear()
|
||||
delay.Millisec(t.Dotms)
|
||||
t.Pin.Set()
|
||||
delay.Millisec(t.Dotms)
|
||||
case '-':
|
||||
t.Pin.Clear()
|
||||
delay.Millisec(3 * t.Dotms)
|
||||
t.Pin.Set()
|
||||
delay.Millisec(t.Dotms)
|
||||
case ' ':
|
||||
delay.Millisec(3 * t.Dotms)
|
||||
}
|
||||
}
|
||||
return len(s), nil
|
||||
}
|
||||
|
||||
func main() {
|
||||
telegraph := &MorseWriter{Telegraph{led, 100}}
|
||||
for {
|
||||
io.WriteString(telegraph, "Hello, World! ")
|
||||
}
|
||||
}
|
||||
|
||||
// Some code omitted...
|
||||
|
||||
```
|
||||
|
||||
In the above example I omitted the definition of _MorseWriter_ type because it was shown earlier. The full version is available [here][12]. Let’s compile it and run:
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
11772 244 244 12260 2fe4 cortexm0.elf
|
||||
|
||||
```
|
||||
|
||||
|
||||
|
||||
### Reflection
|
||||
|
||||
Yes, Emgo supports [reflection][13]. The _reflect_ package isn’t complete yet but that what is done is enough to implement _fmt.Print_ family of functions. Let’s see what can we do on our small MCU.
|
||||
|
||||
To reduce memory usage we will use [semihosting][14] as standard output. For convenience, we also write simple _println_ function which to some extent mimics _fmt.Println_ .
|
||||
|
||||
```
|
||||
package main
|
||||
|
||||
import (
|
||||
"debug/semihosting"
|
||||
"reflect"
|
||||
"strconv"
|
||||
|
||||
"stm32/hal/system"
|
||||
"stm32/hal/system/timer/systick"
|
||||
)
|
||||
|
||||
var stdout semihosting.File
|
||||
|
||||
func init() {
|
||||
system.SetupPLL(8, 1, 48/8)
|
||||
systick.Setup(2e6)
|
||||
|
||||
var err error
|
||||
stdout, err = semihosting.OpenFile(":tt", semihosting.W)
|
||||
for err != nil {
|
||||
}
|
||||
}
|
||||
|
||||
type stringer interface {
|
||||
String() string
|
||||
}
|
||||
|
||||
func println(args ...interface{}) {
|
||||
for i, a := range args {
|
||||
if i > 0 {
|
||||
stdout.WriteString(" ")
|
||||
}
|
||||
switch v := a.(type) {
|
||||
case string:
|
||||
stdout.WriteString(v)
|
||||
case int:
|
||||
strconv.WriteInt(stdout, v, 10, 0, 0)
|
||||
case bool:
|
||||
strconv.WriteBool(stdout, v, 't', 0, 0)
|
||||
case stringer:
|
||||
stdout.WriteString(v.String())
|
||||
default:
|
||||
stdout.WriteString("%unknown")
|
||||
}
|
||||
}
|
||||
stdout.WriteString("\r\n")
|
||||
}
|
||||
|
||||
type S struct {
|
||||
A int
|
||||
B bool
|
||||
}
|
||||
|
||||
func main() {
|
||||
p := &S{-123, true}
|
||||
|
||||
v := reflect.ValueOf(p)
|
||||
|
||||
println("kind(p) =", v.Kind())
|
||||
println("kind(*p) =", v.Elem().Kind())
|
||||
println("type(*p) =", v.Elem().Type())
|
||||
|
||||
v = v.Elem()
|
||||
|
||||
println("*p = {")
|
||||
for i := 0; i < v.NumField(); i++ {
|
||||
ft := v.Type().Field(i)
|
||||
fv := v.Field(i)
|
||||
println(" ", ft.Name(), ":", fv.Interface())
|
||||
}
|
||||
println("}")
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
The _semihosting.OpenFile_ function allows to open/create file on the host side. The special path _:tt_ corresponds to host’s standard output.
|
||||
|
||||
The _println_ function accepts arbitrary number of arguments, each of arbitrary type:
|
||||
|
||||
```
|
||||
func println(args ...interface{})
|
||||
|
||||
```
|
||||
|
||||
It’s possible because any type implements the empty interface _interface{}_ . The _println_ uses [type switch][15] to print strings, integers and booleans:
|
||||
|
||||
```
|
||||
switch v := a.(type) {
|
||||
case string:
|
||||
stdout.WriteString(v)
|
||||
case int:
|
||||
strconv.WriteInt(stdout, v, 10, 0, 0)
|
||||
case bool:
|
||||
strconv.WriteBool(stdout, v, 't', 0, 0)
|
||||
case stringer:
|
||||
stdout.WriteString(v.String())
|
||||
default:
|
||||
stdout.WriteString("%unknown")
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Additionally it supports any type that implements _stringer_ interface, that is, any type that has _String()_ method. In any _case_ clause the _v_ variable has the right type, same as listed after _case_ keyword.
|
||||
|
||||
The `reflect.ValueOf(p)` returns _p_ in the form that allows to analyze its type and content programmatically. As you can see, we can even dereference pointers using `v.Elem()` and print all struct fields with their names.
|
||||
|
||||
Let’s try to compile this code. For now let’s see what will come out if compiled without type and field names:
|
||||
|
||||
```
|
||||
$ egc -nt -nf
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
16028 216 312 16556 40ac cortexm0.elf
|
||||
|
||||
```
|
||||
|
||||
Only 140 free bytes left on the Flash. Let’s load it using OpenOCD with semihosting enabled:
|
||||
|
||||
```
|
||||
$ openocd -d0 -f interface/stlink.cfg -f target/stm32f0x.cfg -c 'init; program cortexm0.elf; arm semihosting enable; reset run'
|
||||
Open On-Chip Debugger 0.10.0+dev-00319-g8f1f912a (2018-03-07-19:20)
|
||||
Licensed under GNU GPL v2
|
||||
For bug reports, read
|
||||
http://openocd.org/doc/doxygen/bugs.html
|
||||
debug_level: 0
|
||||
adapter speed: 1000 kHz
|
||||
adapter_nsrst_delay: 100
|
||||
none separate
|
||||
adapter speed: 950 kHz
|
||||
target halted due to debug-request, current mode: Thread
|
||||
xPSR: 0xc1000000 pc: 0x08002338 msp: 0x20000a20
|
||||
adapter speed: 4000 kHz
|
||||
** Programming Started **
|
||||
auto erase enabled
|
||||
target halted due to breakpoint, current mode: Thread
|
||||
xPSR: 0x61000000 pc: 0x2000003a msp: 0x20000a20
|
||||
wrote 16384 bytes from file cortexm0.elf in 0.700133s (22.853 KiB/s)
|
||||
** Programming Finished **
|
||||
semihosting is enabled
|
||||
adapter speed: 950 kHz
|
||||
kind(p) = ptr
|
||||
kind(*p) = struct
|
||||
type(*p) =
|
||||
*p = {
|
||||
X. : -123
|
||||
X. : true
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
If you’ve actually run this code, you noticed that semihosting is slow, especially if you write a byte after byte (buffering helps).
|
||||
|
||||
As you can see, there is no type name for `*p` and all struct fields have the same _X._ name. Let’s compile this program again, this time without _-nt -nf_ options:
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
16052 216 312 16580 40c4 cortexm0.elf
|
||||
|
||||
```
|
||||
|
||||
Now the type and field names have been included but only these defined in ~~_main.go_ file~~ _main_ package. The output of our program looks as follows:
|
||||
|
||||
```
|
||||
kind(p) = ptr
|
||||
kind(*p) = struct
|
||||
type(*p) = S
|
||||
*p = {
|
||||
A : -123
|
||||
B : true
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Reflection is a crucial part of any easy to use serialization library and serialization ~~algorithms~~ like [JSON][16]gain in importance in the IOT era.
|
||||
|
||||
This is where I finish the second part of this article. I think there is a chance for the third part, more entertaining, where we connect to this board various interesting devices. If this board won’t carry them, we replace it with something a little bigger.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://ziutek.github.io/2018/04/14/go_on_very_small_hardware2.html
|
||||
|
||||
作者：[Michał Derkacz ][a]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]:https://ziutek.github.io/
|
||||
[1]:https://ziutek.github.io/2018/04/14/go_on_very_small_hardware2.html
|
||||
[2]:https://ziutek.github.io/2018/03/30/go_on_very_small_hardware.html
|
||||
[3]:https://golang.org/doc/effective_go.html#interfaces
|
||||
[4]:https://research.swtch.com/interfaces
|
||||
[5]:https://blog.golang.org/laws-of-reflection
|
||||
[6]:https://github.com/texane/stlink
|
||||
[7]:http://www.world-semi.com/solution/list-4-1.html
|
||||
[8]:https://en.wikipedia.org/wiki/1-Wire
|
||||
[9]:https://github.com/npat-efault/picocom
|
||||
[10]:https://github.com/ziutek/emgo/blob/master/egpath/src/stm32/examples/f030-demo-board/usart/main.go
|
||||
[11]:https://github.com/ziutek/emgo/blob/master/egpath/src/stm32/examples/f030-demo-board/morseuart/main.go
|
||||
[12]:https://github.com/ziutek/emgo/blob/master/egpath/src/stm32/examples/f030-demo-board/morseled/main.go
|
||||
[13]:https://blog.golang.org/laws-of-reflection
|
||||
[14]:http://infocenter.arm.com/help/topic/com.arm.doc.dui0471g/Bgbjjgij.html
|
||||
[15]:https://golang.org/doc/effective_go.html#type_switch
|
||||
[16]:https://en.wikipedia.org/wiki/JSON
|
||||
947
translated/tech/20180414 Go on very small hardware Part 2.md
Normal file
947
translated/tech/20180414 Go on very small hardware Part 2.md
Normal file
@ -0,0 +1,947 @@
|
||||
[#]: collector: (oska874)
|
||||
[#]: translator: (gxlct008)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Go on very small hardware Part 2)
|
||||
[#]: via: (https://ziutek.github.io/2018/04/14/go_on_very_small_hardware2.html)
|
||||
[#]: author: (Michał Derkacz https://ziutek.github.io/)
|
||||
|
||||
Go 语言在极小硬件上的运用（二）
|
||||
============================================================
|
||||
|
||||
|
||||
[][1]
|
||||
|
||||
|
||||
在本文的 [第一部分][2] 的结尾，我承诺要写关于 _interfaces_ 的内容。我不想在这里写有关接口的完整甚至简短的讲义。相反，我将展示一个简单的示例，来说明如何定义和使用接口，以及如何利用无处不在的 _io.Writer_ 接口。还有一些关于 _reflection_ 和 _semihosting_ 的内容。
|
||||
|
||||
接口是 Go 语言的重要组成部分。如果您想了解更多有关它们的信息，我建议您阅读 [Effective Go][3] 和 [Russ Cox 的文章][4]。
|
||||
|
||||
### 并发 Blinky – 回顾
|
||||
|
||||
当您阅读前面示例的代码时，您可能会注意到一个违反直觉的方式来打开或关闭 LED。 _Set_ 方法用于关闭 LED，_Clear_ 方法用于打开 LED。这是由于在 <ruby>漏极开路配置<rt>open-drain configuration</rt></ruby> 下驱动了 LED。我们可以做些什么来减少代码的混乱？ 让我们用 _On_ 和 _Off_ 方法来定义 _LED_ 类型：
|
||||
|
||||
```
|
||||
type LED struct {
|
||||
pin gpio.Pin
|
||||
}
|
||||
|
||||
func (led LED) On() {
|
||||
led.pin.Clear()
|
||||
}
|
||||
|
||||
func (led LED) Off() {
|
||||
led.pin.Set()
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
现在我们可以简单地调用 `led.On()` 和 `led.Off()`，这不会再引起任何疑惑了。
|
||||
|
||||
|
||||
在前面的所有示例中，我都尝试使用相同的 <ruby>漏极开路配置<rt>open-drain configuration</rt></ruby>来 避免代码复杂化。但是在最后一个示例中，对于我来说，将第三个 LED 连接到 GND 和 PA3 引脚之间并将 PA3 配置为<ruby>推挽模式<rt>push-pull mode</rt></ruby>会更容易。下一个示例将使用以此方式连接的 LED。
|
||||
|
||||
但是我们的新 _LED_ 类型不支持推挽配置。实际上，我们应该将其称为 _OpenDrainLED_，并定义另一个类型 _PushPullLED_：
|
||||
|
||||
```
|
||||
type PushPullLED struct {
|
||||
pin gpio.Pin
|
||||
}
|
||||
|
||||
func (led PushPullLED) On() {
|
||||
led.pin.Set()
|
||||
}
|
||||
|
||||
func (led PushPullLED) Off() {
|
||||
led.pin.Clear()
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
请注意，这两种类型都具有相同的方法，它们的工作方式也相同。如果在 LED 上运行的代码可以同时使用这两种类型，而不必注意当前使用的是哪种类型，那就太好了。 _interface type_ 可以提供帮助：
|
||||
|
||||
```
|
||||
package main
|
||||
|
||||
import (
|
||||
"delay"
|
||||
|
||||
"stm32/hal/gpio"
|
||||
"stm32/hal/system"
|
||||
"stm32/hal/system/timer/systick"
|
||||
)
|
||||
|
||||
type LED interface {
|
||||
On()
|
||||
Off()
|
||||
}
|
||||
|
||||
type PushPullLED struct{ pin gpio.Pin }
|
||||
|
||||
func (led PushPullLED) On() {
|
||||
led.pin.Set()
|
||||
}
|
||||
|
||||
func (led PushPullLED) Off() {
|
||||
led.pin.Clear()
|
||||
}
|
||||
|
||||
func MakePushPullLED(pin gpio.Pin) PushPullLED {
|
||||
pin.Setup(&gpio.Config{Mode: gpio.Out, Driver: gpio.PushPull})
|
||||
return PushPullLED{pin}
|
||||
}
|
||||
|
||||
type OpenDrainLED struct{ pin gpio.Pin }
|
||||
|
||||
func (led OpenDrainLED) On() {
|
||||
led.pin.Clear()
|
||||
}
|
||||
|
||||
func (led OpenDrainLED) Off() {
|
||||
led.pin.Set()
|
||||
}
|
||||
|
||||
func MakeOpenDrainLED(pin gpio.Pin) OpenDrainLED {
|
||||
pin.Setup(&gpio.Config{Mode: gpio.Out, Driver: gpio.OpenDrain})
|
||||
return OpenDrainLED{pin}
|
||||
}
|
||||
|
||||
var led1, led2 LED
|
||||
|
||||
func init() {
|
||||
system.SetupPLL(8, 1, 48/8)
|
||||
systick.Setup(2e6)
|
||||
|
||||
gpio.A.EnableClock(false)
|
||||
led1 = MakeOpenDrainLED(gpio.A.Pin(4))
|
||||
led2 = MakePushPullLED(gpio.A.Pin(3))
|
||||
}
|
||||
|
||||
func blinky(led LED, period int) {
|
||||
for {
|
||||
led.On()
|
||||
delay.Millisec(100)
|
||||
led.Off()
|
||||
delay.Millisec(period - 100)
|
||||
}
|
||||
}
|
||||
|
||||
func main() {
|
||||
go blinky(led1, 500)
|
||||
blinky(led2, 1000)
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
我们定义了 _LED_ 接口，它有两个方法： _On_ 和 _Off_。 _PushPullLED_ 和 _OpenDrainLED_ 类型代表两种驱动 LED 的方式。我们还定义了两个用作构造函数的 _Make_ _*LED_ 函数。这两种类型都实现了 _LED_ 接口，因此可以将这些类型的值赋给 _LED_ 类型的变量：
|
||||
|
||||
```
|
||||
led1 = MakeOpenDrainLED(gpio.A.Pin(4))
|
||||
led2 = MakePushPullLED(gpio.A.Pin(3))
|
||||
```
|
||||
|
||||
在这种情况下，可赋值性在编译时检查。赋值后，_led1_ 变量包含一个 `OpenDrainLED{gpio.A.Pin(4)}`，以及一个指向 _OpenDainLED_ 类型的方法集的指针。 `led1.On()` 调用大致对应于以下 C 代码：
|
||||
|
||||
```
|
||||
led1.methods->On(led1.value)
|
||||
```
|
||||
|
||||
如您所见，如果仅考虑函数调用的开销，这是相当便宜的抽象。
|
||||
|
||||
|
||||
但是，对接口的任何赋值都会导致包含有关已赋值类型的大量信息。对于由许多其他类型组成的复杂类型，可能会有很多信息：
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
10356 196 212 10764 2a0c cortexm0.elf
|
||||
```
|
||||
|
||||
如果我们不使用 [反射][5]，可以通过避免包含类型和结构字段的名称来节省一些字节：
|
||||
|
||||
```
|
||||
$ egc -nf -nt
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
10312 196 212 10720 29e0 cortexm0.elf
|
||||
```
|
||||
|
||||
生成的二进制文件仍然包含一些有关类型的必要信息和关于所有导出方法（带有名称）的完整信息。在运行时，主要是当您将存储在接口变量中的一个值赋值给任何其他变量时，需要此信息来检查可赋值性。
|
||||
|
||||
我们还可以通过重新编译所导入的包来删除它们的类型和字段名称：
|
||||
|
||||
```
|
||||
$ cd $HOME/emgo
|
||||
$ ./clean.sh
|
||||
$ cd $HOME/firstemgo
|
||||
$ egc -nf -nt
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
10272 196 212 10680 29b8 cortexm0.elf
|
||||
```
|
||||
|
||||
让我们加载这个程序，看看它是否按预期工作。这一次我们将使用 [st-flash][6] 命令：
|
||||
|
||||
```
|
||||
$ arm-none-eabi-objcopy -O binary cortexm0.elf cortexm0.bin
|
||||
$ st-flash write cortexm0.bin 0x8000000
|
||||
st-flash 1.4.0-33-gd76e3c7
|
||||
2018-04-10T22:04:34 INFO usb.c: -- exit_dfu_mode
|
||||
2018-04-10T22:04:34 INFO common.c: Loading device parameters....
|
||||
2018-04-10T22:04:34 INFO common.c: Device connected is: F0 small device, id 0x10006444
|
||||
2018-04-10T22:04:34 INFO common.c: SRAM size: 0x1000 bytes (4 KiB), Flash: 0x4000 bytes (16 KiB) in pages of 1024 bytes
|
||||
2018-04-10T22:04:34 INFO common.c: Attempting to write 10468 (0x28e4) bytes to stm32 address: 134217728 (0x8000000)
|
||||
Flash page at addr: 0x08002800 erased
|
||||
2018-04-10T22:04:34 INFO common.c: Finished erasing 11 pages of 1024 (0x400) bytes
|
||||
2018-04-10T22:04:34 INFO common.c: Starting Flash write for VL/F0/F3/F1_XL core id
|
||||
2018-04-10T22:04:34 INFO flash_loader.c: Successfully loaded flash loader in sram
|
||||
11/11 pages written
|
||||
2018-04-10T22:04:35 INFO common.c: Starting verification of write complete
|
||||
2018-04-10T22:04:35 INFO common.c: Flash written and verified! jolly good!
|
||||
|
||||
```
|
||||
|
||||
我没有将 NRST 信号连接到编程器，因此无法使用 _-reset_ 选项，必须按下 reset 按钮才能运行程序。
|
||||
|
||||
|
||||
|
||||
看来，_st-flash_ 与此板配合使用有点不可靠 (通常需要重置 ST-LINK 加密狗)。此外，当前版本不会通过 SWD 发出 reset 命令 (仅使用 NRST 信号)。 软件重置是不现实的，但是它通常是有效的，缺少它会将会带来不便。对于<ruby>电路板-程序员<rt>board-programmer</rt></ruby> 组合 _OpenOCD_ 工作得更好。
|
||||
|
||||
### UART
|
||||
|
||||
UART（<ruby>通用异步收发传输器<rt>Universal Aynchronous Receiver-Transmitter</rt></ruby>）仍然是当今微控制器最重要的外设之一。它的优点是以下属性的独特组合：
|
||||
|
||||
* 相对较高的速度，
|
||||
|
||||
* 仅两条信号线（在 <ruby>半双工<rt>half-duplex</rt></ruby> 通信的情况下甚至一条），
|
||||
|
||||
* 角色对称，
|
||||
|
||||
* 关于新数据的 <ruby>同步带内信令<rt>synchronous in-band signaling</rt></ruby>（起始位），
|
||||
|
||||
* 在传输 <ruby>字<rt>words</rt></ruby> 内的精确计时。
|
||||
|
||||
|
||||
这使得最初用于传输由 7-9 位 words 组成的异步消息的 UART，也被用于有效地实现各种其他物理协议，例如被 [WS28xx LEDs][7] 或 [1-wire][8] 设备使用的协议。
|
||||
|
||||
但是，我们将以其通常的角色使用 UART：从程序中打印文本消息。
|
||||
|
||||
```
|
||||
package main
|
||||
|
||||
import (
|
||||
"io"
|
||||
"rtos"
|
||||
|
||||
"stm32/hal/dma"
|
||||
"stm32/hal/gpio"
|
||||
"stm32/hal/irq"
|
||||
"stm32/hal/system"
|
||||
"stm32/hal/system/timer/systick"
|
||||
"stm32/hal/usart"
|
||||
)
|
||||
|
||||
var tts *usart.Driver
|
||||
|
||||
func init() {
|
||||
system.SetupPLL(8, 1, 48/8)
|
||||
systick.Setup(2e6)
|
||||
|
||||
gpio.A.EnableClock(true)
|
||||
tx := gpio.A.Pin(9)
|
||||
|
||||
tx.Setup(&gpio.Config{Mode: gpio.Alt})
|
||||
tx.SetAltFunc(gpio.USART1_AF1)
|
||||
d := dma.DMA1
|
||||
d.EnableClock(true)
|
||||
tts = usart.NewDriver(usart.USART1, d.Channel(2, 0), nil, nil)
|
||||
tts.Periph().EnableClock(true)
|
||||
tts.Periph().SetBaudRate(115200)
|
||||
tts.Periph().Enable()
|
||||
tts.EnableTx()
|
||||
|
||||
rtos.IRQ(irq.USART1).Enable()
|
||||
rtos.IRQ(irq.DMA1_Channel2_3).Enable()
|
||||
}
|
||||
|
||||
func main() {
|
||||
io.WriteString(tts, "Hello, World!\r\n")
|
||||
}
|
||||
|
||||
func ttsISR() {
|
||||
tts.ISR()
|
||||
}
|
||||
|
||||
func ttsDMAISR() {
|
||||
tts.TxDMAISR()
|
||||
}
|
||||
|
||||
//c:__attribute__((section(".ISRs")))
|
||||
var ISRs = [...]func(){
|
||||
irq.USART1: ttsISR,
|
||||
irq.DMA1_Channel2_3: ttsDMAISR,
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
您会发现此代码可能有些复杂，但目前 STM32 HAL 中没有更简单的 UART 驱动程序（在某些情况下，简单的轮询驱动程序可能会很有用）。 _usart.Driver_ 是使用 DMA 和中断来卸载 CPU 的高效驱动程序。
|
||||
|
||||
STM32 USART 外设提供传统的 UART 及其同步版本。要将其用作输出，我们必须将其 Tx 信号连接到正确的 GPIO 引脚：
|
||||
|
||||
```
|
||||
tx.Setup(&gpio.Config{Mode: gpio.Alt})
|
||||
tx.SetAltFunc(gpio.USART1_AF1)
|
||||
```
|
||||
|
||||
在 Tx-only 模式下配置 _usart.Driver_ （rxdma 和 rxbuf 设置为 nil）：
|
||||
|
||||
```
|
||||
tts = usart.NewDriver(usart.USART1, d.Channel(2, 0), nil, nil)
|
||||
```
|
||||
|
||||
我们使用它的 _WriteString_ 方法来打印这句名句。让我们清理所有内容并编译该程序：
|
||||
|
||||
```
|
||||
$ cd $HOME/emgo
|
||||
$ ./clean.sh
|
||||
$ cd $HOME/firstemgo
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
12728 236 176 13140 3354 cortexm0.elf
|
||||
```
|
||||
|
||||
要查看某些内容，您需要在 PC 中使用 UART 外设。
|
||||
|
||||
**请勿使用 RS232 端口或 USB 转 RS232 转换器！**
|
||||
|
||||
STM32 系列使用 3.3V 逻辑，但是 RS232 可以产生 -15 V ~ +15 V 的电压，这可能会损坏您的 MCU。您需要使用 3.3 V 逻辑的 USB 转 UART 转换器。流行的转换器基于 FT232 或 CP2102 芯片。
|
||||
|
||||
|
||||
|
||||
您还需要一些终端仿真程序 (我更喜欢 [picocom][9])。刷新新图像，运行终端仿真器，然后按几次 reset 按钮：
|
||||
|
||||
```
|
||||
$ openocd -d0 -f interface/stlink.cfg -f target/stm32f0x.cfg -c 'init; program cortexm0.elf; reset run; exit'
|
||||
Open On-Chip Debugger 0.10.0+dev-00319-g8f1f912a (2018-03-07-19:20)
|
||||
Licensed under GNU GPL v2
|
||||
For bug reports, read
|
||||
http://openocd.org/doc/doxygen/bugs.html
|
||||
debug_level: 0
|
||||
adapter speed: 1000 kHz
|
||||
adapter_nsrst_delay: 100
|
||||
none separate
|
||||
adapter speed: 950 kHz
|
||||
target halted due to debug-request, current mode: Thread
|
||||
xPSR: 0xc1000000 pc: 0x080016f4 msp: 0x20000a20
|
||||
adapter speed: 4000 kHz
|
||||
** Programming Started **
|
||||
auto erase enabled
|
||||
target halted due to breakpoint, current mode: Thread
|
||||
xPSR: 0x61000000 pc: 0x2000003a msp: 0x20000a20
|
||||
wrote 13312 bytes from file cortexm0.elf in 1.020185s (12.743 KiB/s)
|
||||
** Programming Finished **
|
||||
adapter speed: 950 kHz
|
||||
$
|
||||
$ picocom -b 115200 /dev/ttyUSB0
|
||||
picocom v3.1
|
||||
|
||||
port is : /dev/ttyUSB0
|
||||
flowcontrol : none
|
||||
baudrate is : 115200
|
||||
parity is : none
|
||||
databits are : 8
|
||||
stopbits are : 1
|
||||
escape is : C-a
|
||||
local echo is : no
|
||||
noinit is : no
|
||||
noreset is : no
|
||||
hangup is : no
|
||||
nolock is : no
|
||||
send_cmd is : sz -vv
|
||||
receive_cmd is : rz -vv -E
|
||||
imap is :
|
||||
omap is :
|
||||
emap is : crcrlf,delbs,
|
||||
logfile is : none
|
||||
initstring : none
|
||||
exit_after is : not set
|
||||
exit is : no
|
||||
|
||||
Type [C-a] [C-h] to see available commands
|
||||
Terminal ready
|
||||
Hello, World!
|
||||
Hello, World!
|
||||
Hello, World!
|
||||
```
|
||||
|
||||
每次按下 reset 按钮都会产生新的 “Hello，World！”行。一切都在按预期进行。
|
||||
|
||||
要查看此 MCU 的 <ruby>双向<rt>bi-directional</rt></ruby> UART 代码，请查看 [此示例][10]。
|
||||
|
||||
### io.Writer 接口
|
||||
|
||||
_io.Writer_ 接口可能是 Go 中第二种最常用的接口类型，紧接在 _error_ 接口之后。其定义如下所示：
|
||||
|
||||
```
|
||||
type Writer interface {
|
||||
Write(p []byte) (n int, err error)
|
||||
}
|
||||
```
|
||||
|
||||
_usart.Driver_ 实现了 _io.Writer_ ，因此我们可以替换：
|
||||
|
||||
```
|
||||
tts.WriteString("Hello, World!\r\n")
|
||||
```
|
||||
|
||||
为
|
||||
|
||||
```
|
||||
io.WriteString(tts, "Hello, World!\r\n")
|
||||
```
|
||||
|
||||
此外，您需要将 _io_ 包添加到 _import_ 部分。
|
||||
|
||||
_io.WriteString_ 函数的声明如下所示：
|
||||
|
||||
```
|
||||
func WriteString(w Writer, s string) (n int, err error)
|
||||
```
|
||||
|
||||
如您所见，_io.WriteString_ 允许使用实现了 _io.Writer_ 接口的任何类型来编写字符串。在内部，它检查基础类型是否具有 _WriteString_ 方法，并使用该方法代替 _Write_ (如果可用)。
|
||||
|
||||
让我们编译修改后的程序：
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
15456 320 248 16024 3e98 cortexm0.elf
|
||||
```
|
||||
|
||||
如您所见，_io.WriteString_ 导致二进制文件的大小显着增加：15776-12964 = 2812字节。 Flash 上没有太多空间了。是什么引起了这么大规模的增长？
|
||||
|
||||
使用这个命令：
|
||||
|
||||
```
|
||||
arm-none-eabi-nm --print-size --size-sort --radix=d cortexm0.elf
|
||||
```
|
||||
|
||||
我们可以打印两种情况下按其大小排序的所有符号。通过过滤和分析获得的数据（awk，diff），我们可以找到大约 80 个新符号。最大的十个如下所示：
|
||||
|
||||
```
|
||||
> 00000062 T stm32$hal$usart$Driver$DisableRx
|
||||
> 00000072 T stm32$hal$usart$Driver$RxDMAISR
|
||||
> 00000076 T internal$Type$Implements
|
||||
> 00000080 T stm32$hal$usart$Driver$EnableRx
|
||||
> 00000084 t errors$New
|
||||
> 00000096 R $8$stm32$hal$usart$Driver$$
|
||||
> 00000100 T stm32$hal$usart$Error$Error
|
||||
> 00000360 T io$WriteString
|
||||
> 00000660 T stm32$hal$usart$Driver$Read
|
||||
```
|
||||
|
||||
因此，即使我们不使用 _usart.Driver.Read_ 方法进行编译，也与 _DisableRx_、_RxDMAISR_、_EnableRx_ 以及上面未提及的其他方法相同。不幸的是，如果您为接口赋值了一些内容，那么它的完整方法集是必需的（包含所有依赖项）。对于使用大多数方法的大型程序来说，这不是问题。但是对于我们这种极简的情况而言，这是一个巨大的负担。
|
||||
|
||||
我们已经接近 MCU 的极限，但让我们尝试打印一些数字（您需要在 _import_ 部分中用 _strconv_ 替换 _io_ 包）：
|
||||
|
||||
```
|
||||
func main() {
|
||||
a := 12
|
||||
b := -123
|
||||
|
||||
tts.WriteString("a = ")
|
||||
strconv.WriteInt(tts, a, 10, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
tts.WriteString("b = ")
|
||||
strconv.WriteInt(tts, b, 10, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
|
||||
tts.WriteString("hex(a) = ")
|
||||
strconv.WriteInt(tts, a, 16, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
tts.WriteString("hex(b) = ")
|
||||
strconv.WriteInt(tts, b, 16, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
}
|
||||
```
|
||||
|
||||
与使用 _io.WriteString_ 函数的情况一样，_strconv.WriteInt_ 的第一个参数的类型为 _io.Writer_ 。
|
||||
|
||||
|
||||
```
|
||||
$ egc
|
||||
/usr/local/arm/bin/arm-none-eabi-ld: /home/michal/firstemgo/cortexm0.elf section `.rodata' will not fit in region `Flash'
|
||||
/usr/local/arm/bin/arm-none-eabi-ld: region `Flash' overflowed by 692 bytes
|
||||
exit status 1
|
||||
```
|
||||
|
||||
这一次我们的空间用完了。让我们试着精简一下有关类型的信息：
|
||||
|
||||
```
|
||||
$ cd $HOME/emgo
|
||||
$ ./clean.sh
|
||||
$ cd $HOME/firstemgo
|
||||
$ egc -nf -nt
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
15876 316 320 16512 4080 cortexm0.elf
|
||||
```
|
||||
|
||||
很接近，但很合适。让我们加载并运行此代码：
|
||||
|
||||
```
|
||||
a = 12
|
||||
b = -123
|
||||
hex(a) = c
|
||||
hex(b) = -7b
|
||||
```
|
||||
|
||||
Emgo 中的 _strconv_ 包与 Go 中的原型有很大的不同。 它旨在直接用于写入格式化的数字，并且在许多情况下可以替换繁重的 _fmt_ 包。 这就是为什么函数名称以 _Write_ 而不是 _Format_ 开头，并具有额外的两个参数的原因。 以下是其用法示例：
|
||||
|
||||
```
|
||||
func main() {
|
||||
b := -123
|
||||
strconv.WriteInt(tts, b, 10, 0, 0)
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, 6, ' ')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, 6, '0')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, 6, '.')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, -6, ' ')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, -6, '0')
|
||||
tts.WriteString("\r\n")
|
||||
strconv.WriteInt(tts, b, 10, -6, '.')
|
||||
tts.WriteString("\r\n")
|
||||
}
|
||||
```
|
||||
|
||||
下面是它的输出：
|
||||
|
||||
```
|
||||
-123
|
||||
-123
|
||||
-00123
|
||||
..-123
|
||||
-123
|
||||
-123
|
||||
-123..
|
||||
```
|
||||
|
||||
### Unix 流 和 <ruby>莫尔斯电码<rt>Morse code</rt></ruby>
|
||||
|
||||
得益于事实上大多数写入功能的函数都使用 _io.Writer_ 而不是具体类型（例如 C 中的 _FILE_ ），因此我们获得了类似于 _Unix stream_ 的功能。在 Unix 中，我们可以轻松地组合简单的命令来执行更大的任务。例如，我们可以通过以下方式将文本写入文件：
|
||||
|
||||
```
|
||||
echo "Hello, World!" > file.txt
|
||||
```
|
||||
|
||||
`>` 操作符将前面命令的输出流写入文件。还有 `|` 操作符，用于连接相邻命令的输出流和输入流。
|
||||
|
||||
|
||||
多亏了流，我们可以轻松地转换/过滤任何命令的输出。例如，要将所有字母转换为大写，我们可以通过 _tr_ 命令过滤 echo 的输出：
|
||||
```
|
||||
echo "Hello, World!" | tr a-z A-Z > file.txt
|
||||
```
|
||||
|
||||
为了显示 _io.Writer_ 和 Unix 流之间的类比，让我们编写以下代码：
|
||||
|
||||
```
|
||||
io.WriteString(tts, "Hello, World!\r\n")
|
||||
```
|
||||
|
||||
采用以下伪 unix 形式：
|
||||
|
||||
```
|
||||
io.WriteString "Hello, World!" | usart.Driver usart.USART1
|
||||
```
|
||||
|
||||
下一个示例将显示如何执行此操作：
|
||||
|
||||
```
|
||||
io.WriteString "Hello, World!" | MorseWriter | usart.Driver usart.USART1
|
||||
```
|
||||
|
||||
让我们来创建一个简单的编码器，它使用莫尔斯电码对写入的文本进行编码：
|
||||
|
||||
```
|
||||
type MorseWriter struct {
|
||||
W io.Writer
|
||||
}
|
||||
|
||||
func (w *MorseWriter) Write(s []byte) (int, error) {
|
||||
var buf [8]byte
|
||||
for n, c := range s {
|
||||
switch {
|
||||
case c == '\n':
|
||||
c = ' ' // Replace new lines with spaces.
|
||||
case 'a' <= c && c <= 'z':
|
||||
c -= 'a' - 'A' // Convert to upper case.
|
||||
}
|
||||
if c < ' ' || 'Z' < c {
|
||||
continue // c is outside ASCII [' ', 'Z']
|
||||
}
|
||||
var symbol morseSymbol
|
||||
if c == ' ' {
|
||||
symbol.length = 1
|
||||
buf[0] = ' '
|
||||
} else {
|
||||
symbol = morseSymbols[c-'!']
|
||||
for i := uint(0); i < uint(symbol.length); i++ {
|
||||
if (symbol.code>>i)&1 != 0 {
|
||||
buf[i] = '-'
|
||||
} else {
|
||||
buf[i] = '.'
|
||||
}
|
||||
}
|
||||
}
|
||||
buf[symbol.length] = ' '
|
||||
if _, err := w.W.Write(buf[:symbol.length+1]); err != nil {
|
||||
return n, err
|
||||
}
|
||||
}
|
||||
return len(s), nil
|
||||
}
|
||||
|
||||
type morseSymbol struct {
|
||||
code, length byte
|
||||
}
|
||||
|
||||
//emgo:const
|
||||
var morseSymbols = [...]morseSymbol{
|
||||
{1<<0 | 1<<1 | 1<<2, 4}, // ! ---.
|
||||
{1<<1 | 1<<4, 6}, // " .-..-.
|
||||
{}, // #
|
||||
{1<<3 | 1<<6, 7}, // $ ...-..-
|
||||
|
||||
// Some code omitted...
|
||||
|
||||
{1<<0 | 1<<3, 4}, // X -..-
|
||||
{1<<0 | 1<<2 | 1<<3, 4}, // Y -.--
|
||||
{1<<0 | 1<<1, 4}, // Z --..
|
||||
}
|
||||
```
|
||||
|
||||
您可以在 [这里][11] 找到完整的 _morseSymbols_ 数组。 `//emgo:const` 指令确保 _morseSymbols_ 数组不会被复制到 RAM 中。
|
||||
|
||||
现在我们可以通过两种方式打印句子：
|
||||
|
||||
```
|
||||
func main() {
|
||||
s := "Hello, World!\r\n"
|
||||
mw := &MorseWriter{tts}
|
||||
|
||||
io.WriteString(tts, s)
|
||||
io.WriteString(mw, s)
|
||||
}
|
||||
```
|
||||
|
||||
我们使用指向 _MorseWriter_ `&MorseWriter{tts}` 的指针而不是简单的 `MorseWriter{tts}` 值，因为 _MorseWriter_ 太大，不适合接口变量。
|
||||
|
||||
|
||||
与 Go 不同，Emgo 不会为存储在接口变量中的值动态分配内存。接口类型的大小受限制，等于三个指针（适合 _slice_ ）或两个 _float64_（适合 _complex128_ ）的大小，以较大者为准。它可以直接存储所有基本类型和小型 “结构体/数组” 的值，但是对于较大的值，您必须使用指针。
|
||||
|
||||
让我们编译此代码并查看其输出：
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
15152 324 248 15724 3d6c cortexm0.elf
|
||||
```
|
||||
|
||||
```
|
||||
Hello, World!
|
||||
.... . .-.. .-.. --- --..-- .-- --- .-. .-.. -.. ---.
|
||||
```
|
||||
|
||||
### 终极 Blinky
|
||||
|
||||
_Blinky_ 等效于 _Hello，World！_ 程序的硬件。一旦有了 Morse 编码器，我们就可以轻松地将两者结合起来以获得 _Ultimate Blinky_ 程序：
|
||||
|
||||
```
|
||||
package main
|
||||
|
||||
import (
|
||||
"delay"
|
||||
"io"
|
||||
|
||||
"stm32/hal/gpio"
|
||||
"stm32/hal/system"
|
||||
"stm32/hal/system/timer/systick"
|
||||
)
|
||||
|
||||
var led gpio.Pin
|
||||
|
||||
func init() {
|
||||
system.SetupPLL(8, 1, 48/8)
|
||||
systick.Setup(2e6)
|
||||
|
||||
gpio.A.EnableClock(false)
|
||||
led = gpio.A.Pin(4)
|
||||
|
||||
cfg := gpio.Config{Mode: gpio.Out, Driver: gpio.OpenDrain, Speed: gpio.Low}
|
||||
led.Setup(&cfg)
|
||||
}
|
||||
|
||||
type Telegraph struct {
|
||||
Pin gpio.Pin
|
||||
Dotms int // Dot length [ms]
|
||||
}
|
||||
|
||||
func (t Telegraph) Write(s []byte) (int, error) {
|
||||
for _, c := range s {
|
||||
switch c {
|
||||
case '.':
|
||||
t.Pin.Clear()
|
||||
delay.Millisec(t.Dotms)
|
||||
t.Pin.Set()
|
||||
delay.Millisec(t.Dotms)
|
||||
case '-':
|
||||
t.Pin.Clear()
|
||||
delay.Millisec(3 * t.Dotms)
|
||||
t.Pin.Set()
|
||||
delay.Millisec(t.Dotms)
|
||||
case ' ':
|
||||
delay.Millisec(3 * t.Dotms)
|
||||
}
|
||||
}
|
||||
return len(s), nil
|
||||
}
|
||||
|
||||
func main() {
|
||||
telegraph := &MorseWriter{Telegraph{led, 100}}
|
||||
for {
|
||||
io.WriteString(telegraph, "Hello, World! ")
|
||||
}
|
||||
}
|
||||
|
||||
// Some code omitted...
|
||||
|
||||
```
|
||||
|
||||
在上面的示例中，我省略了 _MorseWriter_ 类型的定义，因为它已在前面展示过。完整版可通过 [这里][12] 获取。让我们编译它并运行：
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
11772 244 244 12260 2fe4 cortexm0.elf
|
||||
```
|
||||
|
||||
|
||||
|
||||
### 反射
|
||||
|
||||
是的，Emgo 支持 [反射][13]。 _reflect_ 包尚未完成，但是已完成的部分足以实现 _fmt.Print_ 函数族了。来看看我们可以在小型 MCU 上做什么。
|
||||
|
||||
为了减少内存使用，我们将使用 [semihosting][14] 作为标准输出。为了方便起见，我们还编写了简单的 _println_ 函数，它在某种程度上类似于 _fmt.Println_。
|
||||
|
||||
```
|
||||
package main
|
||||
|
||||
import (
|
||||
"debug/semihosting"
|
||||
"reflect"
|
||||
"strconv"
|
||||
|
||||
"stm32/hal/system"
|
||||
"stm32/hal/system/timer/systick"
|
||||
)
|
||||
|
||||
var stdout semihosting.File
|
||||
|
||||
func init() {
|
||||
system.SetupPLL(8, 1, 48/8)
|
||||
systick.Setup(2e6)
|
||||
|
||||
var err error
|
||||
stdout, err = semihosting.OpenFile(":tt", semihosting.W)
|
||||
for err != nil {
|
||||
}
|
||||
}
|
||||
|
||||
type stringer interface {
|
||||
String() string
|
||||
}
|
||||
|
||||
func println(args ...interface{}) {
|
||||
for i, a := range args {
|
||||
if i > 0 {
|
||||
stdout.WriteString(" ")
|
||||
}
|
||||
switch v := a.(type) {
|
||||
case string:
|
||||
stdout.WriteString(v)
|
||||
case int:
|
||||
strconv.WriteInt(stdout, v, 10, 0, 0)
|
||||
case bool:
|
||||
strconv.WriteBool(stdout, v, 't', 0, 0)
|
||||
case stringer:
|
||||
stdout.WriteString(v.String())
|
||||
default:
|
||||
stdout.WriteString("%unknown")
|
||||
}
|
||||
}
|
||||
stdout.WriteString("\r\n")
|
||||
}
|
||||
|
||||
type S struct {
|
||||
A int
|
||||
B bool
|
||||
}
|
||||
|
||||
func main() {
|
||||
p := &S{-123, true}
|
||||
|
||||
v := reflect.ValueOf(p)
|
||||
|
||||
println("kind(p) =", v.Kind())
|
||||
println("kind(*p) =", v.Elem().Kind())
|
||||
println("type(*p) =", v.Elem().Type())
|
||||
|
||||
v = v.Elem()
|
||||
|
||||
println("*p = {")
|
||||
for i := 0; i < v.NumField(); i++ {
|
||||
ft := v.Type().Field(i)
|
||||
fv := v.Field(i)
|
||||
println(" ", ft.Name(), ":", fv.Interface())
|
||||
}
|
||||
println("}")
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
_semihosting.OpenFile_ 函数允许在主机端 打开/创建 文件。特殊路径 _:tt_ 对应于主机的标准输出。
|
||||
|
||||
_println_ 函数接受任意数量的参数，每个参数的类型都是任意的：
|
||||
|
||||
```
|
||||
func println(args ...interface{})
|
||||
```
|
||||
|
||||
可能是因为任何类型都实现了空接口 _interface{}_。 _println_ 使用 [类型开关][15] 打印字符串，整数和布尔值：
|
||||
|
||||
```
|
||||
switch v := a.(type) {
|
||||
case string:
|
||||
stdout.WriteString(v)
|
||||
case int:
|
||||
strconv.WriteInt(stdout, v, 10, 0, 0)
|
||||
case bool:
|
||||
strconv.WriteBool(stdout, v, 't', 0, 0)
|
||||
case stringer:
|
||||
stdout.WriteString(v.String())
|
||||
default:
|
||||
stdout.WriteString("%unknown")
|
||||
}
|
||||
```
|
||||
|
||||
此外，它还支持任何实现了 _stringer_ 接口的类型，即任何具有 _String()_ 方法的类型。在任何 _case_ 子句中，_v_ 变量具有正确的类型，与 _case_ 关键字后列出的类型相同。
|
||||
|
||||
|
||||
reflect.ValueOf(p) 函数以允许以编程方式分析其类型和内容的形式返回 _p_。如您所见，我们甚至可以使用 `v.Elem()` 取消引用指针，并打印所有结构体及其名称。
|
||||
|
||||
让我们尝试编译这段代码。现在，让我们看看如果不使用类型和字段名进行编译会产生什么结果：
|
||||
|
||||
```
|
||||
$ egc -nt -nf
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
16028 216 312 16556 40ac cortexm0.elf
|
||||
```
|
||||
|
||||
闪存上只剩下 140 个可用字节。让我们使用启用了 semihosting 的 OpenOCD 加载它：
|
||||
|
||||
```
|
||||
$ openocd -d0 -f interface/stlink.cfg -f target/stm32f0x.cfg -c 'init; program cortexm0.elf; arm semihosting enable; reset run'
|
||||
Open On-Chip Debugger 0.10.0+dev-00319-g8f1f912a (2018-03-07-19:20)
|
||||
Licensed under GNU GPL v2
|
||||
For bug reports, read
|
||||
http://openocd.org/doc/doxygen/bugs.html
|
||||
debug_level: 0
|
||||
adapter speed: 1000 kHz
|
||||
adapter_nsrst_delay: 100
|
||||
none separate
|
||||
adapter speed: 950 kHz
|
||||
target halted due to debug-request, current mode: Thread
|
||||
xPSR: 0xc1000000 pc: 0x08002338 msp: 0x20000a20
|
||||
adapter speed: 4000 kHz
|
||||
** Programming Started **
|
||||
auto erase enabled
|
||||
target halted due to breakpoint, current mode: Thread
|
||||
xPSR: 0x61000000 pc: 0x2000003a msp: 0x20000a20
|
||||
wrote 16384 bytes from file cortexm0.elf in 0.700133s (22.853 KiB/s)
|
||||
** Programming Finished **
|
||||
semihosting is enabled
|
||||
adapter speed: 950 kHz
|
||||
kind(p) = ptr
|
||||
kind(*p) = struct
|
||||
type(*p) =
|
||||
*p = {
|
||||
X. : -123
|
||||
X. : true
|
||||
}
|
||||
```
|
||||
|
||||
如果您实际运行过此代码，则会注意到 semihosting 运行缓慢，尤其是在逐字节写入时（缓冲很有用）。
|
||||
|
||||
如您所见，`*p` 没有类型名称，并且所有结构字段都具有相同的 _X._ 名称。让我们再次编译该程序，这次不带 _-nt -nf_ 选项：
|
||||
|
||||
```
|
||||
$ egc
|
||||
$ arm-none-eabi-size cortexm0.elf
|
||||
text data bss dec hex filename
|
||||
16052 216 312 16580 40c4 cortexm0.elf
|
||||
```
|
||||
|
||||
现在已经包括了类型和字段名称，但仅在 ~~_main.go_ 文件中~~ _main_ 包中定义了它们。该程序的输出如下所示：
|
||||
|
||||
```
|
||||
kind(p) = ptr
|
||||
kind(*p) = struct
|
||||
type(*p) = S
|
||||
*p = {
|
||||
A : -123
|
||||
B : true
|
||||
}
|
||||
```
|
||||
|
||||
反射是任何易于使用的序列化库的关键部分，而像 [JSON][16] 这样的序列化 ~~算法~~ 在<ruby>物联网<rt>IoT</rt></ruby>时代也越来越重要。
|
||||
|
||||
这些就是我完成的本文的第二部分。我认为有机会进行第三部分，更具娱乐性的部分，在那里我们将各种有趣的设备连接到这块板上。如果这块板装不下，我们就换一块大一点的。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://ziutek.github.io/2018/04/14/go_on_very_small_hardware2.html
|
||||
|
||||
作者：[Michał Derkacz ][a]
|
||||
译者：[gxlct008](https://github.com/gxlct008)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]:https://ziutek.github.io/
|
||||
[1]:https://ziutek.github.io/2018/04/14/go_on_very_small_hardware2.html
|
||||
[2]:https://ziutek.github.io/2018/03/30/go_on_very_small_hardware.html
|
||||
[3]:https://golang.org/doc/effective_go.html#interfaces
|
||||
[4]:https://research.swtch.com/interfaces
|
||||
[5]:https://blog.golang.org/laws-of-reflection
|
||||
[6]:https://github.com/texane/stlink
|
||||
[7]:http://www.world-semi.com/solution/list-4-1.html
|
||||
[8]:https://en.wikipedia.org/wiki/1-Wire
|
||||
[9]:https://github.com/npat-efault/picocom
|
||||
[10]:https://github.com/ziutek/emgo/blob/master/egpath/src/stm32/examples/f030-demo-board/usart/main.go
|
||||
[11]:https://github.com/ziutek/emgo/blob/master/egpath/src/stm32/examples/f030-demo-board/morseuart/main.go
|
||||
[12]:https://github.com/ziutek/emgo/blob/master/egpath/src/stm32/examples/f030-demo-board/morseled/main.go
|
||||
[13]:https://blog.golang.org/laws-of-reflection
|
||||
[14]:http://infocenter.arm.com/help/topic/com.arm.doc.dui0471g/Bgbjjgij.html
|
||||
[15]:https://golang.org/doc/effective_go.html#type_switch
|
||||
[16]:https://en.wikipedia.org/wiki/JSON
|
||||
Loading…
Reference in New Issue
Block a user