Run Go applications on Pico using TinyGo

利用 TinyGo 編譯出運行在
microcontroller 的 Golang 程式
Cherie Hsieh @ PUFsecurity from eMemory

WhoAmI
Cherie Hsieh
Senior Frimware & Software Engineer @ PUFsecurity
1. Golang Community Co-organizer
2. GDG Hsinchu Organizer
3. Google WTM
4. Master student at NYCU
矽智財（IP）廠商力旺（3529）昨（21）日
股價強攻漲停，收盤以 2,340元平歷史
高價的姿態，擠下伺服器管理晶片
（BMC）廠信驊，成為台股第二高價股，
僅次於股王矽力。

Golang for Embedded
Reﬂections on 10 years of Go (devfast 2019)
If MicroPython is gaining traction as a language for embedded, I think Go is a
far better candidate.

Golang for Embedded
TinyGo - A Go Compiler For Small Places
(Target devices for 8K to 32K of RAM)

Golang for Embedded
package main
import (
"machine"
"time"
)
func main() {
led := machine.LED
led.Conﬁgure(machine.PinConﬁg{Mode: machine.PinOutput})
for {
led.Low()
time.Sleep(time.Millisecond * 500)
led.High()
time.Sleep(time.Millisecond * 500)
}
}
Demo

How TinyGo works
tinygo build -o blink -target="pico" ./blink.go
TinyGo options
Go standard
compiler lib
TinyGo
interpreter
SSA
LLVM
IR
Go does a lot of initialization at runtime, which is really bad for code size.
So TinyGo interprets these functions at compile time as far as it is able to.
static single assignment

How TinyGo works
TinyGo options
Go standard
compiler lib
TinyGo
interpreter
SSA
LLVM
IR
TinyGo
optimizer
LLVM standard
optimizer
object file
string-to-[]byte optimizations

How TinyGo works
object file
object file
object file
LLVM Linker
linker script
binary file

Run TinyGo programs on Pico
1. Bring-up Pico
2. CPU initialization
3. Load user programs
4. Jump to entry point
5. Use a correct register table
6. Target-speciﬁc runtime

Boot Flow of Pico
hardware
controlled boot
CPU
initialization
Load
bootloader
Bootroom
Setup
Flash
Jump to the
entry point
Run the
program
Bootloader

Memory Map

TinyGo configuration for Pico
{ // tinygo/targets/pico.json
"inherits": [
"rp2040"
],
"build-tags": ["pico"],
"serial": "uart", // build be usb or uart
"linkerscript": "targets/pico.ld",
"extra-files": [
"targets/pico-boot-stage2.S" // bootloader
]
}
{ // tinygo/targets/rp2040.json
"inherits": ["cortex-m0plus"],
"build-tags": ["rp2040", "rp"],
"flash-method": "msd",
"msd-volume-name": "RPI-RP2",
"msd-firmware-name": "firmware.uf2",
"binary-format": "uf2",
"uf2-family-id": "0xe48bff56",
"rp2040-boot-patch": true,
"extra-files": [
"src/device/rp/rp2040.s"
],
"openocd-transport": "swd",
"openocd-target": "rp2040"
}

// pico.ld
MEMORY
{
/* Reserve exactly 256 bytes at start of ﬂash for second stage bootloader */
BOOT2_TEXT (rx) : ORIGIN = 0x10000000, LENGTH = 256
FLASH_TEXT (rx) : ORIGIN = 0x10000000 + 256, LENGTH = 2048K - 256
RAM (rwx) : ORIGIN = 0x20000000, LENGTH = 256k
}
INCLUDE "targets/rp2040.ld"

_stack_size = 2K;
SECTIONS
{
/* Second stage bootloader is prepended to the image. It must be 256 bytes
and checksummed. The gap to the checksum is zero-padded.
*/
.boot2 : {
__boot2_start__ = .;
KEEP (*(.boot2));
/* Explicitly allocate space for CRC32 checksum at end of second stage bootloader */
. = __boot2_start__ + 256 - 4;
LONG(0)
} > BOOT2_TEXT = 0x0
}
INCLUDE "targets/arm.ld"

arm
rp2040
processor
microcontroller
Pico
Adafruit Feather
RP2040
board
Inherited configuration

Target-Speciﬁc Runtime
"build-tags": ["pico", "rp2040", "rp"],
// +build rp2040
package runtime
import (
"device/arm"
"machine"
)
// more code
func main() {
preinit()
run() // call main function
abort()
}

Go struct for abstract hardware
src/device/rp
src/machine/machine_rp2040_uart.go
raw register table
abstract hardware struct

Go struct for abstract hardware
type UART struct {
Buffer *RingBuffer
Bus *rp.UART0_Type
Interrupt interrupt.Interrupt
}
// Configure the UART.
func (uart *UART) Configure(config UARTConfig) error {
// more code ...
}

The diﬀerences between
Go programs and TinyGo programs
1. Goroutine & Scheduler
Go - User Space Scheduling TinyGo - FIFO Scheduling
https://golangbyexample.com/goroutines-golang/
run queue
sleep queue
G1 G2
G3

The diﬀerences between
Go programs and TinyGo programs
1. Memory Management
Go TinyGo
https://about.sourcegraph.com/go/gophercon-2018-allocator-wrestling/

Experiment
Touch Sensor
Pico
Pi 3B
SWD
UART

Experiment
type TouchChange uint8
type Touch struct { // Hardware abstraction struct
pin machine.Pin
intr interrupt.Interrupt
action func()
change TouchChange
}
func NewTouch(pin machine.Pin, change TouchChange, action func()) *Touch {
touch := &interTouch
touch.pin = pin
touch.action = action
touch.change = change
touch.intr = interrupt.New(rp.IRQ_IO_IRQ_BANK0, interTouch.handleInterrupt)
return touch
}

Experiment
func main() {
led.Conﬁgure(machine.PinConﬁg{Mode: machine.PinOutput})
touchAtion := func(){
if led.Get() {
led.Low()
} else {
led.High()
}
}
touch := NewTouch(machine.GPIO28, Touched, touchAtion)
touch.Enable();
select{}
}

Debug
openOCD
(debug Translator)
GDB server
GDB client
Debug Access
Port
Debugger
Interface
Break/Watch
Point Unit
Cortex M0+
Core
SWD
Pi 3B (host) Pico

Challenges
1. Reused v.s full-customized board conﬁgurations.
2. Insufﬁcient APIs for hardware control.
3. Parts of Go features are still a work in progress.

Why this TinyGo exists
We never expected Go to be an embedded language and so its got serious
problems...
Rob Pike, GopherCon 2014 Opening Keynote
The original reasoning was: if Python can run on microcontrollers, then
certainly Go should be able to run on even lower level micros.

Resources
1. https://tinygo.org/
2. https://www.infoq.com/presentations/tiny-go/
3. https://www.raspberrypi.com/documentation/microcontrollers/raspberry-pi-pico.html

Thank You for Your Time.
Cherie Hsieh @ PUFsecurity from eMemory

Run Go applications on Pico using TinyGo

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