On RP2040, we got incorrect sleep time after a select with timeout

[elbert-wong]

In a channel select with timeout, if the select hit the non-timeout branch, we got incorrect sleep time in the following code.

we got correct sleep time if we: comment out the timer go-routine OR comment out the timeout branch in select

Note: to handle the pin edge interrupt, the #2847 code is merged, the issue is reported as #2877

pinOut signal:

[kenbell]

@elbert-wong - I'm not able to repro on the latest dev branch. I'm seeing the timing below without commenting out any code (I'm using a Pico):

This is to code I'm using:

package main

import (
    "machine"
    "runtime"
    "time"
)

const (
    pinIn  = machine.GPIO13
    pinOut = machine.GPIO15
    pinLED = machine.LED
)

var timeout = make(chan bool, 1)
var tstChan = make(chan bool, 1)

func pinConfig() {
    pinIn.Configure(machine.PinConfig{Mode: machine.PinInputPullup})
    pinLED.Configure(machine.PinConfig{Mode: machine.PinOutput})
    pinOut.Configure(machine.PinConfig{Mode: machine.PinOutput})
}

func main() {
    pinConfig()

    go func() {
        time.Sleep(10000 * time.Millisecond)
        timeout <- true
    }()

    pinIn.SetInterrupt(machine.PinFalling, pinFallHandler)

    select {
    case <-tstChan:
    case <-timeout:
    }

    pinIn.SetInterrupt(machine.PinFalling, nil)

    pinOut.High()
    time.Sleep(100 * time.Millisecond)
    pinOut.Low()
    time.Sleep(300 * time.Millisecond)
    pinOut.High()

    for {
        runtime.Gosched()
    }
}

func pinFallHandler(pin machine.Pin) {
    tstChan <- true
}

[elbert-wong]

@kenbell Thank you for your prompt reply! Could you confirm that the light sleep is enabled in your dev code? (which is also included in release 0.24.0) If I disable the light sleep, the following sleep in main loop works well. But in that case, the select code is blocked for a very long time, if a new ext interrupt triggers again during this block time, we will get a panic (writing a full channel in interrupt).

my issue was found on 0.22.0(with light sleep merged) and also 0.24.0

I have build a dev branch (tinygo version 0.25.0-dev linux/amd64 (using go version go1.18.3 and LLVM version 14.0.6) with outside llvm-14 this morning, still no lucky. But I am not sure whether I am using the tinygo in dev correctly. I just run it as below:

/tinygo build -target=pico -o pico.uf2 -size short github.go And also I have copied the folder lib/compiler-rt-builtins from release 0.24.0. If anything wrong in my steps, please let me know. Thanks!

[elbert-wong]

Seems like I fixed this issue by correcting the sleep duration in addSleepTask. But I have no idea why this code works if light-sleep is not enabled. Probably without light-sleep the "select" code block does not run before any sleeping go-routine wakes up. The interrupt event doesn't wake up the main loop, although who is waiting for the channel reading. The scheduler is in busy loop when ext interrupt fires.