Errors are part of API, and the exported rp2 errors seemed arbitrary.
For example, the very particular ErrRP2040I2CDisable was exported, but
errI2CWriteTimeout (which is defined on all platforms) is not.
While here, remove "RP2040" from an error name and make the messages
consistent and idiomatic.
The `gosched` call introduce arbitrary long delays in general, and in
TinyGo particular because the goroutine scheduler is cooperative and
doesn't preempt busy (e.g. compute-heavy) goroutines.
Before this change, the timeout logic would read, simplified:
deadline := now() + timeout
startTX()
for !txDone() {
if now() > deadline { return timeoutError }
gosched() // (1)
}
startRx() // (2)
for !rxDone() {
// (3)
if now() > deadline { return timeoutError }
gosched()
}
What could happen in a busy system is:
- The gosched marked (1) would push now() to be > than deadline.
- startRx is called (2), but the call to rxDone immediately after would
report it not yet done.
- The check marked (3) would fail, even though only a miniscule amount
of time has passed between startRx and the check.
This change ensures that the timeout clock discounts time spent in
`gosched`. The logic now reads, around every call to `gosched`:
deadline := now() + timeout
startTX()
for !txDone() {
if now() > deadline { return timeoutError }
before := now()
gosched()
deadline += now() - before
}
I tested this change by simulating a busy goroutine:
go func() {
for {
// Busy.
before := time.Now()
for time.Since(before) < 100*time.Millisecond {
}
// Sleep.
time.Sleep(100 * time.Millisecond)
}
}()
and testing that I2C transfers would no longer time out.
Elias Naur
deadprogram