sleep itself seems to take 9 ms Toit #help

sleep itself seems to take 9 ms

RobvanLopik

04/03/2023, 2:08 PM

try this

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main:
  t0 := Time.monotonic_us  
  1000.repeat:
    sleep --ms=1
  print (Time.monotonic_us - t0)

results in ~9800 instead of 1000. Increasing the sleep time makes the discrepancy go away.

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sleep --ms=0

does not take extra time. I found this because the stepper motor seemed much to slow

floitsch

04/03/2023, 2:47 PM

There is a certain overhead for setting the sleep up. Is that what you are experiencing or is there something else happening for small numbers like 1?

RobvanLopik

04/03/2023, 3:07 PM

I think 9 ms is a lot of overhead. In the stepper 1 ms is used, that effectively is 10 ms making it 10 times slower than expected

floitsch

04/03/2023, 3:08 PM

I agree. Just making sure that's the actual issue.

RobvanLopik

04/03/2023, 3:13 PM

When I run on host there is no overhead! 50 microseconds turns into 133 us

floitsch

04/03/2023, 3:14 PM

Might Reuther be the setup cost or using a timer that isn't precise enough. Both are different on the esp32

floitsch

04/03/2023, 3:17 PM

Just fyi: most of us are on vacation for the next week, so there is likely nothing going to happen in that time. 1. Please remind us when we come back (just in case we forget). 2. As a workaround I would:

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end := Time.monotonic_us + 10_000
while end > Time.monotonic_us: yield

RobvanLopik

04/03/2023, 4:14 PM

Actually, when the host is Windows, the overhead is 15 ms instead of near 0 on Linux

kasperl

04/03/2023, 5:36 PM

It's a timer resolution issue, not really overhead per se.

kasperl

04/03/2023, 5:37 PM

On FreeRTOS, the smallest amount of time we can wait is a tick, which defaults to 10ms. Haven't looked at Windows lately.

kasperl

04/03/2023, 5:38 PM

We eventually hit a pthread_cond_wait: https://github.com/toitlang/toit/blob/995ecf05f0659ac0d3347bd84d181e54a4def311/src/os_win.cc#L99.

kasperl

04/03/2023, 5:40 PM

It's called from here: https://github.com/toitlang/toit/blob/995ecf05f0659ac0d3347bd84d181e54a4def311/src/event_sources/timer.cc#L121.

kasperl

04/03/2023, 5:56 PM

If we can find a better primitive to support precise, cancelable sleep I'd be very supportive of using that instead of pthread_cond_wait with a timeout.

RobvanLopik

04/03/2023, 6:04 PM

Thanks for the info. Maybe worth documenting, because the form sleep --ms= suggests milliseconds are meaningful. Anyway, this makes the steppermotor 10 times slower than expected

kasperl

04/03/2023, 6:05 PM

Yeah, that's a valid point. Maybe we can find a better way to support that than repeated sleeps. Thanks for bringing this up 🙏

RobvanLopik

04/03/2023, 7:11 PM

For the stepper I think I have seen software that uses RMT. For the sleep you may need to roll your own; after all you have a microsecond clock in Time.monotonic_us

kasperl

04/03/2023, 7:20 PM

You can use RMT on Toit.

kasperl

04/03/2023, 7:22 PM

The one-wire package uses this: https://github.com/toitware/toit-1-wire/blob/main/src/one_wire.toit.

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