esp32c3 Unable to do any timing faster than 1ms

[mredp-evos]

Trying to use any of the kernel timing functions for anything less than 1ms does not work on the ESP32-C3. I would have thought I just need to increase the CONFIG_SYS_CLOCK_TICKS_PER_SEC to 10000 to get 100us ticks. But this doesn't work.

I have tried various combinations of CONFIG_SYS_CLOCK_TICKS_PER_SEC and CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC. But it always ends up wrong/very innacurate.

To be specific, sometimes 100us delay would be closer to 250us. Or sometimes 100us delay would be 10ms. But I could never get 100us to equal 100us.

Is it possible to do any real-time scheduling in the tens or hundreds of microseconds? Perhaps, I am missing something but 1ms (1kHz) seems a bit slow to be the timing limit for a 160MHz processor.

Thanks,

[mredp-evos]

Narrowed the issue down to esp32c3_sys_timer.c

A quick workaround was to set #define MIN_DELAY to 1. Then when you increase the CONFIG_SYS_CLOCK_TICKS_PER_SEC it won't be capped at 1ms.

I guess MIN_DELAY might be left over from the esp32s2 driver where the HW CYCLES are faster perhaps? Whereas in the esp32c3 HW CYCLE is only 1us which makes MIN_DELAY of 1000 equal 1ms.

I also set to CONFIG_TICKLESS_KERNEL=n but I never tested if this had any effect on the issue. I suspect that it did not.

This lead me to the other issue which is that the CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC is fixed at 1MHz when the clock is a 16MHz clock. This is because the esp32c3_sys_timer.c file uses systimer_hal functions which use SYSTIMER_TICKS_PER_US. And because the systimer_alarm function uses systimer_hal_get_time.

Instead, replace all the systimer_hal functions with systimer_ll functions and systimer_hal_get_time with systimer_hal_get_counter_value instead. Then the CYCLES will be based off 16MHz (62.5ns) instead of 1MHz (1us).

Fixing either the MIN_DELAY issue or the CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC issue will allow you to get faster timings.

[sylvioalves]

Trying to use any of the kernel timing functions for anything less than 1ms does not work on the ESP32-C3. I would have thought I just need to increase the CONFIG_SYS_CLOCK_TICKS_PER_SEC to 10000 to get 100us ticks. But this doesn't work.

I have tried various combinations of CONFIG_SYS_CLOCK_TICKS_PER_SEC and CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC. But it always ends up wrong/very innacurate.

To be specific, sometimes 100us delay would be closer to 250us. Or sometimes 100us delay would be 10ms. But I could never get 100us to equal 100us.

Is it possible to do any real-time scheduling in the tens or hundreds of microseconds? Perhaps, I am missing something but 1ms (1kHz) seems a bit slow to be the timing limit for a 160MHz processor.

Thanks,

Hi, can you describe which kernel timing functions you have been using? And how are you measuring the clock in this scenario?