added tud_task_event_ready() #414
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ported for osal none/freertos/mynewt
to check if there is pending events in the tud task without executing it. Useful to check before entering low power mode with WFI/WFE
since it doesn't make any differences.
src/osal/osal_none.h
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| @@ -203,6 +202,15 @@ static inline bool osal_queue_send(osal_queue_t const qhdl, void const * data, b | |||
| return success; | |||
| } | |||
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| static inline bool osal_queue_empty(osal_queue_t qhdl) | |||
| { | |||
| _osal_q_lock(qhdl); | |||
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This approach won't work.
The user needs to call tud_task_event_ready() with interrupts already disabled in order to check whether the queue is empty. If the queue is empty, then it can issue WFI. If not, it will re-enable interrupts and not issue WFI.
I'm uncertain what happens if you issue cpsid i when interrupts are already disabled, but this function will re-enable them when it exits. If a USB event comes in between the time this function exits and when the calling function issues WFI, then that interrupt will be handled and the queue will no longer be empty, but the calling function will still issue WFI.
This function needs to be called with interrupts already disabled, and shouldn't lock/unlock the system on its own.
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@xobs Yeah, you are right, I was thinking to have this function being used in normal/general mode as well. However, there is not much benefit in normal mode, also locking the queue is not crucial as well in that mode.
NVIC enable probably shouldn't have any impact on the global CPSID, but I could be wrong. I will remove the queue lock/unlock anyway since it is better to do.
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thanks @xobs for reviewing, the pr is merged now. |
Describe the PR
added tud_task_event_ready() to check if there is pending events in the tud task without executing
it. Useful to check before entering low power mode with WFI/WFE. This helps to resovle adafruit/circuitpython#2868
This requires an additional
osal_queue_empty()to be implemented.Additional context
TockOS, like a lot of other operating systems divides interrupt processing in two halves. The top-half runs in interrupt context, which is mapped to ARMv7-M's handler mode. The bottom-half processing happens in kernel context, which is mapped to ARMv7-M's privileged thread mode.
The main USB interrupt processing happens in the bottom half, and within the bottom half we add to TinyUSB task queue. Therefore we can call
wfi, only when both TinyUSB task queue is empty and no more bottom half interrupt processing is left to do.Hence the need for
tud_task_is_queue_empty()function.Originally posted by @rajivr in #279 (comment)