components/driver/rmt: portENTER_CRITICAL called from ISR context

[devsaurus]

This is based on reviewing the code, I haven't yet observed any problems running the code. Not sure if this is really an issue, so feel free to close if considered not relevant.

Function rmt_fill_memory() is called dual-use from task and ISR context. It subsequently calls the portENTER_CRITICAL() and portEXIT_CRITICAL() macros.

But http://www.freertos.org/taskENTER_CRITICAL_taskEXIT_CRITICAL.html states that these macros must not be called from ISR context (e.g. taskENTER_CRITICAL() directly maps to portENTER_CRITICAL() in components/freertos/include/freertos/task.h).

[projectgus]

Hi @devsaurus ,

Thanks for the comprehensive description of what you're seeing.

In IDF, we have made some modifications to standard FreeRTOS behaviour. One of these is that it's safe to call portENTER_CRITICAL() from an ISR. It may be necessary to enter a critical sectio in an ISR, in order to prevent concurrent access by the other CPU.

Some notes about the implementation can be found here in the source code:
https://github.com/espressif/esp-idf/blob/master/components/freertos/include/freertos/portmacro.h#L177

Please feel free to reopen if you believe this behaviour change is causing any bugs.