tud_audio_write()/tud_audio_read() from ISR when using RTOS

[ra1nb0w]

Related area

tusb_fifo

Hardware specification

STM32H563

Is your feature request related to a problem?

I would like to use tud_audio_write() and tud_audio_read() from ISR when RTOS support is enabled (I am using FreeRTOS).
If you call it from ISR you end up with an issue in the mutex [1] since you need to use specific ISR aware functions.

[1]

tinyusb/src/common/tusb_fifo.c

Line 474 in cfbdc44

_ff_lock(f->mutex_wr);

Describe the solution you'd like

At the moment I am using a custom ARM check, see later, but should be nice to have a generic way to do it like bool in_isr or maybe there is another way to do it correctly. My specific use case is calling it from I2S DMA callback.
Thanks

diff --git a/src/common/tusb_fifo.c b/src/common/tusb_fifo.c
index 8a0fd4417..7e4ed81db 100644
--- a/src/common/tusb_fifo.c
+++ b/src/common/tusb_fifo.c
@@ -471,7 +471,7 @@ static uint16_t _tu_fifo_write_n(tu_fifo_t* f, const void * data, uint16_t n, tu
 {
   if ( n == 0 ) return 0;
 
-  _ff_lock(f->mutex_wr);
+  if ( (SCB->ICSR & SCB_ICSR_VECTACTIVE_Msk) == 0 ) _ff_lock(f->mutex_wr);
 
   uint16_t wr_idx = f->wr_idx;
   uint16_t rd_idx = f->rd_idx;
@@ -549,14 +549,14 @@ static uint16_t _tu_fifo_write_n(tu_fifo_t* f, const void * data, uint16_t n, tu
     TU_LOG(TU_FIFO_DBG, "\tnew_wr = %u\r\n", f->wr_idx);
   }
 
-  _ff_unlock(f->mutex_wr);
+  if ( (SCB->ICSR & SCB_ICSR_VECTACTIVE_Msk) == 0 ) _ff_unlock(f->mutex_wr);
 
   return n;
 }
 
 static uint16_t _tu_fifo_read_n(tu_fifo_t* f, void * buffer, uint16_t n, tu_fifo_copy_mode_t copy_mode)
 {
-  _ff_lock(f->mutex_rd);
+  if ( (SCB->ICSR & SCB_ICSR_VECTACTIVE_Msk) == 0 ) _ff_lock(f->mutex_rd);
 
   // Peek the data
   // f->rd_idx might get modified in case of an overflow so we can not use a local variable
@@ -565,7 +565,7 @@ static uint16_t _tu_fifo_read_n(tu_fifo_t* f, void * buffer, uint16_t n, tu_fifo
   // Advance read pointer
   f->rd_idx = advance_index(f->depth, f->rd_idx, n);
 
-  _ff_unlock(f->mutex_rd);
+  if ( (SCB->ICSR & SCB_ICSR_VECTACTIVE_Msk) == 0 ) _ff_unlock(f->mutex_rd);
   return n;
 }
 

I have checked existing issues, dicussion and documentation

• I confirm I have checked existing issues, dicussion and documentation.

[ra1nb0w]

Can be useful to others? How to generalize the idea such that it can be committed in master?
Thanks

[cdesjardins]

Just my 2 cents. this is a bug. It is not ok to just ignore a mutex if you are in ISR. the correct solution is to trigger a task to do the I/O. give a semaphore from ISR, or send a message, that unblocks your task which does the I/O.

[ra1nb0w]

yes, it is a dirty hack and the ignored mutexes are managed by ISR priority. I used your suggestion at the beginning but I would like to copy the I2S data upon I receive the DMA ISR.
Anyway, thanks for your comment.