The title is misleading so let me explain I have a task that reads data from an SD card and feeds a I2S DAC. original code looked like this and it worked …. but Audio task { while(1) { xTaskNotifyWait(….) … wait for I2S Interrupt to release

    read data from SD card and ready buffers for next I2S package

}

} I2S Interrupt uses xTaskNotifyFromISR() to release loop in Audio task … this occurs every 25 msec The above code works very well with SD card read routines polling for status status. I have found that the first SD card read following a period of no SD card activity (that period is 10 msec) that the SD card can take 3 msec or longer to prodive the sector. 3 msec of spinning doing polling is an unacceptable amount of wasted time. So I changed the SD card routines to wait (also using a xTaskNotifyWait() ) until the SDHC interrupt first indicating the sector was acquired. My problem …. the SD card reads can delay the SD data acquisition process beyond the 25 msec I2S period so when I enter the xTaskNotifyWait() for the SD card – it returns immediatly because the I2S interrupt had issued its xTaskNotifyFromISR(). Is there a way to implement two task notification events without having them interact? (SD xTaskNotifyWait() only responds to SD xTaskNotifyFromISR() and main audio loop xTaskNotifyWait() only respond to IS2 xTaskNotifyFromISR()? I hope I explained this so it makes sense. My one thought is to look at the xTaskNotifyWait() in the SD routine and if it shows I2S then set a flag and re-issue the xTaskNotifyWait. Upon leaving the SD routines check for the flag and if set .. bypass the Audio xTaskNotifyWait() ….. is there a better way? Thanks. Joe

You can set individual bits in the event group https://www.freertos.org/RTOSTaskNotificationAsEvent_Group.html so one interrupt sets one bit, the other interrupt sets another bit, and the task that unblocks checks to see which bits are set to know what to do. Note that the bits don’t latch like they do in a real event group (https://www.freertos.org/FreeRTOS-Event-Groups.html) so using a task notification like this is not really event group behaviour as such – but it does let you distinguish between up to 32 different events having occurred.

Thanks Richard. That is exactly how I solved it.