Audio interrupts not working

[phil-opp]

I tried to enable audio interrupts, so that we get an interrupt whenever there is new audio data from the microphone. I did everything in the same as it's done in the official STM32Cube_FW_F7_V1.2.0 code:

• Configure GPIO pin H-15 as input pin.
• Enable various interrupts in the sai.aim/bim registers.
• Configure the syscfg.exticr4 register to use port H for exti15 line.
• Configure and unmask exti15 line.
• Add a interrupt handler for the EXTI15_10 interrupt.

But I still don't receive any audio interrupts. The H-15 pin is always 1, even directly after reading out data, when the register bit that the pin mirrors is 0. So there is a bug somewhere.

For now I just read the audio data on idle as a workaround, but it would be nice if we could get the actual audio interrupts working.