The SigGen.asm in the attached project is basically a stripped down version of the SPORT1_ISR_process_samples_.asm file found in the 21489 AD1939 I2S C Sampled-Based Talkthru example.
I've spent too much time trying to figure it out. I'm sure someone with more experience could find it in a couple of minutes.
Ideally when command==2, SigGen is executed and the resulting the signal is passed through the FIR filter and then out to DAC.
At this point it as long as SigGen creates the signal and passes it to the DAC id be ecstatic.