SWCODEC:
1) Load compressed audio data from file
2) Decode to PCM
3) Apply DSP processing
4) Send PCM data to DAC via DMA (or FIQ)
[Not currently implemented] Between tracks, check for audio format
change (i.e.. samplerate) and configure DAC
HWCODEC (when PCM playback is implemented):
1) Load compressed audio data from file
2) Prepare data for sending to MAS - (bitswap for MPEG, bitswap and
maybe byteswap (depending on WAV/AIFF) WAV/AIFF, maybe decode
simple compressed formats to bitswapped PCM)
3) Send data to MAS via DMA
Between tracks, may need to swap between MPEG and PCM codecs.