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.