Enhancements to the Audio API

Goals

Simpler to understand

• The interfaces are currently bloated, this makes knowing who the consumers of a particular function or variable are very difficult.
• The names of functions need to clearly identify not only what they do, but also what context they are to be called in

Thread safety

• The Codec and Audio thread should share zero state-modifying code. Any state modifying function that one calls should never be called on the other. -- Known problem areas:
  • pcmbuf_flush_fillpos
  • pcmbuf_play_stop
  • pcmbuf_play_start
  • skip_next_track
• In the off chance that there is some data that must be modified by both threads, it must not be performance sensitive, and may be protected by a mutex
• Existing use of mutexes to protect functions can be eliminated to improve performance once the above is done.

Performance

The following apply only to performance sensitive sections of code.

• Functions should have specific behavior, rather than conditional branches.
• Some sacrifices to readability for performance is acceptable in these areas
• Keep register usage to a minimum (check in the asm how many registers the compiler is using)

Progress

Steps that I've so far taken are in SVN

PCMBuffer

• now behaves more like a typical buffer where consumers are told how much space is left if they reach the end
• now uses linked lists instead of circular buffer for the buffer descriptors
• performance sensitive code optimized by reading compiled code
• trimmed down the API exposed to consumers

PCM

• Reduced usage of pcm_ function calls outside of pcmbuf.c (this probably wants more doing)
• Reduce latency by only holding the currently playing chunk in PCM.c not the next one too

Playback

Not much done yet