Add PCM audio streaming driver

[WojciechGw]

Add PCM audio streaming driver

Adds raw PCM playback via a ring buffer in XRAM, activated through the existing XREG audio channel (device=0, channel=1, address=2).

XRAM layout

8-byte header at the base address followed by the ring buffer:

Offset	Field	Description
+0..+1	write_ptr	byte index maintained by the application
+2	format	bit 0=mono, bit 1=8-bit, bit 2=unsigned
+3	buf_size_log2	ring size (9–13; default 10)
+4..+5	sample_rate	8000/11025/16000/22050/32000/44100 Hz
+6..+7	read_ptr	byte index written by RP2350 each IRQ
+8..	ring buffer	1 << buf_size_log2 bytes

Supported formats

All combinations of:

• sample rate: 8000 / 11025 / 16000 / 22050 / 32000 / 44100 Hz
• bit depth: 16-bit signed or 8-bit unsigned
• channels: stereo or mono

The RP2350 IRQ runs at the configured sample rate and mixes BEL alert sounds on both channels, consistent with PSG and OPL behaviour. Calling any other audio XREG automatically stops PCM via aud_setup().

Activation

xreg(0, 1, 2, pcm_xram_base);  /* start */
xreg(0, 1, 2, 0xFFFF);         /* stop  */

Additional files

solution notepad
PCM.md
cc65 (c89) test player
playpcm.c
test.wav for test player
testwav.zip

[WojciechGw]

ROM
playpcm.zip
source
playpcm.c
Updated version.
You can now run it with:
load playpcm.rp6502 filetoplay.wav

2nd test .wav
testwav2.zip