Am 09.09.23 um 11:48 schrieb Mark Cave-Ayland:
The Apple Sound Chip was primarily used by the Macintosh II to generate sound
in hardware which was previously handled by the toolbox ROM with software
interrupts.
Implement both the standard ASC and also the enhanced ASC (EASC) functionality
which is used in the Quadra 800.
Note that whilst real ASC hardware uses AUDIO_FORMAT_S8, this implementation
uses
AUDIO_FORMAT_U8 instead because AUDIO_FORMAT_S8 is rarely used and not supported
by some audio backends like PulseAudio and DirectSound when played directly with
-audiodev out.mixing-engine=off.
Co-developed-by: Laurent Vivier <laurent@vivier.eu>
Co-developed-by: Volker Rümelin <vr_qemu@t-online.de>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
---
MAINTAINERS | 2 +
hw/audio/Kconfig | 3 +
hw/audio/asc.c | 699 +++++++++++++++++++++++++++++++++++++++++
hw/audio/meson.build | 1 +
hw/audio/trace-events | 10 +
hw/m68k/Kconfig | 1 +
include/hw/audio/asc.h | 84 +++++
7 files changed, 800 insertions(+)
create mode 100644 hw/audio/asc.c
create mode 100644 include/hw/audio/asc.h
Hi Mark,
the function generate_fifo() has four issues. Only the first one
is noticeable.
1. The calculation of the variable limit assumes generate_fifo()
generates one output sample from every input byte. This is correct
for the raw mode, but not for the CD-XA BRR mode. This mode
generates 28 output samples from 15 input bytes. This is the
reason for the stuttering end of a CD-XA BRR mode sound. Every
generate_fifo() call generates approximately only half of the
possible samples when the fifo bytes are running low.
2. generate_fifo() doesn't generate the last output sample from
a CD-XA BRR mode sound. The last sample is generated from internal
state and the code will not be called without at least one byte
in the fifo.
3. It's not necessary to wait for a complete 15 byte packet in
CD-XA BRR mode. Audio playback devices should write all
requested samples immediately if possible.
4. The saturation function in CD-XA BRR mode works with 16 bit
integers. It should saturate at +32767 and -32768.
Since I think a few lines of code explain the issues better
than my words, I've attached a patch below.
With best regards,
Volker