MacOS (un)helpfully leaves the FIFO engine running even when all the samples have
been written to the hardware, and expects the FIFO status flags and IRQ to be
updated continuously.
There is an additional problem in that not all audio backends guarantee an
all-zero output when there is no FIFO data available, in particular the Windows
dsound backend which re-uses its internal circular buffer causing the last played
sound to loop indefinitely.
Whilst this is effectively a bug in the Windows dsound backend, work around it
for now using a simple heuristic: if the FIFO remains empty for half a cycle
(~23ms) then continuously fill the generated buffer with empty silence.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20231004083806.757242-9-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
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>
Message-ID: <20231004083806.757242-8-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
