Re: [PATCH 15/30] asc: generate silence if FIFO empty but engine still running

["Volker Rümelin" <vr_qemu@t-online.de>]

> 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.
>
> Since not all audio backends guarantee an all-zero output when no data is
> provided, explicitly generate an all-zero output when this condition occurs to
> avoid the audio backends re-using their internal buffers and looping audio once
> the FIFOs are empty.
>
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
>   hw/audio/asc.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)

Reviewed-by: Volker Rümelin <vr_qemu@t-online.de>

> diff --git a/hw/audio/asc.c b/hw/audio/asc.c
> index 04194b1e43..c5173a8d35 100644
> --- a/hw/audio/asc.c
> +++ b/hw/audio/asc.c
> @@ -158,8 +158,10 @@ static int generate_fifo(ASCState *s, int maxsamples)
>       limit = MIN(MAX(s->fifos[0].cnt, s->fifos[1].cnt), maxsamples);
>   
>       /*
> -     * If starting a new run with no FIFO data present, update the IRQ and
> -     * continue
> +     * MacOS (un)helpfully leaves the FIFO engine running even when it has
> +     * finished writing out samples. Since not all audio backends guarantee an
> +     * all-zero output when no data is provided, zero out the sample buffer
> +     * and then update the FIFO flags and IRQ as normal and continue
>        */
>       if (limit == 0 && s->fifos[0].int_status == 0 &&
>               s->fifos[1].int_status == 0) {
> @@ -168,8 +170,9 @@ static int generate_fifo(ASCState *s, int maxsamples)
>           s->fifos[1].int_status |= ASC_FIFO_STATUS_HALF_FULL |
>                                     ASC_FIFO_STATUS_FULL_EMPTY;
>   
> +        memset(buf, 0x80, maxsamples << s->shift);
>           asc_raise_irq(s);
> -        return 0;
> +        return maxsamples;
>       }
>   
>       while (count < limit) {