[Qemu-devel] [PATCH] sb16: fix interrupt acknowledgement

[Paolo Bonzini <pbonzini@redhat.com>]

SoundBlaster 16 emulation is very broken and consumes a lot of CPU, but a
small fix was suggested offlist and it is enough to fix some games.  I
got Epic Pinball to work with the "SoundBlaster Clone" option.

The processing of the interrupt register is wrong due to two missing
"not"s.  This causes the interrupt flag to remain set even after the
Acknowledge ports have been read (0x0e and 0x0f).

The line was introduced by commit 85571bc (audio merge (malc), 2004-11-07),
but the code might have been broken before because I did not look closely
at the huge patches from 10 years ago.

Reported-by: Joshua Bair <j_bair@bellsouth.net>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/audio/sb16.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/audio/sb16.c b/hw/audio/sb16.c
index bda26d0..444eb9e 100644
--- a/hw/audio/sb16.c
+++ b/hw/audio/sb16.c
@@ -999,7 +999,7 @@ static IO_READ_PROTO (dsp_read)
         retval = (!s->out_data_len || s->highspeed) ? 0 : 0x80;
         if (s->mixer_regs[0x82] & 1) {
             ack = 1;
-            s->mixer_regs[0x82] &= 1;
+            s->mixer_regs[0x82] &= ~1;
             qemu_irq_lower (s->pic);
         }
         break;
@@ -1008,7 +1008,7 @@ static IO_READ_PROTO (dsp_read)
         retval = 0xff;
         if (s->mixer_regs[0x82] & 2) {
             ack = 1;
-            s->mixer_regs[0x82] &= 2;
+            s->mixer_regs[0x82] &= ~2;
             qemu_irq_lower (s->pic);
         }
         break;
-- 
2.1.0