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mac_via: make SCSI_DATA (DRQ) bit live rather than latched 

The VIA2 on the Q800 machine is not a separate chip as in older Macs but instead
is integrated into the on-board logic. From analysing the SCSI routines in the
MacOS toolbox ROM (and to a lesser extent NetBSD and Linux) the expectation seems
to be that the SCSI_DATA (DRQ) bit is live on the Q800 and not latched.

Fortunately we can use the recently introduced mos6522 last_irq_levels variable
which tracks the edge-triggered state to return the SCSI_DATA (DRQ) bit live to
the guest OS.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220305150957.5053-11-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
This commit is contained in:
Mark Cave-Ayland 2022-03-05 15:09:55 +00:00
parent d4454e41d7
commit 677a4725b1
1 changed files with 16 additions and 1 deletions
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17
hw/misc/mac_via.c
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@ -906,9 +906,24 @@ static uint64_t mos6522_q800_via2_read(void *opaque, hwaddr addr, unsigned size)
{
MOS6522Q800VIA2State *s = MOS6522_Q800_VIA2(opaque);
MOS6522State *ms = MOS6522(s);
uint64_t val;
addr = (addr >> 9) & 0xf;
return mos6522_read(ms, addr, size);
val = mos6522_read(ms, addr, size);
switch (addr) {
case VIA_REG_IFR:
/*
* On a Q800 an emulated VIA2 is integrated into the onboard logic. The
* expectation of most OSs is that the DRQ bit is live, rather than
* latched as it would be on a real VIA so do the same here.
*/
val &= ~VIA2_IRQ_SCSI_DATA;
val |= (ms->last_irq_levels & VIA2_IRQ_SCSI_DATA);
break;
}
return val;
}
static void mos6522_q800_via2_write(void *opaque, hwaddr addr, uint64_t val,