On Sat, 27 Sep 2008, Brad Boyer wrote:
.. the ideal situation would be to get the real DMA working (the IIfx is
the only Mac using a 5380 chip that has real DMA) which would mean
treating it as a separate machine anyway. If you want the details, doing
PDMA on the IIfx requires poking the DMA engine to get it out of the
way. I have the docs someplace.
Docs would be nice... although I can't test anything as I don't have that
hardware. But aside from yourself, there's a user on the debian-68k list
who has a IIfx.
What are these unknown interrupts? DRQ? PDMA stalling?
The schematics say that only the NCR5380 drives that VIA input (VIA2
CB2 aka IRQ_MAC_SCSI), so IRQ 19 is definitely the IRQ line from the
chip (and not the DRQ line). The DRQ interrupt was/is never registered
(BTW, I found that it doesn't fire on one of the PowerBooks).
I don't think we really know where the DRQ line is connected, if at all.
The Guide to Mac Family Hardware says that IRQ and DRQ are connected to
the OSS. AFAICT, DRQ is wired to VIA2 CA2 on all machines that have
VIA2/RBV.
From looking at the NetBSD driver and The Guide, I think perhaps we're
using the wrong address for PDMA I/O on the particular powerbook that
didn't raise a DRQ interrupt. (The IIci memory map in The Guide shows
several different SCSI memory regions including "pseudo-DMA with DRQ" and
"pseudo-DMA, no DRQ".) Worst case, we'd have to poll DRQ in the status
register as per existing code.
That's actually the problem I had with getting the DMA on the IIfx
working. I never got the EOT interrupt from the DMA engine.
... that doesn't sound very promising.
The Guide says, "Using the SCSI DMA IC, only data transfers are handled by
the DMA channel; SCSI bus protocol is under the control of software
running on the main processor, just as it is on other Macintosh models.
The SCSI DMA IC on the Macintosh IIfx can also function as a conventional
SCSI interface and transfer data under the control of the main processor
... Existing drivers that don't use hardware handshaking will run on the
Macintosh IIfx as is. Drivers that do use hardware handshaking must be
modified to set up the SCSI DMA for hardware handshaking in order to run
on the Macintosh IIfx ... To initiate a DMA transfer, the SCSI driver
writes control information to the DMA address counter and DMA Byte Count
register on the SCSI DMA IC and then writes to one of the IC's start
registers."
There is no detailed programming information unfortunately. But to me, it
sounds like PDMA is not possible on the IIfx (there's also a comment in
mac_scsi.c to that effect) so it seems we either attempt DMA again or use
PIO (yuck).
Finn
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