Re: mac68k built-in video (PR#58164)

[Stan Johnson <userm57%yahoo.com@localhost>]

Update:

On 6/4/24 12:12 PM, Stan Johnson wrote:
> Hi David,
> 
> On 6/4/24 9:56 AM, David Brownlee wrote:
>> ...
>>
>> If you have time it would be great to track down the point of breakage.
> 
> I'll see what I can find.
> ...

I think I was wrong. Nubus video apparently has never worked on the Mac
IIci, except possibly if a RAM based video (RBV) monitor is used with an
unaccelerated Nubus video card installed (e.g. Toby frame buffer). Some
early kernels (see below) might also work if Nubus video is used but a
second (unused) monitor is connected to RBV.

I tried the following installation kernels:

1) 1.4.3 (1.4 MB MID_M68K)
   Using RBV with Toby frame buffer card installed:
     MacOS sees RBV and Toby card.
     NetBSD installation kernel sees internal video and Toby card (it
doesn't crash as later 9.x and 10.0 installation kernels do)
   Using a Toby frame buffer card, with no internal video:
     MacOD sees only the Toby card video
     NetBSD sees that there is no internal video, but it panics on the
serial console with "Cannot work with current memory mappings."

2) 1.6 (1.4 MB ELF)
   Same as 1.4.3; panic using Toby card and no RBV with message "Cannot
work with the current memory settings."

3) 2.0 and 4.0 (both 1.4 MB ELF) had the same results as 1.6.

I also tried a few later kernels (8.0 and 8.3) that seem to crash in the
same way as the 9.x and 10.0 installation kernels.

For Nubus video to work, NetBSD would have to act like MacOS; i.e. after
confirming that the system is a IIci (or IIsi), then check to see if
there is a monitor attached to RBV. If there is not, then treat the
system just like any other Mac II (i.e. use Nubus video and all of the
memory in Banks A and B is available). If there is a monitor attached to
RBV, then allow for internal video as well as Nubus video, and ignore
all of the memory in Bank A (or the first 1 MiB if Bank A has more than
1 MiB).

Of course, as a non-developer of NetBSD, that's easy for me to say.

I could try using the Traditional Installation Method to install the
latest version of 4.x and see if it works if I'm using Nubus video but
also have an unused monitor connected to RBV. I have a hunch that that
might work, but it wouldn't solve the real issue, which is that NetBSD
needs to ignore RBV altogether if there is no monitor attached to RBV.

I could also give up and just use RBV. If anyone is interested in
further testing, I can try other options or kernels; otherwise, I guess
this problem turns into an enhancement request to add the required
functionality.

thanks

-Stan