the screen was slightly garbled

Compared to what? Real system or bochs bios only? (vgabios/elpin?)
Do you have some small sample of this problem?

wd wrote:

the screen was slightly garbled

Compared to what? Real system or bochs bios only? (vgabios/elpin?)
Do you have some small sample of this problem?

I have tried exclusively in Bochs, see attached pictures. However, I'm pretty sure that only enabling planes 0 and 1 is actually correct, as those are the only planes written to (0 = characters, 1 = attributes). It is possible however, that enabling all planes works for VGA as well, depending on how the odd/even chaining is rigged up in hardware.

JAL

Well the bios is quite "destructive" with the font functions, so it could actually
be correct that it (real vga bios) doesn't care about setting/restoring the
correct plane setting.
Got to look up how some other bioses handle this...

ibm vga stuff:

1seg001:123A                 mov     dx, 3C4h
2seg001:123D                 mov     ax, 302h
3seg001:1240                 out     dx, ax

So 3 it seems for those.

wd wrote:

ibm vga stuff: […]
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ibm vga stuff:

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1seg001:123A                 mov     dx, 3C4h
2seg001:123D                 mov     ax, 302h
3seg001:1240                 out     dx, ax

So 3 it seems for those.

It is what I expected, as it makes sense that only planes 0 and 1 are enabled, since these are chained. Allowing access to 3 and 4 (where the character definitions reside) doesn't make too much sense.

JAL

Well they could have saved/restored the values, too, but guess they
assumed strict default-textmode thus used those fixed values.
S3 does the same btw.

wd wrote:

Well they could have saved/restored the values, too, but guess they
assumed strict default-textmode thus used those fixed values.
S3 does the same btw.

Ok, so Dosbox should do the same then I guess.

JAL