On 11.10.2021 1:47, Louis Ohland wrote:
> Please do. It makes me curious, blue. What is this PAL doing? Is it
> memory? Wired to the FDC, that doesn't seem quite sensible.
Why not? The PAL is sitting right next to the FDC and at least some of
the traces go towards the controller.
> Does it add function? DSKBOOT seems to suggest something related to
Yeah... the name. The "DSK" part makes sense - floppy DiSK, DBA DiSK -
could be either (or both) if we go just by the name itself.
> not sure it is O/S related, more like IML? Maybe DSKBOOT supports DBA-ESDI?
That's the thing, everything related to the OS "BOOT" process is handled
in software/firmware. I can't think of anything boot-related that would
require a special HW logic.
The only IML-related thing that requires a special HW is the
E0000-FFFFFh range ROM/RAM switching, but that's implemented on the
> You must.. probe it! Yes!
> What pins of the FDC does it connect to? What other components does it
> connect to?
Yep... Probulation time!
> How about this for an unsupported rumor... the DSKBOOT connects the FDC
> to NVRAM to enable booting from CDROM... ;)
:-D I like the enthusiasm, but that doesn't make much sense. The two
components are already connected to the planar I/O bus. Not because they
need to talk to each other directly, but because the CPU needs to be
able to address both of them.
Going by the little information we have currently, I only have one
theory - the PAL handles the FDC reset initialization. The 82077
controller can be switched between 3 different modes (PC AT, PS/2, and
Model 30). This is done by setting two of the inputs in a certain way
when the RESET line is toggled. I'll have to check the datasheet again,
but I don't think this can be achieved with high value pull-up or
something similar in this particular case. So perhaps "DSKBOOT" means
"DiSK controller BOOT"? Though something like "FDCINIT" would make much
sense in this context...