Hi all,
I'm currently trying to modify the MESS source so that it's QL driver
supports floppies by emulating the Trump Card. I have the actual disk
access working and am able to access and load files from an image of a
QL disk.
However the emulated card will only see 640K of memory, I have managed
to work out that the trump card plays some tricks with memory mapping.
It seems initially the ROM is mapped in to both $C0000 and $10000, the
QDOS start up routine finds the rom at $C0000, and calls it's
initialisation routine at $C011E, which promptly does a jump to $10124,
and continues execution from there. It seems that the trump card
hardware maps out the copy of the ROM at $C0000, and maps the RAM into
that area on any read from the $10000-$17FFF area.
This means that the QDOS ram test only finds ram up until $BFFFF, and so
sets it to 640K (in the emulation). On the real machine it finds the
full 896K, so must be finding RAM in the $C0000-$FFFFF area, so the
trump card hardware must initially allow access to the RAM, before the
ROM is mapped in, but I have no clue as to how this is achieved.
Does anyone have any clues, or better still know how it actually works ?
I have started tracing the trump cards circuitry, but there are two
programable logic chips (PAL1 and PAL2v2), which though I have dumped,
when I decompile them the logic makes no sense to me :( Has anyone
worked out the logic for these ? Next step I guess will be to hook up
the PALs to a microcontroler and probe all combinations of inputs and
record outputs.
Cheers.
Phill.
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