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@ytm@social.linux.pizza
2024-03-22 09:09:40

This is an idea of expanding 1541 memory (RAMBoard) with a twist.
Extra 8K of RAM is enough to hold a whole track. Last year I have already patched 1571 ROM to read whole track in one disk revolution and use that RAM as cache. 1571 has plenty of unused ROM space, but for 1541 I need more than available 16K.
The idea is to have RAM in $80-$9FFF and ROM in $A0-$FFFF. Maybe that extra ROM space could be used for lookup tables to speed up GCR decoding too.

Initial schematic design for a 1541 drive RAMBoard with some changes: 1) there is 32/64K ROM with 32K banks to be selected via a switch (ROM_A15) 2) optionally another switch for ROM_A14 can double the selection to choose 1 out of 4 possible 16K ROM banks (negating the next point) 3) memory layout should be that $8000-$9FFF is RAM, $A000-$FFFF is ROM; it's up to ROM_A14 to decide if $A000-$BFFF area comes from ROM (24K of ROM) or from mirrored 16K bank 4) RAM itself is a 32K chip (hard to buy a…

GitHub - ytmytm/1571-TrackCacheROM: A firmware patch for Commodore 1571 drive and internal C128D drive enabling RAM expansion use for track cache
A firmware patch for Commodore 1571 drive and internal C128D drive enabling RAM expansion use for track cache - ytmytm/1571-TrackCacheROM