VIC20 for the MiST fpga (part 2)

Found a few minutes today to have a look at the cartridge system. As it was implemented the vic didn’t start the rom when doing a reset. As found in the documentation linked in the previous post the vic expects some magic bytes at a specific address to autostart a cartridge:

It looks like that those dumped roms (.prg) have two extra bytes in the beginning. Shifting the access to those roms two bytes up made it work:



Solar System

As usual the source code can be found in my github repository.

Update 07.12.2014
Looks like that there’re different dumps available. Found a side with .a0 cartridges which doesn’t need the shift.

2 thoughts on “VIC20 for the MiST fpga (part 2)

  1. With the two extra bytes the rom should actually ve loadable as a prg. These two bytes contain the target address which should be a000 for a cartridge.

  2. WiSo says:

    Figured that later on. It seems to be that there are cartridge ROMs with load address and without. The current implementation expects .crt ROMs without load address.
    I’ll have a look at the TOSEC crt dumps to see what format they are and will adapt the vic to it.

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