Not sure if this is the correct place to ask such a question, but here goes.
Ok so I mess around with an old 80's drum machine a lot. It's based around an old 8031 Processor Program code is stored on a 27c256 eprom and sound data is stored on 2 x 27c040 mask roms.
The 27c256 in this machine holds the OS and also the data table containing the names of the various drum sounds and the start addresses for each sample. and in this chip there is data either side of the table. I already make customised eproms for the machine, but I am limited to only 'replacing' the data in this table, which confines the machine to 47 different sounds.
I had an idea, and want to put it out to the heads to see if I'm talking rubbish or not..
The existing OS has quite a lot of space left at the end of the file (FF) Is it at all possible to hack the firmware so that at the point where it would read the table, insert the instruction to JUMP to another part of the firmware and read in a table that is larger in length with more samples etc. (lets say 100 sounds instead of 47 or something) and then at the end of this, JUMP back to where the end of the old table resides in code.
In essence I'm talking about bypassing a part of the code and replacing it with a larger piece. I know that of course I cant just make whats already there bigger as it would move the rest of the code, which as I understand would break then.
I'm currently replacing the data in the table by just patching the bytes that are already there.
Perhaps I'm talking jibberish, perhaps I'm not.