Bug in genesis.c?

[HardWareMan]

...i do know the officials documents said we must write the last command from RAM...

Official docs says:

The final write must use the work RAM. There are two ways to accomplish this:
1. by copying the DMA program into RAM, or
2. by doing a final "move.w RAM_address,$C00004"

So, opcode it self no need to be in RAM, but operand wich must be writen in $C00004 must be in RAM. But, I am already used "move.w ROM_address,$C00004" and all works fine. I think this some how connected with hardware limitation: cartrige can be written by byte but can be read only by word and RAM can be reading or writting by byte or word. Or something like that.

[notaz]

I've checked what commercial games do again, and they use register, immediate values or RAM as their source operand. Here are some examples:

Code: Select all

move.w  $f640.w, (A5) ; a5=00c0000
move.w  D0, (A4)      ; a4=00c0000
move.w  (A1)+, (A0)   ; a0=00c00004, a1=ffffe4be

There are some games (mostly Konami) which only use RAM, but many others like to use immediates and registers. Perhaps what the docs wanted to say is that we should not use ROM -> c00004 move on the instruction which activates DMA (none of the games I tested do that).