Q ? Will I need new ROMs?
A ? I don?t see why you would, the system will think it has a true 68k CPU at its heart so you won?t need new ROMs and I?m betting a lot of your existing hardware will work also including the new PPC on a PCI card for the A4000.
I can tell you absolutely positively without a doubt that you can't depend on the normal Amiga add on ROM method like you told me you planned to do. I researched this before (lord knows I didn't want to rewrite the ROM) and found it wouldn't work.
I just verified my findings to be sure before saying anything.
Look at the Exec 1.2 dissasembly on Aminet. The startup code that looks for the add on ROM executes an illegal Coldfire instruction before the jump to the new ROM.
If you don't believe me check address FC00F4. The very instruction that tests for the ROM isn't legal on any Coldfire cpu.
The existing ROM checks for an add on ROM like this:
FC00F4 cmp.w #$1111,(A1) ; If "1111" not found at F00000, then
FC00F8 bne.s FC00FE ;continue running below, else start
FC00FA jmp 2(A1) ; Jump to add on ROM
With portasm configured for the coldfire V4 this:
cmp.w #$1111,(A1)
translates to this:
move.w (a1),d0
cmp.w #0x1111,d0
I haven't decoded the 3.1 ROM but it is likely that it would test for an add on ROM in the same way.
At least some sort of patch to the existing ROM is needed and there are ways to do it and keep the existing ROM.
Did I mention that accessing the ROM through an accellerator port is slower than FLASH on the accellerator?
The solution I came up with was to make the standard Amiga ROM appear at a different address in memory so the initial FLASH startup code could copy it to flash, patch it and restart. The patch would jump to the add on ROM code and skip the test completely. I suggested this in July of last year. An alternative was to use a V4e part, copy the ROM to RAM, patch it there and run it from RAM.
Like I said, I spent a lot of time on this.
