GX4000 ROM Address?

[SainT]

Hello!


Could someone tell me how the GX4000 boots from ROM? Does the first page get mapped to 0 and executed, or is it a different page and / or address? From disassembling Burnin' Rubber, mapping and executing the first page doesn't seem to make sense...


I'm looking at making an SD card driven SRAM cartridge for the GX4000 / Plus and need some info on how it boots!


Thanks!
SainT

[arnoldemu]

welcome Jim.

[fano]

It boots at address 0 of the cartridge ROM mapped on CPC lower rom (0->3FFF)
Good luck for your project seems very interesting.


This is the boot sequence of BR , what seems wrong for you ?

Code Select Expand

org #0000
di
ld bc,#df84
out (c),c
ld bc,#7f80
out (c),c
jp #c000


Burning Rubber may be confusing as it jumps directly to ROM page 4 (#80+4) as it located there like on 6128/464 Plus , the ROM pages 0 to 3 are normaly used for firmware and amdos.

[SainT]

Eurgh, that's weird. Last time I looked at the disassembly I could have sworn the last jp command was jp 0 giving and endless loop mapping the upper and lower roms. Now I look at it again, it makes far more sense! D'oh, oh well.


And hello, Kev! Tried getting hold of you on Facebook, but it looks like you use it about as much as I do! Its been a while...

[arnoldemu]

Eurgh, that's weird. Last time I looked at the disassembly I could have sworn the last jp command was jp 0 giving and endless loop mapping the upper and lower roms.

it's age catching up with you

And hello, Kev! Tried getting hold of you on Facebook, but it looks like you use it about as much as I do! Its been a while...

yeah, I don't use it much, but I've replied