What is in ram below $4000

[toarnold]

Hello,

 

is someone out there who can tell me, why user ram starts at $4000? I think ram below $4000 is used by the boot rom, but after boot the cartridge takes places - what happens in this area than?

 

Greetings,

toarnold

 

[+CyranoJ]

There be dragons!!!

 

It's all a myth.

 

The CD Bios will install below $4000 and keep a copy of the CD TOC. The MemoryTrak BIOS also installs below there.

 

If you aren't using either, its all free! free I tells you! (apart from the exception vectors)

 

(Rebooteroids uses it!)

[Seedy1812]

If you are using a skunkboard to read in files from a pc then memory below $4000 is used

; getBothBuffers - waits for both buffers to be free then returns the
; first buffer ($1800) in d1. Returns 0 in d1 if both buffers do not free up.
 
; checkBuffer1 - test if buffer 1 is available (returns in d1)
checkBuffer1:
	move.l #($1800+$FEA),d1
	jmp checkbuffer

; checkBuffer2 - test if buffer 2 is available (returns in d1)
checkBuffer2:
	move.l #($2800+$FEA),d1
	jmp checkbuffer

 

Edited May 15, 2017 by Seedy1812

[Tursi]

If you are using a Skunkboard at all then memory below $4000 is used - the Skunkboard runs most of its BIOS there Check boot.s for the details, it only uses a little bit of it.

 

The $1800/$2800 buffers used for communication with the PC are in the Cypress USB controller's RAM, not Jaguar RAM.

[+CyranoJ]

If you are using a Skunkboard at all then memory below $4000 is used - the Skunkboard runs most of its BIOS there Check boot.s for the details, it only uses a little bit of it.

 

The $1800/$2800 buffers used for communication with the PC are in the Cypress USB controller's RAM, not Jaguar RAM.

 

But that is only during the upload phase. Once it's running, unless you want to use the console/IO functions, it can be killed off, right?

[Tursi]

 

But that is only during the upload phase. Once it's running, unless you want to use the console/IO functions, it can be killed off, right?

 

Yeah, as long as you never want to return to the Skunk BIOS (using RTS), or use its functions, then you don't need to preserve that data.