Skunkboard RAM

[Songbird]

How much physical RAM is included on a Skunk? I ask because I was debugging a program that seemed to run fine on Skunk but not at all on VJ, and finally realized that I was overflowing my BSS section beyond $200000. RLN didn't flag it as a warning, so I've been happily running programs on Skunk without realizing my mistake.

[+CyranoJ]

None. Skunkboard ROM starts at $800000 just like a normal cart. You don't get any extra RAM.

[Songbird]

I suppose that makes sense, since Skunk should only be emulating the ROM space. So I wonder if the Jaguar HW auto-wraps an access above $200000 back to low RAM? Because it was weird for my program to be working properly on Skunk when I was overflowing BSS by several hundred KB.

[+CyranoJ]

Try writing to $200100 and see if pad input gets changed?

[ggn]

First of all, rln's only job is to combine object files together and perform any fixups needed. From what I remember it contains 0 jaguar specific code apart from the output formats (but then again COFF is a fairly common format).

 

As for your question, my guess would be that writing anything between the 2 and 8 megabyte space is simply ignored. You won't get a bus error or anything, so you can knock yourself out writing or reading to that address space but you'll either get garbage or some fixed pattern (zero I'd say).

 

A way to check would be something like cj suggests, set up an object that is displayed per frame in ram and start filling addresses $200000+object's data address. So if you object's graphics data start at $6000, go for $206000.

[SCPCD]

[$000000, $200000[ = [$200000, $400000[ as it's in the same bank of DRAM and the memory controller will probably wrap (to be checked, but it's what I remember from my test 18years ago)

[$400000, $800000[ is another bank of DRAM that is not used on the Jaguar and will always return "FFFFFFFF" (as there are pull-ups on the bus).

Edited May 5, 2019 by SCPCD