Memory area 0xA8400000

[chrismulhearn]

On my 1.5 PSP, kernel-mode accesses to memory address 0xA8400000 give me a CPU data bus error. Anyone know why this is? Is this actually the VRAM, which is also accessible at 0xA4000000?

If its not the VRAM, is there any remedy to get access to that memory?

Note: I know that there is usually some library loaded in that location, but that doesn't matter because I'm not using the PSP OS and I've replaced their exception handler, so nothing should ever be trying to use that memory area.
Simply writing data to that location causes a bus error.

[jas0nuk]

Complete guess, but maybe this topic will help you:
http://forums.ps2dev.org/viewtopic.php?t=6800

[J.F.]

Hmm - using the info in that topic, it looks like you may be able to make uClinux use all 32M of memory, or at least be able to load and protect the uClinux kernel, much like the PSP kernel is protected.

[chrismulhearn]

sure can!

Just had to rewrite some parts of the bootloader to accomodate it [now that I am overwriting the PSP OS, I can't be writing the kernel to its final destination while loading it off the memory stick, so I load the kernel to an intermediate location first, then kill PSP OS entry, then copy the kernel to its real home. Then jump to it and enjoy the 32 megabytes of breathing room.]

Thanks guys, and thank you Tyranid, great find.

[J.F.]

Every bit helps. Going from 24M to 32M is a BIG increase.

[hagisbasheruk]

This is getting very exciting now thanks jas0nuk for the link and thanks to Tyranid for making the discovery regarding the memory protection bits.

[jas0nuk]

Ah, glad it helped :)