Porting LinuxBIOS to the AMD SC520: A Follow-up Report

Getting the board Flashed led to some interesting detective work for the LANL team.
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MMCR can be moved...

AndrewD's picture

Quote:
"Probably the single biggest problem is the location of the configuration registers, placed right in the middle of the top 2MB of memory"

You can map the MMCR to any 4k offset in the lower 1G by writing to the CBAR register. 0xFFFEF000 is just the default location, so I would not see that as a flaw.

I ended up using rolo instead of Linuxbios on a SC520 based product I designed a few years ago. U-boot is another very powerful option, but they are both more targeted to embedded products.

MMCR can be moved ... but not removed.

Stefan Reinauer's picture

The problem in this case is that even if you "move" the MMCR, it is still sitting at its old position 0xFFFEF000, in addition to the new one.

Code sample

Craig Ringer's picture

The code snippet is broken - presumably due to mangling by a CMS. Given the extreme difficulty I'm having in getting this godawful commenting system to not mangle these code snippets, that's my working theory. LJ staff, please fix your CMS so it doesn's strip spaces in >code<>/code< blocks! I had to use   in a >code<>/code<block, which is (a) gross and (b) should probably not be interpreted as an entity, but rather as a literal.

In addition to the total loss of indenting, I found two other problems. First:


bios = mmap(0, size, PROT_READ, MAP_SHARED, fd_mem,
off_t) (0xffffffff - size + 1));

looks like it should be:


bios = mmap(0, size, PROT_READ, MAP_SHARED, fd_mem,
           (off_t)(0xffffffff - size + 1) );

and:


#include #
include

should evidently be:


#include
#include

With those changes it builds OK here. The dump doesn't look too interesting on this system - probably not a flash image, anyway - but it's an AMD64 box so it's quite likely the flash is mapped to somewhere different. Any idea what address it might be at?

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