AMD Elan SC520 development board linux 2.4.x boot problem

Hi all,

There may be folks using the AMD SC520 processor (and their development board from AMD) or thinking of using it. Thought that I would share some issues I had with it trying to setup MTD w/ JFFS on it. It may save someone hours of debugging.

The CDP (Customer Development Platform -as AMD calls it), boots all the 2.2.x kernels fine. It will NOT boot the 2.4.1 kernel out of the box. It just hangs after printing "Uncompressing Linux....Ok, Now booting the Kernel".

Upon further investigation (which involved downloading, building and trying about 12 previous kernels) and endless hours of digging through asm code, I've found the following:

Booting broke going from 2.3.22 to 2.3.23.

The problems seems to be in the e820 bios reported memory map. Any kernel after 2.3.22 just hangs trying to map the memory reported by the general software BIOS on the board.
One "easy" way to bypass this is to tell the kernel how much memory the system has- with the "mem=<your memory size here>M" option. The kernel then just ignores the e820 memory map and goes with what you tell it.

Another way (if you cannot pass kernel boot time options because of some special way you'r booting the kernel) is to hack the arch/i386/kernel/setup.c file to only loop thrice in reading the e820 memory may, while trying to map that memory.

The system just boots fine after that.

Hope that helps someone out there.

Now on to the (more ?) difficult task of trying to setup mtd and jffs on the system :)

Vipin Malik
Daniel Industries
Houston, TX.

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