From PlugWiki

The ArcNumber parameter references a particular mach-type/machine from the kernel's Arm' machine table, telling the kernel which specific piece of hardware its on. Its presumed that the bundled kernel is hardcoded and doesnt need this parameter, but if you are building your own kernel, you need to set this parameter in uBoot so the kernel knows what to boot. Leaving it set appears to be perfectly OK for botting the bundled kernels.

Its value is 2097 for SheevaPlug, 2325 for OpenRD-Base, and 2361 for OpenRD-Client.

kernel

In the kernel, ARM has a table defining all the arm machines. Its located at arch/arm/tools/mach-types. You can update it to the latest with:

wget http://www.arm.linux.org.uk/developer/machines/download.php -O arch/arm/tools/mach-types

marvell git & missing mach's

Presently, Aug 22 2009, Marvell's git tree contains an out of date arch/arm/tools/mach-types file. This causes the kernel to fail to build, as the tree uses definitions for machine types non existant in their old mach-types file. The result is this:

  CC      arch/arm/mach-kirkwood/openrd_base-setup.o
arch/arm/mach-kirkwood/openrd_base-setup.c:75: error: âMACH_TYPE_OPENRD_BASEâ undeclared here (not in a function)
make[2]: *** [arch/arm/mach-kirkwood/openrd_base-setup.o] Error 1

Oh noes!

Fear not brave bleeding edge soldier; just follow the instructions in [[[#kernel]]] to update your mach-types and ye shall be saved. Happy compiling.