flying blind with BATs
Adrian Cox
apc at agelectronics.co.uk
Tue Oct 3 02:09:33 EST 2000
Tim Montgomery wrote:
> I have the BATs configure (by the bootloader) such that 0xc0000000
> (virtual) is mapped to 0x00000000 (phys SDRAM base), but after
> the image is decompressed (to the virtual addr), I get garbage when
> I do a dump at 0xc0000000 (i.e. the kernel isn't there.)
My trick is just to load the ELF file to physical address 0. The elf
file format is easy enough to decode (mine is about 60 lines of C, and
I'll post it if there's interest). Then, I load r3 with a value to
indicate machine type ('TPE3' or 'TPE4'), and jump to the start of the
kernel turning off the cache and MMU.
Important things to note are:
1) Flush the caches over the region you've just loaded before fiddling
with MMU and cache settings.
Here's the section of my bootloader - r3 is the kernel entry point
(physical address) and r4 is 'TPE3':
ppc_run_executable:
mtspr SRR0, r3
mr 3, 4
mfspr 9, HID0
li 10, HID0_DCE
andc 9, 9, 10
mtspr HID0, 9
sync
mfmsr 9
li 10, MSR_DR | MSR_IR
andc 9, 9, 10
mtspr SRR1, 9
sync
rfi
- Adrian Cox, AG Electronics
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