Richard Danter wrote:
Hi all,
Further progress on my port. I can now write to flash!
I noticed in lib_ppc/board.c board_init_r() that on e500 CPU's the unlock_ram_in_cache() function is called. The 7xx/74xx also locks the init RAM in the dcache, but nowhere is it unlocked.
I tried calling unlock_ram_in_cache() from my board's misc_init_r() function, but this crashes U-Boot.
As an experiment, I left the cache locked, but then ran the "dcache off" command from the shell. If I do printenv before turning the dcache off it is all OK, if I do it after then it crashes.
With my debugger I can see that the gd data structure is garbage when env_get_char_memory() is called. But I thought all data was copied to the main sys RAM.
Is there something else I need to do before/after calling unlock_ram_in_cache() so I can use the D-Cache as normal?
Thanks Rich
PS Calling icache_enable() from misc_init_r() seems to work fine.
WRT data cache enabling, in order to enable data cache, you need to first set up BATs and/or the MMU page tables. You need the MMU configured and enabled so that you can mark I/O space(s) to be uncached... by default every data access is cached which wreaks havoc with I/O (to put it lightly :-).
I am not aware of anybody doing this in u-boot because it is a major pain to do and minor benefit for the brief time you should be running in u-boot (but likely someone has).
When you boot your OS (e.g. linux), the OS should do its own MMU set up and data cache enabling.
WRT your locking question, I don't know.
gvb