[U-Boot-Users] 8540 and L1 cache mapping

[Kumar Gala]

On Jun 30, 2005, at 10:13 AM, Charles J Gillan wrote:

> Recently I have been studying the boot sequence for the 8540 based  
> boards
> in U-Boot. I have a question on the location of the initial C stack.
>
> As I understand it,
>
>        cpu/mpc85xx/start.S
>
> uses L1 data cache as the location for the C stack prior to the  
> relocation
> into RAM.
>
> CFG_INIT_RAM_ADDR is defined within the relevant "config" file for  
> each 6540
> based board.
>
> I see in the 8540 User Manual that there is a register which can be  
> used to
> position L2 cache in physical address space but there does not  
> appear to be
> a similar register for L1 cache.
>
> However, I see that in the init.S files, for each board, entries  
> are placed
> into TLB0 for memory at address CFG_INIT_RAM_ADDR. This is declared as
> cacheable and non-garded.
>
> Am I correct in thinking that this is all that is required to position
> the C run-time stack in L1 D-cache ?

That should be it.  We decided to use the L1 cache and lock lines  
into it for the initial C stack since we know that the L1 cache would  
always be there on an e500 core and were not sure if the L2 would be  
available.

- kumar