MPC8347/9 stack in cache (CFG_INIT_RAM_ADDR)

Hi all,

I am trying to get U-Boot running on a custom MPC8347 board, and am having difficulty with the start-up code. I'm running essentially with U-boot 1.1.6, which has had the ppc83xx code updated to U-Boot 1.2. I'm running out of SDRAM, with CFG_RAMBOOT

I have set CFG_INIT_RAM_ADDR to 0xFB000000, a location un-mapped by any of the windows or chip select settings, but mapped into a BAT by the board config:

#define CFG_IBAT6L  (0xFB000000 | BATL_PP_10  | BATL_MEMCOHERENCE)
#define CFG_IBAT6U  (0xFB000000 | BATU_BL_64M | BATU_VS | BATU_VP)

#define CFG_HID2 HID2_HBE // to enable high bats
#define CFG_INIT_RAM_LOCK 1

in cpu/mpc83xx/start.S when it gets to the point of using the stack-in-cache

----start.S
/* set up the stack pointer in our newly created
* cache-ram (r1) */
lis r1, (CFG_INIT_RAM_ADDR + CFG_GBL_DATA_OFFSET)@h ori r1, r1, (CFG_INIT_RAM_ADDR + CFG_GBL_DATA_OFFSET)@l

li r0, 0 /* Make room for stack frame header and */
stwu r0, -4(r1) /* clear final stack frame so that */
stwu r0, -4(r1) /* stack backtraces terminate cleanly */

----END start.S

It crashes badly at the first stwu instruction. I get strange behaviour, all register settings in debugger (green hills probe) showing 0x43 - and a grinding halt.

My understanding is that to get some ram for the initial stack on these processors, it's necessary to use the RAM-in Cache, you should map an unused area of address space into a BAT, but am not certain of other requirments such as BAT properties, or settings?

Is anyone more familar with this or suggestions?

thanks,

Matt

Well, I should be more familiar, since I wrote the support for the MPC8349E-mITX, but honestly I just diddled with the values until I got something working.

Have you taken a look at the latest MPC8349ITX.h? I went through a lot of effort to make that file as "intelligent" as possible.

I have this:

#define CFG_INIT_RAM_ADDR 0xFD000000 /* Initial RAM address */

/* SDRAM @ 0xF0000000, stack in DCACHE 0xFDF00000 & FLASH @ 0xFE000000 */
#define CFG_IBAT6L (0xF0000000 | BATL_PP_10 | BATL_MEMCOHERENCE)
#define CFG_IBAT6U (0xF0000000 | BATU_BL_256M | BATU_VS | BATU_VP)

Maybe you BAT window is too small?

Timur Tabi
Linux Kernel Developer @ Freescale