[U-Boot-Users] set up stack before board_init_f() on ppc440 core?

[Shawn Jin <shawnxjin@gmail.com>]

Hi,

I'm experimenting to set up the initial stack in DCACHE instead of the
internal SRAM on Ebony. In our SoC, no internal SRAM is available.

After reading README's <initial stack, global data> section and the
sample code of ppc405 which sets the stack in DCACHE, I understand the
ideas behind using DCACHE to be the initial stack. Well, I guess.
1. The CFG_INIT_RAM_ADDR is set to an address which nobody uses it.
2. Enable that area cacheable and all others are cache inhibited.

So I did several changes on cpu/ppc4xx/start.S,
include/configs/EBONY.h, and board/ebony/init.S, trying to set up the
stack correctly.
1. changed CFG_ISRAM_BASE to 0x40000000, whose original value is 0xc0000000.
2. commented out ISRAM setting in start.S
3. changed the TLB entries for ISRAM to the following.

#ifndef CFG_440_NO_ISRAM
    tlbentry( CFG_ISRAM_BASE, SZ_4K, 0x80000000, 0, AC_R|AC_W|AC_X )
    tlbentry( CFG_ISRAM_BASE + 0x1000, SZ_4K, 0x80001000, 0, AC_R|AC_W|AC_X )
#else
    tlbentry( CFG_ISRAM_BASE, SZ_256M, 0x40000000, 0, AC_R|AC_W|AC_X )
#endif

However these changes are not successful. A machine check exception
occurs when setting up the stack (2nd stwu). What am I missing here?

	/*----------------------------------------------------------------*/
	/* Setup the stack in internal SRAM or DCACHE */
	/*----------------------------------------------------------------*/
	lis	r1,CFG_INIT_RAM_ADDR at h
	ori	r1,r1,CFG_INIT_SP_OFFSET at l

	li	r0,0
	stwu	r0,-4(r1)
	stwu	r0,-4(r1)		/* Terminate call chain */

Thanks a lot,
-Shawn.