Hi,
Before board_init_f() is called, which is C code, a stack must be set up. The stack is usually set up in internal SRAM. Where shall I put stack in if I don't have an internal SRAM?
I read through cpu/ppc4xx/start.S and found some set up the temporary stack in DCACHE (Walnut 405 is an example). But the CFG_INIT_RAM_ADDR is 0x40000000, which is inside SDRAM. Why was it commented that the stack was set in DCACHE? I don't quite understand how a cache acts like RAM, i.e., a cache can be accessed by address xxxx_xxxx. Is a cache only accessible by special cache instructions? The following code is extracted from ppc4xx/start.S
#ifdef CFG_INIT_DCACHE_CS /*----------------------------------------------------------------------- */ /* Memory Bank x (nothingness) initialization 1GB+64MEG */ /* used as temporary stack pointer for stage0 */ /*----------------------------------------------------------------------- */ li r4,PBxAP mtdcr ebccfga,r4 lis r4,0x0380 ori r4,r4,0x0480 mtdcr ebccfgd,r4
addi r4,0,PBxCR mtdcr ebccfga,r4 lis r4,0x400D ori r4,r4,0xa000 mtdcr ebccfgd,r4
/* turn on data chache for this region */ lis r4,0x0080 mtdccr r4
Thanks, -Shawn.