From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shawn Jin Date: Fri, 25 Feb 2005 10:42:28 -0800 Subject: [U-Boot-Users] set up stack before board_init_f() on ppc440 core? Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de 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.