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| author | Stefan Roese <sr@denx.de> | 2010-11-26 15:43:17 +0100 |
|---|---|---|
| committer | Stefan Roese <sr@denx.de> | 2010-12-17 09:43:36 +0100 |
| commit | f7b548adb56729f07cd5e96c10edc5260527d447 (patch) | |
| tree | 9dc1362889a903559ca77d407c34c89021a58bec /arch/powerpc/cpu/ppc4xx | |
| parent | cf1971c1c0a76c3105a347102db083027a3d7b91 (diff) | |
| download | u-boot-imx-f7b548adb56729f07cd5e96c10edc5260527d447.zip u-boot-imx-f7b548adb56729f07cd5e96c10edc5260527d447.tar.gz u-boot-imx-f7b548adb56729f07cd5e96c10edc5260527d447.tar.bz2 | |
ppc4xx: Clarify comment about boot chip-select in start.S
Ths old comment was quite screwed up. Replace it with a new version
that should be a bit more descriptive.
Signed-off-by: Stefan Roese <sr@denx.de>
Diffstat (limited to 'arch/powerpc/cpu/ppc4xx')
| -rw-r--r-- | arch/powerpc/cpu/ppc4xx/start.S | 26 |
1 files changed, 14 insertions, 12 deletions
diff --git a/arch/powerpc/cpu/ppc4xx/start.S b/arch/powerpc/cpu/ppc4xx/start.S index 0e75794..99822d7 100644 --- a/arch/powerpc/cpu/ppc4xx/start.S +++ b/arch/powerpc/cpu/ppc4xx/start.S @@ -48,21 +48,23 @@ *------------------------------------------------------------------------------- */ -/* U-Boot - Startup Code for AMCC 4xx PowerPC based Embedded Boards - * +/* + * Startup code for IBM/AMCC PowerPC 4xx (PPC4xx) based boards * - * The processor starts at 0xfffffffc and the code is executed - * from flash/rom. - * in memory, but as long we don't jump around before relocating. - * board_init lies at a quite high address and when the cpu has - * jumped there, everything is ok. - * This works because the cpu gives the FLASH (CS0) the whole - * address space at startup, and board_init lies as a echo of - * the flash somewhere up there in the memorymap. + * The following description only applies to the NOR flash style booting. + * NAND booting is different. For more details about NAND booting on 4xx + * take a look at doc/README.nand-boot-ppc440. * - * board_init will change CS0 to be positioned at the correct - * address and (s)dram will be positioned at address 0 + * The CPU starts at address 0xfffffffc (last word in the address space). + * The U-Boot image therefore has to be located in the "upper" area of the + * flash (e.g. 512MiB - 0xfff80000 ... 0xffffffff). The default value for + * the boot chip-select (CS0) is quite big and covers this area. On the + * 405EX this is for example 0xffe00000 ... 0xffffffff. U-Boot will + * reconfigure this CS0 (and other chip-selects as well when configured + * this way) in the boot process to the "correct" values matching the + * board layout. */ + #include <asm-offsets.h> #include <config.h> #include <asm/ppc4xx.h> |