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diff --git a/doc/README.korat b/doc/README.korat new file mode 100644 index 00000000000..0a59f4088a7 --- /dev/null +++ b/doc/README.korat @@ -0,0 +1,51 @@ +The Korat board has two NOR flashes, FLASH0 and FLASH1, which are connected to +chip select 0 and 1, respectively. FLASH0 contains 16 MiB, and is mapped to +addresses 0xFF000000 - 0xFFFFFFFF as U-Boot Flash Bank #2. FLASH1 contains +from 16 to 128 MiB, and is mapped to 0xF?000000 - 0xF7FFFFFF as U-Boot Flash +Bank #1 (with the starting address depending on the flash size detected at +runtime). The write-enable pin on FLASH0 is disabled, so the contents of FLASH0 +cannot be modified in the field. This also prevents FLASH0 from executing +commands to return chip information, so its configuration is hard-coded in +U-Boot. + +There are two versions of U-Boot for Korat: "permanent" and "upgradable". The +permanent U-Boot is pre-programmed at the top of FLASH0, e.g., at addresses +0xFFFA0000 - 0xFFFFFFFF for the current 384 KiB size. The upgradable U-Boot is +located 256 KiB from the top of FLASH1, e.g. at addresses 0xF7F6000 - 0xF7FC0000 +for the current 384 KiB size. FLASH1 addresses 0xF7FE0000 - 0xF7FF0000 are +used for the U-Boot environmental parameters, and addresses 0xF7FC0000 - +0xF7FDFFFF are used for the redundant copy of the parameters. These locations +are used by both versions of U-Boot. + +On booting, the permanent U-Boot in FLASH0 begins executing. After performing +minimal setup, it monitors the state of the board's Reset switch (GPIO47). If +the switch is sensed as open before a timeout period, then U-Boot branches to +address 0xF7FBFFFC. This causes the upgradable U-Boot to execute from the +beginning. If the switch remains closed thoughout the timeout period, the +permanent U-Boot activates the on-board buzzer until the switch is sensed as +opened. It then continues to execute without branching to FLASH1. The effect +of this is that normally the Korat board boots its upgradable U-Boot, but, if +this has been corrupted, the user can boot the permanent U-Boot, which can then +be used to erase and reload FLASH1 as needed. + +Note that it is not necessary for the permanent U-Boot to have all the latest +features, but only that it have sufficient functionality (working "tftp", +"erase", "cp.b", etc.) to repair FLASH1. Also, the permanent U-Boot makes no +assumptions about the size of FLASH1 or the size of the upgradable U-Boot: it is +sufficient that the upgradable U-Boot can be started by a branch to 0xF7FBFFFC. + +The build sequence: + + make korat_config + make all perm=1 + +builds the permanent U-Boot by selecting loader file "u-boot.lds" and defining +preprocessor symbol "CONFIG_KORAT_PERMANENT". The default build: + + make korat_config + make all + +creates the upgradable U-Boot but selecting loader file "u-boot-F7FC.lds" and +leaving preprocessor symbol "CONFIG_KORAT_PERMANENT" undefined. + +2008-02-22, Larry Johnson <lrj@acm.org> |