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