uboot SPL Overview

Introduction:

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The idea is to build a mini u-boot(same as UBL in Davinci?) out of the u-boot tree that fits into SoC's internal SRAM (<=64K) and bootloads the real u-boot into the SDRAM, then the real u-boot will load the kernel into the SDRAM and boot it. :-).

Such a mini u-boot is typically called SPL(Second Program Loader) in u-boot terminology.

Duty of SPL:

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1> Basic ARM initialization

2> UART console initialization

3> Clocks and DPLL locking (minimal)

4> SDRAM initialization

5> Mux (minimal)

6> BootDevice initialization(based on where we are booting from.MMC1/MMC2/Nand/Onenand)

7> Bootloading real u-boot from the BootDevice and passing control to it.

BTW:

TI's X-loader is just one implemention of SPL out of the u-boot tree, And it depends on the u-boot source tree. same framework with u-boot. The u-boot guys will implement their own SPL in the tree. and then our system will boot without x-loader's help. :-)

Reference:

http://lists.denx.de/pipermail/u-boot/