uboot SPL Overview

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本文介绍了如何构建一个小型u-boot，使其能够从SoC的内部SRAM启动，并最终将真正的u-boot加载到SDRAM中进行引导。重点覆盖了SPL（Second Program Loader）的职责，包括基本的ARM初始化、UART控制台初始化、时钟和DPLL锁定、SDRAM初始化、总线配置、根据启动设备初始化以及从启动设备加载并传递控制给真正u-boot的过程。

转载自http://blog.youkuaiyun.com/abc47bca/article/details/6306005

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/