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Tom Rini71e68402012-02-20 13:27:43 +00001Overview of SPL on OMAP3 devices
2================================
3
4Introduction
5------------
6
7This document provides an overview of how SPL functions on OMAP3 (and related
8such as am35x and am37x) processors.
9
10Methodology
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12
13On these platforms the ROM supports trying a sequence of boot devices. Once
14one has been used successfully to load SPL this information is stored in memory
15and the location stored in a register. We will read this to determine where to
16read U-Boot from in turn.
17
18Memory Map
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20
21This is an example of a typical setup. See top-level README for documentation
22of which CONFIG variables control these values. For a given board and the
23amount of DRAM available to it different values may need to be used.
24Note that the size of the SPL text rodata and data is enforced with a CONFIG
25option and growing over that size results in a link error. The SPL stack
26starts at the top of SRAM (which is configurable) and grows downward. The
27space between the top of SRAM and the enforced upper bound on the size of the
28SPL text, data and rodata is considered the safe stack area. Details on
29confirming this behavior are shown below.
30
31A portion of the system memory map looks as follows:
32SRAM: 0x40200000 - 0x4020FFFF
33DDR1: 0x80000000 - 0xBFFFFFFF
34
35Option 1 (SPL only):
360x40200800 - 0x4020BBFF: Area for SPL text, data and rodata
Tom Rinie0820cc2012-05-08 07:29:31 +0000370x4020E000 - 0x4020FFFC: Area for the SPL stack.
Tom Rini71e68402012-02-20 13:27:43 +0000380x80000000 - 0x8007FFFF: Area for the SPL BSS.
390x80100000: CONFIG_SYS_TEXT_BASE of U-Boot
400x80208000 - 0x80307FFF: malloc() pool available to SPL.
41
42Option 2 (SPL or X-Loader):
430x40200800 - 0x4020BBFF: Area for SPL text, data and rodata
Tom Rinie0820cc2012-05-08 07:29:31 +0000440x4020E000 - 0x4020FFFC: Area for the SPL stack.
Tom Rini71e68402012-02-20 13:27:43 +0000450x80008000: CONFIG_SYS_TEXT_BASE of U-Boot
460x87000000 - 0x8707FFFF: Area for the SPL BSS.
470x87080000 - 0x870FFFFF: malloc() pool available to SPL.
48
49For the areas that reside within DDR1 they must not be used prior to s_init()
50completing. Note that CONFIG_SYS_TEXT_BASE must be clear of the areas that SPL
51uses while running. This is why we have two versions of the memory map that
52only vary in where the BSS and malloc pool reside.