| Tom Rini | acab724 | 2012-02-20 13:27:43 +0000 | [diff] [blame] | 1 | Overview of SPL on OMAP3 devices |
| 2 | ================================ |
| 3 | |
| 4 | Introduction |
| 5 | ------------ |
| 6 | |
| 7 | This document provides an overview of how SPL functions on OMAP3 (and related |
| 8 | such as am35x and am37x) processors. |
| 9 | |
| 10 | Methodology |
| 11 | ----------- |
| 12 | |
| 13 | On these platforms the ROM supports trying a sequence of boot devices. Once |
| 14 | one has been used successfully to load SPL this information is stored in memory |
| 15 | and the location stored in a register. We will read this to determine where to |
| 16 | read U-Boot from in turn. |
| 17 | |
| 18 | Memory Map |
| 19 | ---------- |
| 20 | |
| 21 | This is an example of a typical setup. See top-level README for documentation |
| 22 | of which CONFIG variables control these values. For a given board and the |
| 23 | amount of DRAM available to it different values may need to be used. |
| 24 | Note that the size of the SPL text rodata and data is enforced with a CONFIG |
| 25 | option and growing over that size results in a link error. The SPL stack |
| 26 | starts at the top of SRAM (which is configurable) and grows downward. The |
| 27 | space between the top of SRAM and the enforced upper bound on the size of the |
| 28 | SPL text, data and rodata is considered the safe stack area. Details on |
| 29 | confirming this behavior are shown below. |
| 30 | |
| 31 | A portion of the system memory map looks as follows: |
| 32 | SRAM: 0x40200000 - 0x4020FFFF |
| 33 | DDR1: 0x80000000 - 0xBFFFFFFF |
| 34 | |
| 35 | Option 1 (SPL only): |
| 36 | 0x40200800 - 0x4020BBFF: Area for SPL text, data and rodata |
| Tom Rini | e33b705 | 2012-05-08 07:29:31 +0000 | [diff] [blame] | 37 | 0x4020E000 - 0x4020FFFC: Area for the SPL stack. |
| Tom Rini | acab724 | 2012-02-20 13:27:43 +0000 | [diff] [blame] | 38 | 0x80000000 - 0x8007FFFF: Area for the SPL BSS. |
| 39 | 0x80100000: CONFIG_SYS_TEXT_BASE of U-Boot |
| 40 | 0x80208000 - 0x80307FFF: malloc() pool available to SPL. |
| 41 | |
| 42 | Option 2 (SPL or X-Loader): |
| 43 | 0x40200800 - 0x4020BBFF: Area for SPL text, data and rodata |
| Tom Rini | e33b705 | 2012-05-08 07:29:31 +0000 | [diff] [blame] | 44 | 0x4020E000 - 0x4020FFFC: Area for the SPL stack. |
| Tom Rini | acab724 | 2012-02-20 13:27:43 +0000 | [diff] [blame] | 45 | 0x80008000: CONFIG_SYS_TEXT_BASE of U-Boot |
| 46 | 0x87000000 - 0x8707FFFF: Area for the SPL BSS. |
| 47 | 0x87080000 - 0x870FFFFF: malloc() pool available to SPL. |
| 48 | |
| 49 | For the areas that reside within DDR1 they must not be used prior to s_init() |
| 50 | completing. Note that CONFIG_SYS_TEXT_BASE must be clear of the areas that SPL |
| 51 | uses while running. This is why we have two versions of the memory map that |
| 52 | only vary in where the BSS and malloc pool reside. |