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diff --git a/doc/SPL/README.omap3 b/doc/SPL/README.omap3 new file mode 100644 index 0000000..cc5d5c0 --- /dev/null +++ b/doc/SPL/README.omap3 @@ -0,0 +1,74 @@ +Overview of SPL on OMAP3 devices +================================ + +Introduction +------------ + +This document provides an overview of how SPL functions on OMAP3 (and related +such as am35x and am37x) processors. + +Methodology +----------- + +On these platforms the ROM supports trying a sequence of boot devices. Once +one has been used successfully to load SPL this information is stored in memory +and the location stored in a register. We will read this to determine where to +read U-Boot from in turn. + +Memory Map +---------- + +This is an example of a typical setup. See top-level README for documentation +of which CONFIG variables control these values. For a given board and the +amount of DRAM available to it different values may need to be used. +Note that the size of the SPL text rodata and data is enforced with a CONFIG +option and growing over that size results in a link error. The SPL stack +starts at the top of SRAM (which is configurable) and grows downward. The +space between the top of SRAM and the enforced upper bound on the size of the +SPL text, data and rodata is considered the safe stack area. Details on +confirming this behavior are shown below. + +A portion of the system memory map looks as follows: +SRAM: 0x40200000 - 0x4020FFFF +DDR1: 0x80000000 - 0xBFFFFFFF + +Option 1 (SPL only): +0x40200800 - 0x4020BBFF: Area for SPL text, data and rodata +0x4020BC00 - 0x4020FFFC: Area for the SPL stack. +0x80000000 - 0x8007FFFF: Area for the SPL BSS. +0x80100000: CONFIG_SYS_TEXT_BASE of U-Boot +0x80208000 - 0x80307FFF: malloc() pool available to SPL. + +Option 2 (SPL or X-Loader): +0x40200800 - 0x4020BBFF: Area for SPL text, data and rodata +0x4020BC00 - 0x4020FFFC: Area for the SPL stack. +0x80008000: CONFIG_SYS_TEXT_BASE of U-Boot +0x87000000 - 0x8707FFFF: Area for the SPL BSS. +0x87080000 - 0x870FFFFF: malloc() pool available to SPL. + +For the areas that reside within DDR1 they must not be used prior to s_init() +completing. Note that CONFIG_SYS_TEXT_BASE must be clear of the areas that SPL +uses while running. This is why we have two versions of the memory map that +only vary in where the BSS and malloc pool reside. + +Estimating stack usage +---------------------- + +With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate +stack usage at various points in run sequence of SPL. The -fstack-usage option +to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that +will give stack usage information and cflow can construct program flow. + +Must have gcc 4.6 or later, which supports -fstack-usage + +1) Build normally +2) Perform the following shell command to generate a list of C files used in +SPL: +$ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list +3) Execute cflow: +$ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER + +cflow will spit out a number of warnings as it does not parse +the config files and picks functions based on #ifdef. Parsing the '.i' +files instead introduces another set of headaches. These warnings are +not usually important to understanding the flow, however. |