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