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77a93ae681
Move this section of the README into doc/ with some minor updates to mention SPL and user lower-case hex. Signed-off-by: Simon Glass <sjg@chromium.org> Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
50 lines
1.6 KiB
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50 lines
1.6 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-or-later
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Memory Management
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-----------------
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.. note::
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This information is outdated and needs to be updated.
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U-Boot runs in system state and uses physical addresses, i.e. the
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MMU is not used either for address mapping nor for memory protection.
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The available memory is mapped to fixed addresses using the
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memory-controller. In this process, a contiguous block is formed for each
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memory type (Flash, SDRAM, SRAM), even when it consists of several
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physical-memory banks.
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U-Boot is installed in XIP flash memory, or may be loaded into a lower region of
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RAM by a secondary program loader (SPL). After
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booting and sizing and initialising DRAM, the code relocates itself
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to the upper end of DRAM. Immediately below the U-Boot code some
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memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
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configuration setting]. Below that, a structure with global Board-Info
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data is placed, followed by the stack (growing downward).
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Additionally, some exception handler code may be copied to the low 8 kB
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of DRAM (0x00000000 ... 0x00001fff).
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So a typical memory configuration with 16 MB of DRAM could look like
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this::
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0x0000 0000 Exception Vector code
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:
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0x0000 1fff
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0x0000 2000 Free for Application Use
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:
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:
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:
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:
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0x00fb ff20 Monitor Stack (Growing downward)
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0x00fb ffac Board Info Data and permanent copy of global data
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0x00fc 0000 Malloc Arena
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:
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0x00fd ffff
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0x00fe 0000 RAM Copy of Monitor Code
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... eventually: LCD or video framebuffer
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... eventually: pRAM (Protected RAM - unchanged by reset)
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0x00ff ffff [End of RAM]
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