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| author | Simon Glass <sjg@chromium.org> | 2024-09-26 14:28:51 +0200 |
|---|---|---|
| committer | Tom Rini <trini@konsulko.com> | 2024-10-09 22:04:56 -0600 |
| commit | 77a93ae681646437121b8db85b85dad40016fa51 (patch) | |
| tree | 0235b0914fde35b72d58cc959562cc1697f134c0 /doc | |
| parent | b03b2a45f9f07bdfb0074adf9c8b4339080a7def (diff) | |
| download | u-boot-77a93ae681646437121b8db85b85dad40016fa51.tar.gz | |
doc: Move the generic memory-documentation to doc/
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>
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/develop/index.rst | 1 | ||||
| -rw-r--r-- | doc/develop/memory.rst | 49 |
2 files changed, 50 insertions, 0 deletions
diff --git a/doc/develop/index.rst b/doc/develop/index.rst index 0d0e60ab56c..cbea38d4323 100644 --- a/doc/develop/index.rst +++ b/doc/develop/index.rst @@ -13,6 +13,7 @@ General codingstyle designprinciples docstyle + memory patman process release_cycle diff --git a/doc/develop/memory.rst b/doc/develop/memory.rst new file mode 100644 index 00000000000..e9e65ba4c6c --- /dev/null +++ b/doc/develop/memory.rst @@ -0,0 +1,49 @@ +.. SPDX-License-Identifier: GPL-2.0-or-later + +Memory Management +----------------- + +.. note:: + + This information is outdated and needs to be updated. + +U-Boot runs in system state and uses physical addresses, i.e. the +MMU is not used either for address mapping nor for memory protection. + +The available memory is mapped to fixed addresses using the +memory-controller. In this process, a contiguous block is formed for each +memory type (Flash, SDRAM, SRAM), even when it consists of several +physical-memory banks. + +U-Boot is installed in XIP flash memory, or may be loaded into a lower region of +RAM by a secondary program loader (SPL). After +booting and sizing and initialising DRAM, the code relocates itself +to the upper end of DRAM. Immediately below the U-Boot code some +memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN +configuration setting]. Below that, a structure with global Board-Info +data is placed, followed by the stack (growing downward). + +Additionally, some exception handler code may be copied to the low 8 kB +of DRAM (0x00000000 ... 0x00001fff). + +So a typical memory configuration with 16 MB of DRAM could look like +this:: + + 0x0000 0000 Exception Vector code + : + 0x0000 1fff + 0x0000 2000 Free for Application Use + : + : + + : + : + 0x00fb ff20 Monitor Stack (Growing downward) + 0x00fb ffac Board Info Data and permanent copy of global data + 0x00fc 0000 Malloc Arena + : + 0x00fd ffff + 0x00fe 0000 RAM Copy of Monitor Code + ... eventually: LCD or video framebuffer + ... eventually: pRAM (Protected RAM - unchanged by reset) + 0x00ff ffff [End of RAM] |