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"Das U-Boot" Source Tree
1.. SPDX-License-Identifier: GPL-2.0-or-later
2
3Memory Management
4-----------------
5
6.. note::
7
8 This information is outdated and needs to be updated.
9
10U-Boot runs in system state and uses physical addresses, i.e. the
11MMU is not used either for address mapping nor for memory protection.
12
13The available memory is mapped to fixed addresses using the
14memory-controller. In this process, a contiguous block is formed for each
15memory type (Flash, SDRAM, SRAM), even when it consists of several
16physical-memory banks.
17
18U-Boot is installed in XIP flash memory, or may be loaded into a lower region of
19RAM by a secondary program loader (SPL). After
20booting and sizing and initialising DRAM, the code relocates itself
21to the upper end of DRAM. Immediately below the U-Boot code some
22memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
23configuration setting]. Below that, a structure with global Board-Info
24data is placed, followed by the stack (growing downward).
25
26Additionally, some exception handler code may be copied to the low 8 kB
27of DRAM (0x00000000 ... 0x00001fff).
28
29So a typical memory configuration with 16 MB of DRAM could look like
30this::
31
32 0x0000 0000 Exception Vector code
33 :
34 0x0000 1fff
35 0x0000 2000 Free for Application Use
36 :
37 :
38
39 :
40 :
41 0x00fb ff20 Monitor Stack (Growing downward)
42 0x00fb ffac Board Info Data and permanent copy of global data
43 0x00fc 0000 Malloc Arena
44 :
45 0x00fd ffff
46 0x00fe 0000 RAM Copy of Monitor Code
47 ... eventually: LCD or video framebuffer
48 ... eventually: pRAM (Protected RAM - unchanged by reset)
49 0x00ff ffff [End of RAM]