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>
diff --git a/doc/develop/memory.rst b/doc/develop/memory.rst
new file mode 100644
index 0000000..e9e65ba
--- /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+ This information is outdated and needs to be updated.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]