CODEWITHSUNDEEP
memoryembedded-linuxramu-boot
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Reputation: 2942

How much DRAM does u-boot occupy?

I want to perform some operation(load a small firmware) while i am in u-boot.
Does someone know how much DRAM does u-boot occupy in the beginning and end of DRAM,
so that i can load my firmware in the unoccupied area of DRAM which is not occupied by u-boot?

Upvotes: 2

Views: 6072

Answers (1)

sawdust
sawdust

Reputation: 17077

U-Boot is configurable, so the answer depends on your specific build. The commands and features configured into U-Boot will determine its actual size. Typically U-Boot is built to reside/execute in the upper portion of main memory, and the remainder of low memory is available for whatever.

In your board's config file, the definition for CONFIG_SYS_TEXT_BASE sets the start address of U-Boot. (Older versions of U-Boot had a different method of specifying this start address symbol.)

Examine the generated System.map file (in the same directory as the u-boot.bin executable) for the addresses that the linker has assigned to each entry point.

In your board's config file, there's also something like:

#define CONFIG_SYS_SDRAM_BASE       ATMEL_BASE_CS6
#define CONFIG_SYS_SDRAM_SIZE       0x08000000

to define the physical address range of main memory.

U-Boot will start its stack at the end of SDRAM, or BASE+SIZE. So the region between CONFIG_SYS_TEXT_BASE+(size of u-boot.bin) and the end of SDRAM is the available stack area.

U-Boot will also use memory below CONFIG_SYS_TEXT_BASE for its malloc() pool. The size of that region is defined by CONFIG_SYS_MALLOC_LEN.

So the memory between CONFIG_SYS_SDRAM_BASE and
CONFIG_SYS_TEXT_BASE-CONFIG_SYS_MALLOC_LEN should be available.

ADDENDUM

The above comments apply to a U-Boot that is loaded and executed in main memory (i.e. DRAM).
Some systems execute U-Boot out of ROM or NOR Flash, and then U-Boot will relocate itself to RAM. Some (old?) documentation is here.

Upvotes: 4

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