CODEWITHSUNDEEP
armbootbootloader
Alex
Alex

Reputation: 28

How ARM CPU loading bootloader?

As I know, CPU can access RAM directly. Device RAM is empty on start and CPU don't know from where to load bootloader into the RAM for executing it. Even it can do nothing because call stack should be empty too as I think. Yet how is bootloader program copied into the RAM for further execution?

This should happening with embedded devices such as smartphones. On a x86 PCs BIOS is responsible for loading MBR section from disk to RAM as I know.

Upvotes: 0

Views: 2444

Answers (2)

Clifford
Clifford

Reputation: 93556

A bootloader in RAM is a secondary bootloader; invariably there is code in a ROM of some kind containing a primary bootstrap that loads the secondary bootstrap. Often that ROM is mask-ROM on the chip it self.

Typically on an ARM application processor such as a Cortex-A the primary bootstrap will load code to RAM from NAND flash or SD card. ARM Cortex-M often run code directly from ROM in any case.

Upvotes: 1

old_timer
old_timer

Reputation: 71586

you have the same problem with an x86. and the same solution in general (as with any other processor as well), you put a rom/flash in the address space where the processor boots and/or where its vector table is.

there are some other solutions like having other logic that reads from some non volatile storage and places it in the boot/vector space, or other logic that provides an interface for some other processor/computer to download into the board/chip and then release reset.

Upvotes: 0

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