why uboot copying itself to RAM

GoogleGroups
1

Hi,

As per my knowledge, MLO(SPL) does basic operation like clock configuration, initialization of external eMMC, ext RAM and copy the u-boot image from eMMC to RAM(DDR3) and jumps to RAM locate where it has copied the u-boot.
But the u-boot startup code seems to mislead me.

Here is the code of u-boot start.S:

#ifndef CONFIG_SKIP_RELOCATE_UBOOT
relocate: /* relocate U-Boot to RAM /
adr r0, _start / r0 ← current position of code /
ldr r1, _TEXT_BASE / test if we run from flash or RAM /
cmp r0, r1 / don’t reloc during debug */
beq stack_setup

ldr r2, _armboot_start
ldr r3, _bss_start
sub r2, r3, r2 /* r2 ← size of armboot /
add r2, r0, r2 / r2 ← source end address */

copy_loop:
ldmia r0!, {r3-r10} /* copy from source address [r0] /
stmia r1!, {r3-r10} / copy to target address [r1] /
cmp r0, r2 / until source end addreee [r2] /
ble copy_loop
#endif / CONFIG_SKIP_RELOCATE_UBOOT */

why is u-boot’s start.S copying itself to ext RAM(DDR3)?

Regards,
Bharath

2

Did you look where the reset vector points?

3

This is a standard procedure for u-boot, why don’t you go ask them…

Regards,

4

Google is working now

https://github.com/LeMaker/u-boot/blob/master/doc/README.ramboot-ppc85xx

5

If you want to avoid it, I believe you could run SPL from internal memory and compile in your kernel boot mechanism.

6

Understood why we need this.

If we are using XIP memory then this is need else, SPL will be doing this operation.

Thanks a lot Jason.

Regards,
Bharath