[U-Boot-Users] Newbie question
The is not a u-boot question but a question about u-boot source code.
In file cpu/ppc4xx/start.S, the first line for 405GP is: addi r4, r0, 0x0000
I think the purpose of this line is to set r4 as 0x0000, but where is r0 set? Is it supposed to be 0 when the code is started?
Also, why not simply use li r4, 0x0000. Any difference?
Thanks!
Frank
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On Mon, May 10, 2004 at 01:55:32PM -0400, Frank Young wrote:
The is not a u-boot question but a question about u-boot source code.
In file cpu/ppc4xx/start.S, the first line for 405GP is: addi r4, r0, 0x0000
I think the purpose of this line is to set r4 as 0x0000, but where is r0 set? Is it supposed to be 0 when the code is started?
r0 is a special case in a number of PPC assembly instructions. In this case it means that r4 is loaded with the sign extended immediate data. No source register is involved.
Also, why not simply use li r4, 0x0000. Any difference?
No difference at all. In fact there is no li instruction. This is a "simplified mnemonic" that your assembler will translate into an addi instruction.
Ross
participants (2)
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Frank Young -
Ross A. Osborn