SVC vs SYS mode ?

Ben Baron

Other Parts Discussed in Thread: STARTERWARE-SITARA

In StarterWare the init.S has the following instruction and comment.

@ Enter the start_boot function. The execution still happens in system mode.
@
@Enter_main:
LDR r10,=start_boot
MOV lr,pc @ Dummy return from start_boot
BX r10 @ Branch to start_boot
SUB pc, pc, #0x08 @ looping

This appears to be wrong when code is loaded via the debugger (the saved LR is wrong), but more importantly, my experience with prior ARM7 and ARM9 is that things start out in SVC mode. Any idea why Starterware does this and is it correct?

Thanks!

over 11 years ago

0 Baskaran Chidambaram over 11 years ago

TI__Genius 17370 points

Ben,

I do feel the execution should happen in svc mode. I will try to check on the history and modify if needed.

Thanks for reporting.

Regards

Baskaran

0 Ben Baron over 11 years ago in reply to Baskaran Chidambaram

Prodigy 130 points

Please let the forum know when this issue has been changed in StarterWare so we can pick up the new version.

thanks!

0 Baskaran Chidambaram over 11 years ago in reply to Ben Baron

TI__Genius 17370 points

Ben,

The system mode uses user mode stack and has privileges as SVC mode. So it shouldn't be a problem executing in system mode.

To be consistent with typical svc and user mode, we will change it to svc mode in the next release.

To get automatic intimation of updated package you can register for alert at http://www.ti.com/tool/starterware-sitara

Regards

Baskaran

Processors

Processors forum

SVC vs SYS mode ?