[U-Boot-Users] PXA255 code in start.S

[Jean-Christophe PLAGNIOL-VILLARD]

On 12:14 Fri 16 May     , Amit Kumar wrote:
>     
> 
>    Hello,
> 
>                Kindly refer code at path     UBOOT / u-boot / cpu / pxa /
>    start.S
> 
>     
> 
>    Code:
> 
>                .macro      irq_save_user_regs
> 
>          sub   sp, sp, #S_FRAME_SIZE
> 
>          stmia sp, {r0 - r12}                /* Calling r0-r12      */
> 
>          add   r8, sp, #S_PC
> 
>          stmdb r8, {sp, lr}^                 /* Calling SP, LR      */
> 
>          str   lr, [r8, #0]                  /* Save calling PC           */
> 
>          mrs   r6, spsr
> 
>          str   r6, [r8, #4]                  /* Save CPSR                 */
> 
>          str   r0, [r8, #8]                  /* Save OLD_R0               */
> 
>          mov   r0, sp
> 
>          .endm
> 
>     
> 
>    Why there is need to save R0? If we refer ARM architecture (section what
>    all happens when interrupt comes) there is no need to save R0.
> 
>     
> 
>    Moreover, there is no need of writing such big piece of code it can be
>    replaced with below given four liner code:
> 
>     
> 
>          Sub   lr, lr, #4
> 
>                Stmfd    sp! , {r0-r12, lr}
> 
>                MRS     r1, spsr
> 
>                Stmfd    sp! , {r1}
> 
>     
> 
>    Similarly we can write small code for restore of stack
> 
>                 .macro     irq_restore_user_regs
> 
>                             Ldmfd  sp! , {r1}
> 
>                            MSR         cpsr_c ,  R1
>                            ldmfd    sp!,  {r0-r12, pc}^
> 
>                 .endm
> 
>     
> 
>    Can anybody clarify?
I'll take a look, I'm currently cleaning the board init

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> 
>     
> 
>    Regards
> 
>    Amit Kumar
> 
>     
> 
>     
> 
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Please remove this to

Best Regards,
J.