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

20 May 2008

      Hello J.
        Where are you? You promised to have a look.
I can't remove the "disclaimer". Sorry for this.
Regards
Amit Kumar
-----Original Message-----
From: Jean-Christophe PLAGNIOL-VILLARD [mailto:plagnioj@jcrosoft.com]
Sent: Friday, May 16, 2008 2:41 PM
To: Amit Kumar
Cc: u-boot-users@lists.sourceforge.net; Yadvinder Singh Mann
Subject: Re: [U-Boot-Users] PXA255 code in start.S
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
Please do NOT post as HTML
...
Regards
Amit Kumar
Please remove this to
Best Regards,
J.
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