• Locked Locked
  • Replies 4 replies
  • Subscribers 119 subscribers
  • Views 18335 views
  • Users 0 members are here
Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Concept of Scratch and Preserved Registers

Muhammad Ahsan
Hi,

I am confused in understanding the difference between scratch and preserved registers. I have read the development guide of IAR Embedded Workbench but the topic was written in such a way that I could not get the real sence of it.
Any help or if possible some example that can help me differenciating between the both will be regarded.

Thanks in advance
Parents
  • Note: This was originally posted on 5th April 2011 at http://forums.arm.com

    @ttfn thanks for your detailed reply. Actually what I am unable to understand is that we have two groups of registers r0-r3 and r4-r11. I know that r0-r3 can be used for passing parameters while the remaining cann't. I am passing 4 arguments to the function foo called by main as in your example. Inside function foo I am doing some calculations which involve r0-r6. after return I want to have the same values in all registers as they were before calling foo. Do I need to push r4-r6 on stack before calling foo and then pop them back after return to have the same register values or it will be done automatically as they are called preserved registers. I have seen in the stack window that r0-r3 are pushed to stack, when they are used as parameters.
    I hope you got my point.
Reply
  • Note: This was originally posted on 5th April 2011 at http://forums.arm.com

    @ttfn thanks for your detailed reply. Actually what I am unable to understand is that we have two groups of registers r0-r3 and r4-r11. I know that r0-r3 can be used for passing parameters while the remaining cann't. I am passing 4 arguments to the function foo called by main as in your example. Inside function foo I am doing some calculations which involve r0-r6. after return I want to have the same values in all registers as they were before calling foo. Do I need to push r4-r6 on stack before calling foo and then pop them back after return to have the same register values or it will be done automatically as they are called preserved registers. I have seen in the stack window that r0-r3 are pushed to stack, when they are used as parameters.
    I hope you got my point.
Children
No data