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Question about Program counter

Camp Phor
Note: This was originally posted on 1st October 2012 at http://forums.arm.com

[size=2]Hey[/size]

[size=2]Can someone please explain why instructions that modify the value of the PC (such as branches or [/size][size=2]mov pc, lr[/size][size=2]) requireadditional clock cycles to execute than those who don't operate on the PC. [/size]

[size=2]does branch link modify the value of PC or LR?[/size]

[size=2]
[/size]

[size=2]thanks [/size]

Parents
  • Note: This was originally posted on 2nd October 2012 at http://forums.arm.com

    [size=2]awesome, thanks heaps.[/size]
    [size=2] [/size]
    [size=2]I've actually got heaps of questions i would like to ask...haha[/size]

    [size=2][size=2][size=2]What does the [/size][size=2]rsb [/size][size=2]instruction do?  we'll i know what it does but don't fully understand why we would use rsb rather than sub...?[/size][/size][/size]
    [size=2][size=2][size=2] [/size][/size][/size]
    [size=2][size=2][size=2]could someone give an example of an expression that would require the use of rsb rather than sub?[/size][/size][/size]
    [size=2][size=2][size=2] [/size][/size][/size]
    [size=2][size=2][size=2]thanks heaps~[/size][/size][/size]
Reply
  • Note: This was originally posted on 2nd October 2012 at http://forums.arm.com

    [size=2]awesome, thanks heaps.[/size]
    [size=2] [/size]
    [size=2]I've actually got heaps of questions i would like to ask...haha[/size]

    [size=2][size=2][size=2]What does the [/size][size=2]rsb [/size][size=2]instruction do?  we'll i know what it does but don't fully understand why we would use rsb rather than sub...?[/size][/size][/size]
    [size=2][size=2][size=2] [/size][/size][/size]
    [size=2][size=2][size=2]could someone give an example of an expression that would require the use of rsb rather than sub?[/size][/size][/size]
    [size=2][size=2][size=2] [/size][/size][/size]
    [size=2][size=2][size=2]thanks heaps~[/size][/size][/size]
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