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Question about Program counter

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]

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Peter Harris over 12 years ago

Note: This was originally posted on 3rd October 2012 at http://forums.arm.com

For ARM ISA you can also put operand 2 though the shifter "for free" as part of the instruction, so if you want to do x = 2y - z you can do rsb x, z, y,#LSL1

EDIT: Correct shift - too late for this
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Peter Harris over 12 years ago

Note: This was originally posted on 3rd October 2012 at http://forums.arm.com

For ARM ISA you can also put operand 2 though the shifter "for free" as part of the instruction, so if you want to do x = 2y - z you can do rsb x, z, y,#LSL1

EDIT: Correct shift - too late for this
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