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Example of instructions, doesn't use functional unit at all?

Hello to all,

I need a small help with the processor instructions. Can anybody provide me an example where during execution, the functional unit must not be used or it must be deactivated? 

All data-processing and data-transfer instruction need the functional unit. Initially, I thought the NOP instruction can be one of the examples, but while going through the documentations, I got to know that NOP instruction is nothing but the MOV R8,R8. 

I really want to measure the effect of functional unit activation and deactivation. So, is there any instruction example or any measurement technique, which will be helpful in our case?

I am working on ARM Cortex-M4.

Thanking you in advance,

Warm Regards,

Himanshu

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  • >I got to know that NOP instruction is nothing but the MOV R8,R8.

    That's not true for Cortex-M (and recent Arm processors). Before ARM1176 it is correct that there is no real "NOP" instruction and development tools use MOV instruction to implement NOP. But since ARM1176 we have added NOP instruction (as part of Thumb-2 technology) and all Cortex-M processors support NOP instruction.

    regards,

    Joseph

Reply
  • >I got to know that NOP instruction is nothing but the MOV R8,R8.

    That's not true for Cortex-M (and recent Arm processors). Before ARM1176 it is correct that there is no real "NOP" instruction and development tools use MOV instruction to implement NOP. But since ARM1176 we have added NOP instruction (as part of Thumb-2 technology) and all Cortex-M processors support NOP instruction.

    regards,

    Joseph

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