C2000 Assembler Repeated "NOP" instructions

warren hill

Looking at some example code from TI I can see multiple repeated NOP instructions as shown below

I am using a Piccolo A processor

---start example---

        MOV       @_EPwm4Regs.AQCTLB, #0x0115
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       NOP
       MOVW    DP,#_EPwm2Regs.TZCTL

---end example--

I note that the "NOP" instruction can be used with "RPT". Is the does the following code take the same time to execute and does the answer change depending on if this code is in Flash or RAM? It clearly takes up less space and requires the processor to fetch less instructions does that mean the following code will run faster?

If I have counted correctly there were 18 NOP instructions above

---start example---

        MOV       @_EPwm4Regs.AQCTLB, #0x0115
        RPT        #17
||    NOP        MOVW    DP,#_EPwm2Regs.TZCTL

---end example--

Thanks In advance

Warren

over 13 years ago

0 Mark Swanson over 13 years ago

TI__Expert 3520 points

Warren,

The two code examples should take the same number of CPU cycles to execute due to the C28x instruction pipeline described in the TMS320C28x CPU and Instruction Set Reference Guide. Execution time will be shorter running from RAM due to wait states being needed to run from Flash. Further discussion and documentation on this subject can be found here: http://processors.wiki.ti.com/index.php?title=C2000_Flash_Common_Issues/FAQs#Code_Runs_Slower_in_Flash_than_RAM. The code itself will not run 'faster' in the sense of fewer CPU cycles, which is the way I interpret your final question. Ignoring the effects of Flash and RAM the two examples should run identically except for the benefit of smaller code size seen in the second example as you already mentioned.

Best Regards,

Mark-

0 Mitja Nemec over 13 years ago in reply to Mark Swanson

Genius 5885 points

Waren, Mark

One difference though is that code with RPT is non-interruptible. So if you have any interrupts that have to have fast response time an low jitter requirement, the long version is a way to go

Regards, Mitja

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C2000 Assembler Repeated "NOP" instructions