F28377S benchmarking, timers seems to be off by a factor of 8, what am I doing wrong

Dear C2000 Champs,

I'm benchmarking some code on the F28375S device and trying to use a timer to measure performance. The results I'm getting seem to be off by a factor of 8. I'm likely doing something wrong but not sure what.

At first, I tried using one of the CPU timers. When those results didn't look right I discovered to the 64-bit free running IPC counter. I tried using that and the results are the same.

I have pasted in my main.c below. To simplify the experiment, I replaced the function I ultimately want to benchmark with a simple series of asm(" NOP") statements. I checked the disassembly and it indeed contains a series of NOPs back to back. I capture a timestamp value just before and just after then the NOPs and then take the delta. In both cases, I end up with what looks like 8 cycles per NOP instruction. This doesn't seem right, I would have expected 1 cycle per NOP. Could it be due to running out of flash or something like that.

I first ran this with 20 NOPs and measured 176 cycles

I next ran it with 40 NOPs and measured 336 cycles

If you take the difference between these two, it should give you the time to run 20 NOPs minus any overhead of reading the timers. 336-176=160 cycles for 20 NOPs which comes out exactly 8 cycles per NOP.

Can anybody explain this?

Thanks

main.c

#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>

#include "InverterControl.h"

#define REG16(addr) *(volatile uint16_t *)(addr)
#define REG32(addr) *(volatile uint32_t *)(addr)
//#define TIMESTAMP()   REG32(0x0C00 + 0x00 /* TIM */);
#define TIMESTAMP()   REG32(0x0005000C /* IPCCOUNTERL */);

int main(void) {

  volatile uint32_t t0, t1, dt;

  // setup CPU timer 0, will be used for timestamping our code
  REG32(0x0C00 + 0x02 /* PRD */) = 0x0FFFFFFF;
  REG32(0x0C00 + 0x00 /* TIM */) = 0x00000000;
  REG32(0x0C00 + 0x04 /* TCR */) = 0x00000000;
    
  //InverterControlInit();

  t0 = TIMESTAMP();
  //InverterRun_ISR();
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  asm(" NOP");
  t1 = TIMESTAMP();

  dt = (t1 - t0);

  printf("dt=%lu\n", dt);

  while (1) {asm(" NOP");}

  return 0;
}