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I'm using an ARM Cortex-A8 based processor called as i.MX515. There is linux Ubuntu 9.10 distribution. I'm running a very big application written in C and I'm making use of gettimeofday(); functions to measure the time my application takes. main() { gettimeofday(start); .... .... .... gettimeofday(end); } This method was sufficient to look at what blocks of my application was taking what amount of time. But, now that, I'm trying to optimize my code very throughly, with the gettimeofday() method of calculating time, I see a lot of fluctuation between successive runs (Run before and after my optimizations), so I'm not able to determine the actual execution times, hence the impact of my improvements. Can anyone suggest me what I should do? If by accessing the cycle counter ( Idea suggested on ARM website for Cortex-M3 ) can anyone point me to some code which gives me the steps I have to follow to access the timer registers on Cortex-A8 ? If this method is not very accurate then please suggest some alternatives. Thanks Follow ups Follow up 1: Wrote the following program on Code Sorcery, the executable was generated which when I tried running on the board, I got - Illegal instruction message :( static inline unsigned int get_cyclecount (void) { unsigned int value; // Read CCNT Register asm volatile ("MRC p15, 0, %0, c9, c13, 0\t\n": "=r"(value)); return value; } static inline void init_perfcounters (int32_t do_reset, int32_t enable_divider) { // in general enable all counters (including cycle counter) int32_t value = 1; // peform reset: if (do_reset) { value |= 2; // reset all counters to zero. value |= 4; // reset cycle counter to zero. } if (enable_divider) value |= 8; // enable "by 64" divider for CCNT. value |= 16; //

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