CC253x: count cpu cycles

Yes, you can use a timer for this. I would recommend to use Timer 1, which has 16 bits. You can also use Timer 3 or Timer 4, but they have only 8 bits, or Timer 2, but that one is typically used for MAC timing in the radio (i.e. if you are using Z-stack or TIMAC).

The exact use depends on the number of cycles you need to count. If it is less than 65536, I'd just do it like this:

unsigned short num_cycles;

T1CTL = 0x00; // Stop Timer 1
T1CNTL = 0x00; // Clear Timer 1
T1CTL = 0x01; // Start Timer 1 in free-running mode; no prescaler
function_to_evaluate(); // Perform operations that you want to time
T1CTL = 0x00; // Stop Timer 1
((unsigned char *)(&num_cycles))[0] = T1CNTL;
((unsigned char *)(&num_cycles))[1] = T1CNTH;
// num_cycles will contain the number of cycles elapsed

If you need to time more than 65535 cycles, you can either use an overflow interrupt of Timer 1 to update an overflow counter or use a prescaler (this will reduce your accuracy).

It is also possible to read out the value of Timer 1 without stopping the timer first if you need to keep the timer running.

geuma geuma said:

I tried to measure the cpu cycles a NOP() does take. The timer1 results an amount of 5 cycles, which could be right because of the context switches and so on. Is this correct?

This looks correct, as it will include the duration of the stop Timer 1 instruction as well as the NOP. The NOP takes 1 cycle, with a potential extra cycle for instruction fetching.

geuma geuma said:

if the timer1 without a prescaler is able to handle 65.535 (because of the 16bit counter) cycles, he would be able to measure (on a 32Mhz MCU with a clock speed of 32.768kHz) nearly 2 seconds, right ??

No, Timer 1 runs on 32 MHz, not 32.768 kHz. So the maximum duration will be 2.048 ms. With a prescaler of 128, you get a maximum of 262 ms, but less accuracy. You can divide further by reducing TICKSPD (cf. Section 4.5 of the CC253x User Guide).

geuma geuma said:

By calculating the time, i forget 1k at the division of the clock speed. Is it true that the timer1 is running with 32.000kHz and the MCU itself is running with 32.768kHz???

No. The maximum CPU clock speed and the maximum Timer 1 tick speed are both 32 MHz (or 32000 kHz - but '.' means decimal point). There is also a 32.768 kHz (or 32768 Hz) crystal oscillator on the CC2530. This is only used for the sleep timer and watchdog timer.

geuma geuma said:

But how do I catch this interrupt request, how do I tell the cc2530 to call a specific function on this?

You can do this in IAR as follows:

volatile unsigned short t1ovf;

#pragma vector=T1_VECTOR
__interrupt void t1_isr(void)
{
  // Clear all Timer 1 source interrupt flags
  T1STAT = 0x00;
  // Increment overflow counter
  t1ovf++;
}

In your main program, you need to enable time Timer 1 overflow interrupt and the global interrupt enable.  You also have some errors in the code and some unnecessary instructions. You could rewrite your program as follows:

unsigned long num_cycles;
T1CTL = 0x00; // stop Timer1
T1CNTL = 0x00; // clear Timer1
//T1CTL |= 0x0C; // setting prescaler to 128

// disable interrupt, clear all interrupt pending flag
T1IE = 0;      // Disable Timer 1 interrupt
T1STAT = 0x00; // Clear all Timer 1 source interrupt flags
T1IF = 0;      // Clear Timer 1 CPU interrupt flag

t1ovf = 0;     // Clear overflow counter

T1IE = 1;      // Enable Timer 1 interrupt
EA = 1;        // Global interrupt enable

T1CTL |= 0x01; // start Timer1 in free-running mode

do_something();
 
T1CTL = 0x00; // stop Timer1
((unsigned char *)(&num_cycles))[0] = T1CNTL; // Set byte 0 of num_cycles
((unsigned char *)(&num_cycles))[1] = T1CNTH; // Set byte 1 of num_cycles
((unsigned short *)(&num_cycles))[1] = t1ovf; // Set byte 2 and 3 of num_cycles

sprintf(line2, "%lu", num_cycles);