So, I'm working with the Atmega128rfa1 board and I'm getting strange results.
My code uses the MAC symbol counter. It uses manual beacon timestamping. In my code the following happens, with PORT_RADIOTIMER_WIDTH being a macro for uint32_t:
....
*((PORT_RADIOTIMER_WIDTH *)(&SCOCR2LL)) = 0;
SCOCR2LL = 0; //set compare registers
*((PORT_RADIOTIMER_WIDTH *)(&SCBTSRLL)) = 0;
SCBTSRLL = 0; //set compare registers
SCCNTHH = SCCNTHL = SCCNTLH = 0;
SCCNTLL = 0; // reset timer value
radiotimer_setPeriod(period); //set period
SCCR0 |= (1 << SCMBTS); // "reset" radiotimer
After this, I immediately try to get the relative time since the timestamp with the following code:
PORT_RADIOTIMER_WIDTH count_time = (uint8_t) SCCNTLL;
count_time |= (uint8_t)SCCNTLH << 8;
count_time |= (uint8_t)SCCNTHL << 16;
count_time |= (uint8_t)SCCNTHH << 24;
PORT_RADIOTIMER_WIDTH beacon_time2;
beacon_time2 = (uint8_t) SCBTSRLL;
beacon_time2 |= (uint8_t)SCBTSRLH << 8;
beacon_time2 |= (uint8_t)SCBTSRHL << 16;
beacon_time2 |= (uint8_t)SCBTSRHH << 24;
PORT_RADIOTIMER_WIDTH beacon_time = (uint16_t)beacon_time2;
PORT_RADIOTIMER_WIDTH captured_time = count_time - beacon_time;
print_debug("radiotimer_getCapturedTime count_time %lu or %u\n", count_time);
print_debug("radiotimer_getCapturedTime beacon_time %lu or %u\n", beacon_time);
print_debug("radiotimer_getCapturedTime captured_time %lu or %u\n",captured_time);
What is printed is:
radiotimer_getCapturedTime count_time 859 or 859
radiotimer_getCapturedTime beacon_time 7090 or 859
radiotimer_getCapturedTime captured_time 4294961065 or 859
Contrary to expectations, the beacon time isn't roughly the same as the count_time, only when comparing as an unsigned int, not as an unsigned long int. What is happening? I'm completely flabbergasted by this.
The print_debug() statements look suspicious. The format calls for two variables, but you only supply one. The 859 printed in each call may be from a variable you are not expecting.
Otherwise, the arithmetic in the ul version is correct. 859 - 7090 does equal 4294961065 in 32-bit unsigned arithmetic.
Try something like:
print_debug("radiotimer_getCapturedTime count_time %lu or %u\n", count_time, count_time);
print_debug("radiotimer_getCapturedTime beacon_time %lu or %u\n", beacon_time, beacon_time);
print_debug("radiotimer_getCapturedTime captured_time %lu or %u\n",captured_time, captured_time);
and see if the results are still always the same in the 16 bit cases.