Posted on May 17, 2011 at 13:16The easiest way to do this is to use the SysTick timer, which doesn't require much to setup and doesn't have to be cascaded while still giving a good range. You can use either clock ticks or clock ticks / 8 to measure the period. You don't have to use interrupts - you only have to read the counter before and after and take the difference, with some care taken to handle the case where the counter overflowed.
Try this:
Code:
int32_t clock_ticks;
// Enable SysTick with (AHB / 8) clock, use 0x5 for AHB
STK_CTRL = 0x1;
clock_ticks = STK_VAL;
// Perform your operation here
clock_ticks = (STK_VAL - clock_ticks) & 0xFFFFFF;
// Do something to report clock_ticks, ie look at the value in a
// debugger, print it over USART, etc
You can find the addresses of STK_CTRL and STK_VAL in the STM32 programming manual (document PM0056).
The & 0xFFFFFF should take care of overflow. The number can be interpreted as (1 / clock_speed) * 8 * clock_ticks seconds. So if your clock speed is 72MHz and clock_ticks is 1000 then it means your operation took (1 / 72000000) * 8 * 1000 = 1.11111e-4 seconds, or about 111 microseconds. If you use STK_CTRL = 0x5 then take out the * 8 in the calculations.
