Computer Systems Experiments 22 | Timer Module

Series: Computer Systems Experiments

Computer Systems Experiments 22 | Timer Module

To start with this experiment, we have to use the code that we have pulled from the clock-starter repo. The direction of this experiment is,

~/ComputerSysE/environment/include/timer.h

And we need to complete the timer_get_ticks function in the file src/lib/timer.c . The other functions timer_delay_us, timer_delay_ms, and timer_delay is already given by the starter code. For this module, note that we only care about the lower 32-bits of the system timer. And this system timer is an onboard read-only peripheral that is initialized to zero when the Pi powers up and is continuously incremented once every microsecond behind the scenes.

To set the address of this lower 32-bits register,

static volatile unsigned int *TIME  =  (unsigned int *) 0x20003004;

Then to return the time counted, we can use,

unsigned int timer_get_ticks(void) {
    return *TIME;
}

Then we uncomment the test_timer(); in the file test_gpio_timer.c . And run,

$ make test

to test this time.c script. If the green light is shining, congratulations!