Datasheet

51 } while (true);
52 return ((uint64_t) hi << 32u) | lo;
53 }
4.6.4.2. Set an alarm
The standalone timer example, timer_lowlevel, demonstrates how to set an alarm at a hardware level, without the
additional abstraction over the timer that the SDK provides. To use these abstractions see Section 4.6.4.4.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/timer/timer_lowlevel/timer_lowlevel.c Lines 25 - 72
25 // Use alarm 0
26 #define ALARM_NUM 0
27 #define ALARM_IRQ TIMER_IRQ_0
28
29 // Alarm interrupt handler
30 static volatile bool alarm_fired;
31
32 static void alarm_irq(void) {
33 // Clear the alarm irq
34 hw_clear_bits(&timer_hw->intr, 1u << ALARM_NUM);
35
36 // Assume alarm 0 has fired
37 printf("Alarm IRQ fired\n");
38 alarm_fired = true;
39 }
40
41 static void alarm_in_us(uint32_t delay_us) {
42 // Enable the interrupt for our alarm (the timer outputs 4 alarm irqs)
43 hw_set_bits(&timer_hw->inte, 1u << ALARM_NUM);
44 // Set irq handler for alarm irq
45 irq_set_exclusive_handler(ALARM_IRQ, alarm_irq);
46 // Enable the alarm irq
47 irq_set_enabled(ALARM_IRQ, true);
48 // Enable interrupt in block and at processor
49
50 // Alarm is only 32 bits so if trying to delay more
51 // than that need to be careful and keep track of the upper
52 // bits
53 uint64_t target = timer_hw->timerawl + delay_us;
54
55 // Write the lower 32 bits of the target time to the alarm which
56 // will arm it
57 timer_hw->alarm[ALARM_NUM] = (uint32_t) target;
58 }
59
60 int main() {
61 stdio_init_all();
62 printf("Timer lowlevel!\n");
63
64 // Set alarm every 2 seconds
65 while (1) {
66 alarm_fired = false;
67 alarm_in_us(1000000 * 2);
68 // Wait for alarm to fire
69 while (!alarm_fired);
70 }
71 }
RP2040 Datasheet
4.6. Timer 558