Datasheet


NOTE
All RTC register reads and writes are done from the processor clock domain clk_sys. All data are synchronised back
and forth between the domains. Writing to the RTC will take 2 clk_rtc clock periods to arrive, additional to the clk_sys
domain. This should be taken into account especially when the reference is slow (e.g. 1 Hz).
4.8.5. Programmer’s Model
There are three setup tasks:
•
Set the 1 sec reference
•
Set the clock
•
Set an alarm
4.8.5.1. Configuring the 1 second reference clock:
Select the source for clk_rtc. This is done outside the RTC registers (see Section 4.8.4).
SDK: https://github.com/raspberrypi/pico-sdk/tree/master/src/rp2_common/hardware_rtc/rtc.c Lines 22 - 40
22 void rtc_init(void) {
23 // Get clk_rtc freq and make sure it is running
24 uint rtc_freq = clock_get_hz(clk_rtc);
25 assert(rtc_freq != 0);
26
27 // Take rtc out of reset now that we know clk_rtc is running
28 reset_block(RESETS_RESET_RTC_BITS);
29 unreset_block_wait(RESETS_RESET_RTC_BITS);
30
31 // Set up the 1 second divider.
32 // If rtc_freq is 400 then clkdiv_m1 should be 399
33 rtc_freq -= 1;
34
35 // Check the freq is not too big to divide
36 assert(rtc_freq <= RTC_CLKDIV_M1_BITS);
37
38 // Write divide value
39 rtc_hw->clkdiv_m1 = rtc_freq;
40 }
4.8.5.2. Setting up the clock
SDK: https://github.com/raspberrypi/pico-sdk/tree/master/src/rp2_common/hardware_rtc/rtc.c Lines 55 - 86
55 bool rtc_set_datetime(datetime_t *t) {
56 if (!valid_datetime(t)) {
57 return false;
58 }
59
60 // Disable RTC
61 rtc_hw->ctrl = 0;
62 // Wait while it is still active
63 while (rtc_running()) {
64 tight_loop_contents();
RP2040 Datasheet
4.8. RTC 571