ex ELLA / nrf51_rtc

An attempt to provide a Real Time Clock for the nRF51-DK. This code provides rtc.time and rtc.set_time replacements for the similarly named C standard methods (unimplemented for nRF51-DK last I checked). Not very well tested, but it seems to work for simple applications.

Fork of nrf51_rtc by Francis Schumacher

nrf51_rtc.cpp@1:5917157d58c6, 2015-03-02 (annotated)

Committer:
lionello
Date:
Mon Mar 02 08:54:40 2015 +0000
Revision:
1:5917157d58c6
Parent:
0:3677a016109b
Child:
2:e1479e6ffc37
Made update_rtc() an actual static method

Who changed what in which revision?

UserRevisionLine numberNew contents of line
fxschumacher 0:3677a016109b 1 #include "nrf51_rtc.h"
fxschumacher 0:3677a016109b 2
lionello 1:5917157d58c6 3
lionello 1:5917157d58c6 4 nrf51_rtc rtc;
lionello 1:5917157d58c6 5
lionello 1:5917157d58c6 6
fxschumacher 0:3677a016109b 7 int nrf51_rtc::set_time(time_t rawtime) {
fxschumacher 0:3677a016109b 8 // set the current time from a parameter
fxschumacher 0:3677a016109b 9 time_base = rawtime;
fxschumacher 0:3677a016109b 10 rtc_previous = int (NRF_RTC1->COUNTER) / ticks_per_second;
fxschumacher 0:3677a016109b 11 return 0;
fxschumacher 0:3677a016109b 12 }
fxschumacher 0:3677a016109b 13
fxschumacher 0:3677a016109b 14 time_t nrf51_rtc::time() {
fxschumacher 0:3677a016109b 15 // get the current time... and update the underlying variables for tracking time
fxschumacher 0:3677a016109b 16 // ...this routine must be called regularly, before the 24b RTC register can wrap around:
fxschumacher 0:3677a016109b 17 // t < size of register / (LFCLK_FREQUENCY / (NRF_RTC1->PRESCALER + 1))
fxschumacher 0:3677a016109b 18 // size of register = 2^24 ticks
fxschumacher 0:3677a016109b 19 // LFCLK_FREQUENCY = 2^15 cycles/sec
fxschumacher 0:3677a016109b 20 // NRF_RTC1->PRESCALER = 0 -- as (currently) set by mbed library!
fxschumacher 0:3677a016109b 21 // = (2^24)/(2^15/1) = 2^9 seconds = 512 seconds, ~ 8.5 minutes
fxschumacher 0:3677a016109b 22 unsigned int rtc_now = (NRF_RTC1->COUNTER) / ticks_per_second;
fxschumacher 0:3677a016109b 23 unsigned int delta_seconds = ((rtc_now + counter_size_in_seconds) - rtc_previous) % counter_size_in_seconds;
fxschumacher 0:3677a016109b 24 time_base = time_base + (time_t) delta_seconds;
fxschumacher 0:3677a016109b 25 rtc_previous = rtc_now;
fxschumacher 0:3677a016109b 26 return time_base;
fxschumacher 0:3677a016109b 27 }
fxschumacher 0:3677a016109b 28
fxschumacher 0:3677a016109b 29 void nrf51_rtc::update_rtc() {
fxschumacher 0:3677a016109b 30 // for use as interrupt routine, same as "time" but doesn't return a value (as req'd for interrupt)
lionello 1:5917157d58c6 31 rtc.time();
fxschumacher 0:3677a016109b 32 }
fxschumacher 0:3677a016109b 33
fxschumacher 0:3677a016109b 34 nrf51_rtc::nrf51_rtc() {
fxschumacher 0:3677a016109b 35 rtc_previous=0;
fxschumacher 0:3677a016109b 36 time_base=0;
fxschumacher 0:3677a016109b 37 #define LFCLK_FREQUENCY 0x8000
fxschumacher 0:3677a016109b 38 #define RTC_COUNTER_SIZE 0x1000000
fxschumacher 0:3677a016109b 39 ticks_per_second = LFCLK_FREQUENCY / (NRF_RTC1->PRESCALER + 1);
fxschumacher 0:3677a016109b 40 counter_size_in_seconds = RTC_COUNTER_SIZE / ticks_per_second;
fxschumacher 0:3677a016109b 41
fxschumacher 0:3677a016109b 42 // Ticker inside the method doesn't work: the interrupt attachment to the ticker messes up the world (code goes to the weeds)
fxschumacher 0:3677a016109b 43 // ... not needed if "rtc.time()" is called frequently enough (once per 512 seconds)
fxschumacher 0:3677a016109b 44 // ... this scheme (ticker+interrupt routine to update rtc) works correctly when implemented at the next level up
fxschumacher 0:3677a016109b 45 //Ticker rtc_ticker;
fxschumacher 0:3677a016109b 46 //#define RTC_UPDATE 1
fxschumacher 0:3677a016109b 47 //rtc_ticker.attach(this,&nrf51_rtc::update_rtc, RTC_UPDATE); // update the time regularly (must be < duration of 24b timer)
fxschumacher 0:3677a016109b 48 }