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.
Dependents: nRF51_rtc_example LoRa_PIR BLE_Lightning_sensor BLE_AlarmWatch ... more
Diff: nrf51_rtc.cpp
- Revision:
- 0:3677a016109b
diff -r 000000000000 -r 3677a016109b nrf51_rtc.cpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/nrf51_rtc.cpp Sun Feb 08 01:28:47 2015 +0000 @@ -0,0 +1,46 @@ +#include "nrf51_rtc.h" + +int nrf51_rtc::set_time(time_t rawtime) { + // set the current time from a parameter + time_base = rawtime; + rtc_previous = int (NRF_RTC1->COUNTER) / ticks_per_second; + return 0; +} + +time_t nrf51_rtc::time() { + // get the current time... and update the underlying variables for tracking time + // ...this routine must be called regularly, before the 24b RTC register can wrap around: + // t < size of register / (LFCLK_FREQUENCY / (NRF_RTC1->PRESCALER + 1)) + // size of register = 2^24 ticks + // LFCLK_FREQUENCY = 2^15 cycles/sec + // NRF_RTC1->PRESCALER = 0 -- as (currently) set by mbed library! + // = (2^24)/(2^15/1) = 2^9 seconds = 512 seconds, ~ 8.5 minutes + unsigned int rtc_now = (NRF_RTC1->COUNTER) / ticks_per_second; + unsigned int delta_seconds = ((rtc_now + counter_size_in_seconds) - rtc_previous) % counter_size_in_seconds; + time_base = time_base + (time_t) delta_seconds; + rtc_previous = rtc_now; + return time_base; +} + +void nrf51_rtc::update_rtc() { + // for use as interrupt routine, same as "time" but doesn't return a value (as req'd for interrupt) + // ...but this is useless since the compiler seems to be unable to correctly attach a member function to the ticker interrupt + // ...the exact same interrupt routine attached to a ticker works fine when declared outside the method + nrf51_rtc::time(); +} + +nrf51_rtc::nrf51_rtc() { + rtc_previous=0; + time_base=0; + #define LFCLK_FREQUENCY 0x8000 + #define RTC_COUNTER_SIZE 0x1000000 + ticks_per_second = LFCLK_FREQUENCY / (NRF_RTC1->PRESCALER + 1); + counter_size_in_seconds = RTC_COUNTER_SIZE / ticks_per_second; + + // Ticker inside the method doesn't work: the interrupt attachment to the ticker messes up the world (code goes to the weeds) + // ... not needed if "rtc.time()" is called frequently enough (once per 512 seconds) + // ... this scheme (ticker+interrupt routine to update rtc) works correctly when implemented at the next level up + //Ticker rtc_ticker; + //#define RTC_UPDATE 1 + //rtc_ticker.attach(this,&nrf51_rtc::update_rtc, RTC_UPDATE); // update the time regularly (must be < duration of 24b timer) +}