4.33. RTC

4.33.1. Module Files Driver Configuration

none Unit Test

  • tests/unit/app/driver/rtc/test_rtc.c (API, source)

4.33.2. Description

The Real Time Clock (RTC) module uses an NXP PCF2131 IC as RTC. The communication with the IC is made via I2C. A struct RTC_TIME_DATA_s is defined in rtc.h. It holds the RTC data in the format of the IC.

To avoid reading the RTC IC frequently, an RTC system timer is defined in rtc.c with the name rtc_SystemTime. It has the format RTC_SYSTEM_TIMER_EPOCH_s. This struct has two elements:

  • the time in Unix format, which means seconds since January 1st 1970

  • an additional field with milliseconds

The function RTC_IncrementSystemTime() is used to increment the RTC system timer. It must be called every millisecond. It does the following:

  • increment the milliseconds field if its value is under 999

  • otherwise set the millisecond field to 0 and increment the time in Unix format by one second

A getter and a setter function have been defined: RTC_GetSystemTimeRtcFormat() and RTC_SetSystemTimeRtcFormat(). They get or return an element of the type RTC_TIME_DATA_s.

The RTC system timer is set at startup via the function RTC_InitializeSystemTimeWithRtc(). It reads the RTC time from the RTC IC over I2C and uses the value to set the RTC system timer.

To set the RTC Time over CAN, the queue ftsk_rtcSetTimeQueue is used. If a message to set the RTC is received, the data is written in the queue. The function RTC_SetOverCanMessage() reads the queue if it is not empty, and uses the data to set the RTC time of the IC over I2C and then to set the RTC system timer value.

The RTC_Trigger() function is called periodically. It calls RTC_SetOverCanMessage().