HALDeviceSysPeri_RTC (changes)

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Hardware Abstraction Layer

» HAL Device API

» List of HAL devices

» Real-time clock

(HALDeviceSysPeri_RTC)

Device API

Currently, only API version 0 is defined. API version 0 only supports RTC devices located on the IIC bus.

struct rtcdevice
{
  struct device dev;
  uint8_t timeformat;
  uint8_t formatflags;
  uint8_t padding[2];
  int (*readtime)(struct rtcdevice *rtc,
                  struct rtctime *time);
  int (*writetime)(struct rtcdevice *rtc,
                   const struct rtctime *time);
};

The timeformat and formatflags fields describe the time format that the RTC expects to use when communicating with RISC OS. Currently the only defined timeformat value is 0, indicating BCD.

formatflags is as follows (for BCD):

For situations where bits 2-3 do not equal 10, RISC OS will use the YearLO and YearHI values stored in CMOS to augment the limited data available from the RTC.

Reading and writing the time

The readtime and writetime entry points are used to read from and write to the RTC, respectively. The parameters are as follows:

Upon completion, one of the following return codes must be used:

The rtctime struct which is used to communicate with RISC OS is as follows:

struct rtctime
{
  uint8_t Centiseconds; // BCD centiseconds (00-99)
  uint8_t Seconds; // BCD seconds (00-59)
  uint8_t Minutes; // BCD minutes (00-59)
  uint8_t Hours; // BCD hours (00-23)
  uint8_t DayOfMonth; // BCD day of month (0- or 1- based)
  uint8_t Month; // BCD month (0- or 1- based)
  uint8_t YearLO; // BCD year low value (00-99)
  uint8_t YearHI; // BCD year high value (19-22 due to 5-byte time limits)
};

Note that the writetime routine must be able to cope with 3 different situations:

1. Full time update – all the rtctime members are valid and are expected to be written to the RTC
2. Time update – The DayOfMonth, Month, YearLO and YearHI members will be set to 255. Only the time portion of the RTC should be updated.
3. Date update – The Centiseconds, Seconds, Minutes and Hours members will be set to 255. Only the date portion of the RTC should be updated.

Support in RISC OS

The RTCRTC driver module will use a HAL RTC if the RTC device was registered during the call to HAL_InitDevices, otherwise requests to read or write the RTC will only update the soft copy which is initialised to 02-Jan-1970.

Known implementations

Information sources: Kernel.Hdr.HALDevice, Kernel.Hdr.RTCDevice in CVS