.. comment SPDX-License-Identifier: CC-BY-SA-4.0 .. COMMENT: COPYRIGHT (c) 1988-2002. .. COMMENT: On-Line Applications Research Corporation (OAR). .. COMMENT: All rights reserved. Real-Time Clock Driver ********************** Introduction ============ The Real-Time Clock (*RTC*) driver is responsible for providing an interface to an *RTC* device. The capabilities provided by this driver are: - Set the RTC TOD to RTEMS TOD - Set the RTEMS TOD to the RTC TOD - Get the RTC TOD - Set the RTC TOD to the Specified TOD - Get the Difference Between the RTEMS and RTC TOD .. note:: In this chapter, the abbreviation `TOD` is used for *Time of Day*. The reference implementation for a real-time clock driver can be found in ``c/src/lib/libbsp/shared/tod.c``. This driver is based on the libchip concept and can be easily configured to work with any of the RTC chips supported by the RTC chip drivers in the directory ``c/src/lib/lib/libchip/rtc``. There is a README file in this directory for each supported RTC chip. Each of these README explains how to configure the shared libchip implementation of the RTC driver for that particular RTC chip. The DY-4 DMV177 BSP used the shared libchip implementation of the RTC driver. There were no DMV177 specific configuration routines. A BSP could use configuration routines to dynamically determine what type of real-time clock is on a particular board. This would be useful for a BSP supporting multiple board models. The relevant ports of the DMV177's ``RTC_Table`` configuration table is below: .. code-block:: c #include #include #include bool dmv177_icm7170_probe(int minor); rtc_tbl RTC_Table[] = { { "/dev/rtc0", /* sDeviceName */ RTC_ICM7170, /* deviceType */ &icm7170_fns, /* pDeviceFns */ dmv177_icm7170_probe, /* deviceProbe */ (void *) ICM7170_AT_1_MHZ, /* pDeviceParams */ DMV170_RTC_ADDRESS, /* ulCtrlPort1 */ 0, /* ulDataPort */ icm7170_get_register_8, /* getRegister */ icm7170_set_register_8, /* setRegister */ } }; unsigned long RTC_Count = (sizeof(RTC_Table)/sizeof(rtc_tbl)); rtems_device_minor_number RTC_Minor; bool dmv177_icm7170_probe(int minor) { volatile unsigned16 *card_resource_reg; card_resource_reg = (volatile unsigned16 *) DMV170_CARD_RESORCE_REG; if ( (*card_resource_reg & DMV170_RTC_INST_MASK) == DMV170_RTC_INSTALLED ) return TRUE; return FALSE; } Initialization ============== The ``rtc_initialize`` routine is responsible for initializing the RTC chip so it can be used. The shared libchip implementation of this driver supports multiple RTCs and bases its initialization order on the order the chips are defined in the ``RTC_Table``. Each chip defined in the table may or may not be present on this particular board. It is the responsibility of the ``deviceProbe`` to indicate the presence of a particular RTC chip. The first RTC found to be present is considered the preferred RTC. In the shared libchip based implementation of the driver, the following actions are performed: .. code-block:: c rtems_device_driver rtc_initialize( rtems_device_major_number major, rtems_device_minor_number minor_arg, void *arg ) { for each RTC configured in RTC_Table if the deviceProbe for this RTC indicates it is present set RTC_Minor to this device set RTC_Present to TRUE break out of this loop if RTC_Present is not TRUE return RTEMS_INVALID_NUMBER to indicate that no RTC is present register this minor number as the "/dev/rtc" perform the deviceInitialize routine for the preferred RTC chip for RTCs past this one in the RTC_Table if the deviceProbe for this RTC indicates it is present perform the deviceInitialize routine for this RTC chip register the configured name for this RTC } The ``deviceProbe`` routine returns TRUE if the device configured by this entry in the ``RTC_Table`` is present. This configuration scheme allows one to support multiple versions of the same board with a single BSP. For example, if the first generation of a board had Vendor A's RTC chip and the second generation had Vendor B's RTC chip, RTC_Table could contain information for both. The ``deviceProbe`` configured for Vendor A's RTC chip would need to return TRUE if the board was a first generation one. The ``deviceProbe`` routines are very board dependent and must be provided by the BSP. setRealTimeToRTEMS ================== The ``setRealTimeToRTEMS`` routine sets the current RTEMS TOD to that of the preferred RTC. .. code-block:: c void setRealTimeToRTEMS(void) { if no RTCs are present return invoke the deviceGetTime routine for the preferred RTC set the RTEMS TOD using rtems_clock_set } setRealTimeFromRTEMS ==================== The ``setRealTimeFromRTEMS`` routine sets the preferred RTC TOD to the current RTEMS TOD. .. code-block:: c void setRealTimeFromRTEMS(void) { if no RTCs are present return obtain the RTEMS TOD using rtems_clock_get invoke the deviceSetTime routine for the preferred RTC } getRealTime =========== The ``getRealTime`` returns the preferred RTC TOD to the caller. .. code-block:: c void getRealTime( rtems_time_of_day *tod ) { if no RTCs are present return invoke the deviceGetTime routine for the preferred RTC } setRealTime =========== The ``setRealTime`` routine sets the preferred RTC TOD to the TOD specified by the caller. .. code-block:: c void setRealTime( rtems_time_of_day *tod ) { if no RTCs are present return invoke the deviceSetTime routine for the preferred RTC } checkRealTime ============= The ``checkRealTime`` routine returns the number of seconds difference between the RTC TOD and the current RTEMS TOD. .. code-block:: c int checkRealTime( void ) { if no RTCs are present return -1 obtain the RTEMS TOD using rtems_clock_get get the TOD from the preferred RTC using the deviceGetTime routine convert the RTEMS TOD to seconds convert the RTC TOD to seconds return the RTEMS TOD in seconds - RTC TOD in seconds }