RTEMS 4.7.2 On-Line Library

Real-Time Clock Driver Initialization

BSP and Device Driver Development Guide

11.2: 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:

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.

BSP and Device Driver Development Guide