Synching clock manager

[Joel Sherrill]

Arun Govind wrote:
> 
> thank you for your response.
> I wonder what should you have meant by a *separate* hardware clock. I'm using a my PC itself as the target and all I wanted to synch the time with the BIOS time. I used the rtems_clock_set using a hard coded time and that worked. But how can I get the current time from BIOS? Sorry, I don't know much about BIOS routines.. Is there any prebuilt function that will do that?

In general terms, time is managed by two types of devices.  

  + interval/countdown timer
  + real-time clock

The interval/countdown timer device gives periodic interrupts.
As part of serving that interrupt, the rtems_clock_tick service
is called which results in "wall time" being moved ahead one
tick.  It doesn't matter what the time of day is -- it moves
ahead a tick.  This is the basis for all wall time and timeout
servicing in RTEMS.

The real-time clock is the hardware device responsible for 
letting the system know the real wall time.  It is often only
capable of reporting time to the second resolution.  This device
is battery backed so wall time is maintained when power is off.
RTC devices often include some small amount of some type of 
non-volatile memory.  This is often used for configuration type
information.  Many embedded devices do NOT have this type of device.

The pc386 BSP you are using has routines to read the RTC hardware.
See pc386/clock/rtc.c but call rtc_read() to get the TOD from the 
HW RTC.  Then call rtems_clock_set() to set RTEMS view of the
TOD.

--joel

> Arun
> --
> 
> On Tue, 17 Dec 2002 17:01:53
>  Ian Caddy wrote:
> >Hi Arun,
> >
> >Yes, if you have a seperate hardware clock, you will need to get its
> >time on startup and then perform:
> >
> >    /* Now we set our system time */
> >    status = rtems_clock_set(&tRTEMSTime);
> >
> >This can be performed in your init task when your system starts up.
> >
> >regards,
> >
> >Ian Caddy
> >
> >
> >Arun Govind wrote:
> >> Do I need to call some special routines to synch the rtems clock manager with the hardware clock? I've #defined CONFIGURE_TEST_NEEDS_CLOCK_DRIVER    in my test. But any calls to get the current time returns me some time around midnight, January 1st 1988.
> >> thanks for any help
> >> Arun
> >>
> >>
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