[ECOS] CYGNUM_HAL_RTC_PERIOD help

[Gary Thomas]

On Tue, 2006-05-09 at 18:22 +0200, Ram Sudhir Tadavarthi wrote:
> Dear all,
> 
> I am a newbie to embedded world and eCos as well. I am trying to bring up
> eCos on Motorola PQ2FADS board. In this journey I have encountered the
> Macros CYGNUM_HAL_RTC_PERIOD which depends on CYGNUM_HAL_RTC_NUMERATOR and
> CYGNUM_HAL_RTC_DENOMINATOR. I have observed that the proper definition of
> these values is required without which the time is calculated incorrectly.
> 
> I tried to experiment with these values to find out the correct one but
> trial and error did not help. I concluded that I won't be successful without
> understanding the underlying concept behind this.
> 
> I have read the following documentation 
> http://ecos.sourceware.org/docs-latest/ref/hal-clocks-and-timers.html
> 
> but still did not understand how to find these values. I only understood
> that the period specifies clock interrupt intervals.
> 
> Can anyone give me a clue/pointer/reference to further documentation to
> proceed further to find out correct CYGNUM_HAL_RTC_NUMERATOR and
> CYGNUM_HAL_RTC_DENOMINATOR values?

The only value you should need to adjust is CYGNUM_HAL_RTC_PERIOD
        cdl_option CYGNUM_HAL_RTC_PERIOD {
            display       "Real-time clock period"
            flavor        data
            default_value { (((CYGHWR_HAL_POWERPC_BOARD_SPEED*1000000)/4)/CYGNUM_HAL_RTC_DENOMINATOR) }
        }

Thus, if you have the value set properly for CYGHWR_HAL_POWERPC_BOARD_SPEED, you
should get the clock running at the right rate.

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------


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