[ECOS] Re: RE : [ECOS] Understanding CYGNUM_HAL_RTC_PERIOD NUMERATOR DENOMINATOR

[David Fernandez <dfernandez at cct dot co dot uk>]

On Wed, 2006-06-21 at 09:19 +0200, FALL wrote:
> Good Day, I have successfully compiled and ran ecos on an oki platform.
> I am however not understanding how to setup the NUMERATOR DENOMINATOR
> RTC_PERIOD per my platform specs. I have read the documentation but I am
> still not clear on what values I should use.  Specifically, my processor
> is runningat 33Mhz, when the hal_clock_initialize is called, what is the
> relationship between that and the above mentioned values.
> 
> Moussa
> hi Moussa try this config:
> cdl_component CYGNUM_HAL_CPUCLOCK {
>         display       "cpu clock"
          display       "cpu clock (Mhz.)"
>         flavor        data
>         calculated 33000000
> 	no_define
> 	define -file system.h CYGNUM_HAL_CPUCLOCK
>         description   "Frequency of cpu clock in Hz."
>     }
> ....
> # Real-time clock/counter specifics
>     cdl_component CYGNUM_HAL_RTC_CONSTANTS {
>         display       "Real-time clock constants"
>         flavor        none
> 
>         cdl_option CYGNUM_HAL_RTC_NUMERATOR {
>             display       "Real-time clock numerator"
              display       "Real-time clock numerator (nanoseconds per second)"
>             flavor        data
>             default_value 1000000000
>         }
>         cdl_option CYGNUM_HAL_RTC_DENOMINATOR {
>             display       "Real-time clock denominator"
              display       "Real-time clock denominator (wraps per second)"
>             flavor        data
>             default_value 100
>         }
>         cdl_option CYGNUM_HAL_RTC_PERIOD {
>             display       "Real-time clock period"
              display       "Real-time clock period (ticks per wrap)"
>             flavor        data
>             default_value (CYGNUM_HAL_CPUCLOCK/CYGNUM_HAL_RTC_DENOMINATOR) -1
>         }
>     }

The way I see that in my intel platform is as modified above.

The DENOMINATOR allows you to calculate ticks and specifies the OS timer
"tick" (usually 10 milliseconds)

The NUMERATOR allows you to convert periods into frequencies and
viceversa (periods in nanoseconds to/from frequencies in Mhz.)

The only reason you want to change DENOMINATOR is to get a different
time granularity in the OS.

The only reason you want to change the NUMERATOR is if you need to use
different units of periods or frequencies becuase may be that the
calculi you need to do exceeds the numerical capacity of your scalar
types.

David.

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