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Re: PowerPC decrementer and Real Time Clock questions


On Thu, 2004-07-15 at 16:13, Rycerz Roman-G11565 wrote:
> Hi
> 
> I am hoping someone can help me, I am very confused on how the 
> Decrementer and the Real Time Clock are used.  I have got Redboot 
> running on a MPC5554 which uses the decrementer to create delays. 
> This is good and ok in my mind.  Where the confusion comes in is when 
> the Kernel creates the real time clock.  On the MPC555 processor the 
> role of the decrementer and the RTC have me very confused.    To add 
> to the confusion, the decrementer can generate a exception while the 
> rtc share an interrupt with the rest of the system.   
> 
> Does anyone know how these are all interrelated ???, is there a simpler
> PPC implementation that would be a good model ???
> 
> While both the MPC555 & MPC5554 have a decrementer, periodic timer 
> and a watchdog, the MPC5554 does not have a RTC.
> 
> Any enlightenment here for a ecos porting newbie ????

These are not related at all.  eCos uses the decrementer to implement
an internal device known as the real time clock.  This "device" has
nothing to do with any hardware RTC.  We use it to keep track of time
and events, but do not rely on hardware to support these concepts.

It is possible to use a hardware RTC to tell eCos about the time of
day (without it, time starts at 0 and the date is more or less 
undefined).  Look at the TAMS MOAB (a PPC405 board) to see how this 
might be done.

-- 
Gary Thomas <gary@mlbassoc.com>
MLB Associates


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