This is the mail archive of the ecos-discuss@sources.redhat.com mailing list for the eCos project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

RE: PowerPC decrementer and Real Time Clock questions


Thanks Gary

	This clears it up somewhat and explains some of the things I have been seeing, but what still confuses me is
	in setting the real time clock, and interrupt vector is attached for the RTC(the internal device) and if the 	decrementer is being used I thought it had its own exception trap.  And the hardware real time clock is a external
	interrupt at level 0...


	Thanks for the time, I think I am getting close to RTC enlightenment here..

Roman


-----Original Message-----
From: Gary Thomas [mailto:gary@mlbassoc.com] 
Sent: Thursday, July 15, 2004 5:30 PM
To: Rycerz Roman-G11565
Cc: Ecos-Discuss@Sources. Com (ecos-discuss@sources.redhat.com)
Subject: Re: [ECOS] 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

-- 
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]