problems with MPC8xx internal RTC !?

problems with MPC8xx internal RTC !?

[Steven Scholz]

Hi there,

I am using an MPC855T, external clocked with 16 MHz. Using the internal PLLs it
runs at 80MHz/40Mhz. An 32.768KHZ crystal is connected to clock the MPCs
internal RTC. A battery is there as well.

All seems to be fine. But I realized that the RTC runs too fast. It seems to be
releated to systems restarts.

It tested. After 25 reboots the RTC is already SIX seconds ahead!!!

rdate:   Wed Jan 29 10:03:58 2003
date:    Wed Jan 29 10:04:04 CET 2003
hwclock: Wed Jan 29 10:04:04 2003  0.000000 seconds

Any ideas?

Thanks,

Steven


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Re: problems with MPC8xx internal RTC !?

[Frank Robbins]

Just an a side note  has the errata for the RTC been fixed on the MPC855T it
is not fixed on the 860T  and I believe this feature is now missing on
future MPC 866T, 857 variants.

If not it will draw several mA from your battery and discharge it very
quickly

Frank

----- Original Message -----
From: "Steven Scholz" <steven.scholz@imc-berlin.de>
To: "Linuxppc-Embedded" <linuxppc-embedded@lists.linuxppc.org>
Sent: Wednesday, January 29, 2003 9:05 AM
Subject: problems with MPC8xx internal RTC !?


>
> Hi there,
>
> I am using an MPC855T, external clocked with 16 MHz. Using the internal
PLLs it
> runs at 80MHz/40Mhz. An 32.768KHZ crystal is connected to clock the MPCs
> internal RTC. A battery is there as well.
>
> All seems to be fine. But I realized that the RTC runs too fast. It seems
to be
> releated to systems restarts.
>
> It tested. After 25 reboots the RTC is already SIX seconds ahead!!!
>
> rdate:   Wed Jan 29 10:03:58 2003
> date:    Wed Jan 29 10:04:04 CET 2003
> hwclock: Wed Jan 29 10:04:04 2003  0.000000 seconds
>
> Any ideas?
>
> Thanks,
>
> Steven
>
>
>


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RE: problems with MPC8xx internal RTC !?

[Allen Curtis]

> Just an a side note  has the errata for the RTC been fixed on the
> MPC855T it
> is not fixed on the 860T  and I believe this feature is now missing on
> future MPC 866T, 857 variants.

Do you have a patch you would like to contribute?

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Re: problems with MPC8xx internal RTC !?

[Frank Robbins]

There is no patch .. If we could patch the hardware we would all be happy!

The chip is ill  there was a Mask error when it was originally made. It has
never been fixed on the 860T , and on most of the 855T silicon this was also
the case.. though it was down for a fix on of the errata sheets whether this
has been done I am unsure check www.mot-sps.com

The fix is to use a RTC clock chip and not use the VKAPWR just connect it to
3V3 (Don't leave it disconnected otherwise you will be able fry eggs on the
chip.. it gets hot when left unconnected). Change your hardware to use a RTC
chip or live with the power drain.

Frank

----- Original Message -----
From: "Allen Curtis" <acurtis@onz.com>
To: "Frank Robbins" <Frank.Robbins@Analogue-Micro.com>; "Steven Scholz"
<steven.scholz@imc-berlin.de>
Cc: <linuxppc-embedded@lists.linuxppc.org>
Sent: Wednesday, January 29, 2003 2:53 PM
Subject: RE: problems with MPC8xx internal RTC !?


> > Just an a side note  has the errata for the RTC been fixed on the
> > MPC855T it
> > is not fixed on the 860T  and I believe this feature is now missing on
> > future MPC 866T, 857 variants.
>
> Do you have a patch you would like to contribute?


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