[En-Nut-Discussion] Real time clock on 1.3F not accurate anymore.

[Lars Andersson]

Hi,
it should be 1.3F in the subject line.

I was thinking maybe this is a hardware fault after all?
It is probably not, I have two NUT 1.3F boards with identical behaviour and
flashing the old 3.3.0.1 .HEX file back onto any of the NUTs the problem
is gone. 

Regards,
Lars H. Andersson

> -----Original Message-----
> From: en-nut-discussion-bounces at egnite.de 
> [mailto:en-nut-discussion-bounces at egnite.de] On Behalf Of 
> Lars Andersson
> Sent: Saturday, 18 February, 2006 14:49
> To: 'Ethernut User Chat (English)'
> Subject: [En-Nut-Discussion] Real time clock on 1.3G not 
> accurate anymore.
> 
> 
> Hi group,
> when moving from version 3.3.0.1 to 4.0.1.0 in an application
> running on 1.3F boards I found my homemade RTC using a 1 second
> timer callback was very inaccurate; about 1/60 to slow. I 
> then switched to
> using the
> built-in RTC using stime() and time().
> 
> I find the built-in RTC is also very inaccurate in the same 
> way as the timer
> callback was,
> about one second too slow per minute. 
> 
> I use ethernut 1.3F NUT 4.0.1.0 and winavr 3.4.1 
> NutGetCpuClock() returns 14.7438 MHz
> NutGetTickClock()returns  1024 Hz
> 
> I tried to follow what happens with platform definitions 
> from the configurator and onvards in code generation thinking that
> NUT_TICK_FREQ
> might be wrong. Unfortunately, I got lost in this (for me) very large
> forest.
> It certainly had been easier if the error had been greater 
> like double freq
> or so.
> 
> Any help is appreciated.
> 
> HW manual enhwm16 says:
> - An additional 32.768 kHz crystal (Q2) drives an on-chip asynchronous
> timer,
> - which is typically used for a software realtime clock.
> 
> ostimer.c says:
> Since version 3.9.8, the default frequency had been changed 
> from 16 Hz to 1024 Hz, when the timer is running with an 
> external 32 kHz clock crystal.
> 
> Best regards,
> Lars H. Andersson
> 
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