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RE: [avr-gcc-list] Re: ATmega168 FreeRTOS code

From: Vedantam Prasanth-AVP035
Subject: RE: [avr-gcc-list] Re: ATmega168 FreeRTOS code
Date: Thu, 6 Apr 2006 18:42:18 +0800


We have been facing a random problem where data sent to the ATMega128 on one of 
the UARTs (UART1 multiplexed on ports PD2 and PD3) gets corrupted. We have 
verified that the data being transmitted on the line by the sending device is 
correct (we can see this on a console terminal) so it is clear that the 
corruption is happening within the  ATMega. We also read the ATMega UART 
registers and figured out that Frame Errors were occuring. The baud rate was 
38400. We brought it down to 9600 but the problem still persists. One of the 
suspects is the clock stability; we are using the internal RC oscillator of the 

Have UART data corruption issues been seen when using the internal oscillator? 
At what baud rates? 

We have Atmel's application  notes for calibration of the internal RC 
oscillator but we need some time to try that out. 

Has anyone tried out calibrating the internal RC oscillator ? If so, any tips ?

Operating conditions: 3.3V 25C internal RC oscillator.


-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Uwe Fechner
Sent: Thursday, April 06, 2006 4:55 AM
To: AVR-GCC-list
Subject: Re: [avr-gcc-list] Re: ATmega168 FreeRTOS code

David VanHorn wrote:
> Just for grins, the internal RC isn't all that stable over temperature 
> and VCC variations. While you can tweak the osc in at a given temp and 
> VCC, it will drift out again as these change. You should at least use 
> a resonator if you are doing serial comms.
Well, this would not be good for my concept reducing power supply current.
Only RC oscillator is fast enough to start, to make it possible, to have about 
50..100 ┬Ás aktive cpu time every 2 ms.

The improvement, that is still missing, is to recalibrate the RC oscillator at 
runtime using the quarz driven rtc.


Uwe Fechner

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