atmega128 date/time management

By not using a library without exacly knowing what it does. You hope by connecting a GSM to an AVR and calling the time library, the correct time is returned ? How would it ...

Rene

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Rene Tschaggelar a =E9crit :

Hi Rene,

I think you misunderstood what I wanted to say.

I want to get a valid system time in my C program. I have tried to do it with the time library without success. Now, I'm stuck without a valid date and not understanding why. I have looked every where to see what can cause the problem. Doing this, I found that the GSM device connected to the AVR was running ok and giving a clock time. I never said that connecting both will make the AVR return a correct time.

Reading your answer, I guess that my ideas about the time library are probably wrong. Do you have any hints to "guide" me ?

Didrik

You say you have connected the GPS and know the GPS is receiving the correct time, you have not said how you have implemented the time() function in order that it too reads the time from the GPS.

time() is a standard function that is implemented differently for each system, depending on how the system measures/stores time. In your case it must be configured to read the GPS. How have you done this?

All you say is that you are calling time(). You have given no information on how you are attempting to obtain the time within this function, so nobody will be able to provide any sort of advice on what is wrong.

Regards, Richard.

for Cortex-M3, ARM7, ARM9, HCS12, H8S, MSP430 Microblaze, Coldfire, AVR, x86, 8051 & PIC18 * * * *

Hi Richard,

Thank you for your answer. Here are some details about the problem

[1] There is no GPS on this hardware. The hardware is the following : Audiotel GSM/GPRS Industrial I/O : the core of the system is a Atmel AVR Atmega128 with a Siemens GSM/GPRS modem. [2] I did not implement any function but only used the official time library provided with IAR Embedded Workbench for Atmel AVR. The project is configured to use the Normal DLIB.

The code I use is the following (i've just extracted the things related to time.h, all the reste is audiotel specific):

#include [...] void MonitorModem( void) { [...] time_t now; time(&now); printf("Time is %s\r\n", ctime(&now)); [...] }

I don't understand that there is no tutorial, howto or FAQ available anywhere that precisely explains how to get and set system time on a atmega128 system. That's why i'm posting a question here.

I was meaning GSM.

From the IAR manual on the library function time(): "If tod is not a null pointer, the function stores the current calendar time in *tod. The function returns the current calendar time, if the target environment can determine it; otherwise, it returns -1."

An AVR has no means of returning time itself. Your hardware has to be designed to include some form of clock (in your case I presume you read it from the GSM interface), then you have to implement the time() function to use that clock.

If you don't do this, where are you expecting the time to come from? AVR's are nice devices, but their telepathy peripherals are a little underdeveloped ;-)

Regards, Richard.

for Cortex-M3, ARM7, ARM9, HCS12, H8S, MSP430 Microblaze, Coldfire, AVR, x86, 8051 & PIC18 * * * *

From reading your responses to others' responses, I think you're being misunderstood.

You say you have an RTC, yet time() is returning -1 (i.e. not set). Logically, you have to set the RTC first, in order for time() to return valid data. How exactly you do this on your platform I have no idea ;).

Steve

Richard,

You're right. This will close the thread. I don't have a RTC on the atmega128. That's why the time() function returns -1. I understood a lot of things about my device this afternoon. Sorry for the waiste of time. But now, there is somewhere on the internet a thread for ignorant guys like me stating that Atmel AVR Atmega128 have no RTC, so they can't give you a valid system time !

Many thanks to all for the information, guidance and enlightenment.

Didrik

Didrik, an Atmega128 is not a system, just a controller. If you want it to do anything sensible you have to do it yourself usually. Even an RTC is not just read by a library, unless this library is specifically made for the cpu and for the RTC with the correct interface (SPI,I2C,twowire). And a hardware realtimeclock doesn't by itself have the correct time. Unless running from an own battery, it looses time and returns garbage.

Rene

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Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

It doesnt have a RTC. Get a two wire interface RTC and use the SCL SCA lines