Re: [avr-gcc-list] External EEPROM verses internal EEPROM data handling

[Steven Michalske]

so your external EEPROM will be accessed by functions you write.  The  
compiler does not know how to interface to the external EEPROM.

The functions you will need will take a pointer to your data structure  
and then pack it into the external EEPROM, the other will take a  
pointer and extract the data from the EEPROM into the structure.  Both  
of these functions will need some method for addressing your EEPROM's  
internal memory

I would suggest that instead of an external I2C EEPROM, that you get a  
SD card and put a file system on it and append to a text file for your  
log, Ahh, 1GB of space to work with and CHEAP.

EVEN if you don't use a filesystem it would be effective.

Steve

On May 4, 2009, at 1:55 AM, Prashant D. Kharade wrote:

> Hello,
>
> I am relatively new, not only to Atmel but also to Embedded system.
> I am doing my first embedded project, 24 channel Data-Logger system.
> This is Time based data logging system.
> We are supposed to log the data after every 15 min.
> After each 15 min, 58 bytes of data is supposed to be saved.
> The data structure is as follows.
>
> typedef struct eventdata
>         {       uint8_t unit_add;
>                 uint8_t card_add;
>                 uint8_t event_no;               //Event counter
>                 uint8_t type;           //Event type
>                 uint8_t year;           //rtc yesr
>                 uint8_t month;          //rtc month
>                 uint8_t day;            //rtc day
>                 uint8_t hour;           //rtc hour
>                 uint8_t min;            //rtc min
>                 uint8_t sec;                    //rtc sec
>                 uint16_t voltage[24];   // adc counts of 24 channels in an array
>         } ED;           // total data = 58 bytes
> ED ramdata;                             // current event data in ram
> ED temp_ramdata;			// load eeprom data to this event data for  
> sending to uart	
> ED EEMEM eepdata[60];                   // 60 events data on EEprom
>
> I am saving this in EEPROM of Atmega128 microcontroller. Each event  
> require 58bytes. Atmega128 has max 4K EEPROM.
> So I can save 4K/58 = 70 events at max.
>
> But now I am supposed to save around 500 events.
> So Internal EEPROM cannot be used. So we decided to use EXternal  
> EEPROM on I2C bus.
> I found the readymade library from Peter Fleury on the net.
>
> But I faced following problems.
> 1. How to declare "ED EEMEM eepdata[60];" (60 events data on EEprom)  
> on External memory.
> 2. Whenever a  time event occurr all the data is stored in RAM (ED  
> ramdata). Then in a single command this data was transferred to the  
> EEPROM as follows
>   eeprom_write_block((const void*)&ramdata, 
> (void*)&eepdata[event_count-1], sizeof(ED));
>   Now if I use the external EEPROM, how shall I send structure type  
> ED ?
> 3. Infact, I have stored data such as calibration, initial data in  
> structures. And transfer the data very easily from RAM to EEPROM &  
> viceversa.
> 4. When any data to be read from EEPROM, I used the command
> eeprom_read_block((void*)&temp_ramdata,(const  
> void*)&eepdata[t_event_no-1], sizeof(ED));
>
> I do not know how to declare EEPROM variables, or how to use above  
> commands in external EEPROM.
> I am feeling now, the external EEPROM data handling is very difficult.
> How to make it simple. Could you please suggest some good logical  
> ideas.
>
> Thanks
>
> Prashant
>
>
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