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Re: [avr-gcc-list] eeprom usage

From: David Breeze
Subject: Re: [avr-gcc-list] eeprom usage
Date: Thu, 31 Oct 2002 08:08:34 +0000


As you can see from the code below, extracted from eeprom.s, the first check is 
to see if the eeprom is ready, so your code is safe.
        .global _U(eeprom_wb)

        sbic    EECR, EEWE
        rjmp    _U(eeprom_wb)   /* make sure EEPROM is ready */
#ifdef EEARH
        out     EEARH, addr_hi
        out     EEARL, addr_lo
        out     EEDR, val
        in      __tmp_reg__, SREG
        cli                     ; /* no ints between setting EEMWE and EEWE */
        sbi     EECR, EEMWE
        sbi     EECR, EEWE
        out     SREG, __tmp_reg__
#undef val
#endif /* L_eeprom_wb */

The 323 data sheet gives details of EECR and EEWE.

David Breeze

>>> Jamie Morken <address@hidden> 30 October 2002 23:59:10 >>>

I read the datasheet for the AVR I am using (atmega323)
and it gave an eeprom write time of 3.8ms (MAX)
I tested the below code out and it works fine.  
Is a delay built into the read/write functions or am I just pushing the 
limits of the eeprom?  Is this safe?  I already wrote out the code to 
read/write 16 byte messages to eeprom one byte every 5ms
(ironically that code doesn't work but the below does)

Jamie Morken

    eeprom_wb(0, 123);
    eeprom_wb(1, 124);
    eeprom_wb(2, 125);
    eeprom_wb(3, 126);
    eeprom_wb(4, 127);
    eeprom_wb(5, 128);
    eeprom_wb(6, 129);
    eeprom_wb(7, 130);

    printf("eeprom0 = %i\r", eeprom_rb(0));
    printf("eeprom1 = %i\r", eeprom_rb(1));
    printf("eeprom2 = %i\r", eeprom_rb(2));
    printf("eeprom3 = %i\r", eeprom_rb(3));
    printf("eeprom4 = %i\r", eeprom_rb(4));
    printf("eeprom5 = %i\r", eeprom_rb(5));
    printf("eeprom6 = %i\r", eeprom_rb(6));
    printf("eeprom7 = %i\r", eeprom_rb(7));

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