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Re: [avr-gcc-list] Macro to read /write long to eeprom

From: Peter Bosscha
Subject: Re: [avr-gcc-list] Macro to read /write long to eeprom
Date: Wed, 10 Aug 2005 07:46:36 +0200

Slightly off-topic but a handy tip:
For eeprom, perform a read before write, every byte takes 9milisec (Mega128) to write.
So, if you have sequential writes you could spend waiting quite a bit.
We have large structures in eeprom, parts of which are saved/updated regularly. Doing a read before write saved us seconds in wait time.
In my case I implemented simple calls like eeprom_rwb (read-write-byte), the stack & code size overhead are trivial compared to the time saved.

>>> "Royce Pereira" <address@hidden> 09/08/2005 21:36 >>>

On Wed, 10 Aug 2005 00:41:20 +0530, Dave Hansen <address@hidden> wrote:

> From: "Royce Pereira" <address@hidden>
>> Hi,
>> Is there a macro to read or write a long word (32 bits) to eeprom?
>> For the last hour I've been trying to write one unsuccessfully.
> Not directly, but you can do something like
>    #include <avr/eeprom.h>
>    inline void eeprom_write_long(long *dest, long val)
>    {
>       eeprom_write_block(&val, dest, sizeof(val));
>    }
>    inline long eeprom_read_long(long *src)
>    {
>       long retval;
>       eeprom_read_block(&retval, src, sizeof(retval));
>       return retval;
>    }
> WARNING: untested code, but it should be close.  Note that (IMHO) 
> eeprom_write_block's parameters are backwards, but that's what's been 
> provided.
Actually I managed something with the existing word rd/wr macros. But I've 
yet to see how the code size compares with the read/write block method..

uint32_t eeprom_read_long( uint16_t *loc)
        uint32_t num;
        num = eeprom_read_word((uint16_t *)(loc+1));
        num <<=16;
        num |= eeprom_read_word((uint16_t *)loc);
        return num;
void eeprom_write_long(uint16_t *loc, uint32_t val)
        eeprom_write_word(loc, val & 0xffff);
        eeprom_write_word(++loc, val >>16);


Thanks, all,

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