Graham,
The part number is AT24c256 and a quick jot over to Atmel's trusty website
and I found the spec sheet... "256K Serial Eeprom... organized as 512 pages
of 64 bytes each."
So, that should mean 512x64 = 32,768 bytes... .32K.
256k bits = 262,144 / 8 = 32,768 bytes... 32k.
It's most certainly a 32k-byte part.
Thanks,
Bryan
On Friday, July 15, 2016 at 11:45:02 AM UTC-5, Graham wrote:
> Brian:
>
> You need to learn to speak "marketing" and "binary".
>
> A 32 k EEPROM (named by marketing) is a 32k BIT EEPROM.
>
> 32k BITs divided by 8 bits-per-byte is 4k BYTES.
>
> 4k BYTES is 0x1000 BYTES.
>
> So, your address space wraps around every 0x1000 BYTES.
>
> The data is not repeated every 0x1000 bytes, it is the SAME data.
>
> Sounds like your EEPROM is working just fine.
>
> --- Graham
>
> ==
>
> On Friday, July 15, 2016 at 10:47:54 AM UTC-5, Bryan Wilcutt wrote:
>>
>> I've been playing with the BBB 32k eeprom by reading and writing data to
>> it. I use fseek(), fopen(), fread() and fwrite(). The device I am
>> reading/writing/opening is:
>> /sys/bus/i2c/devices/0-0050/at24-0/nvmem
>>
>> This does seem to work however not well. I noticed that the same data
>> is repeated every 0x1000 bytes. Why is that? Am I not addressing the part
>> correctly? Since I'm ultimately using the at24.c driver, I inspected it
>> and it does seem to attempt to translate addresses for the part. Are there
>> specific limitations with at24 that I should be aware of, nothing seems to
>> be documented that I've seen.
>>
>> #define e2FILE "/sys/bus/i2c/devices/0-0050/at24-0/nvmem"
>>
>> int readEEPROMAt(unsigned char *p, unsigned int startAddr, unsigned
>> int len)
>> {
>> int retVal = 0;
>> FILE *fp = NULL;
>>
>> if ((fp = fopen(e2FILE, "r")) != NULL)
>> {
>> if (fseek(fp, startAddr, 0) == 0)
>> {
>> if (fread(p, 1, len, fp) != len)
>> printf("Error: Cannot read EEPROM\n");
>> else
>> retVal = 1;
>> } else {
>> printf("Error: Could not index EEPROM, no data read.");
>> }
>> } else {
>> printf("Error: Cannot open EEPROM\n");
>> }
>>
>> if (fp)
>> fclose(fp);
>>
>> return retVal;
>> }
>>
>> Bryan
>>
>>
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