Hi,
I try to use the at24 eeprom driver on top of this driver.
This EEPROM (24c32) works with two address bytes.
Writing results in a call to at91_twi_xfer() with num=1.
In this case the internal address register is not used and the address is sent out within the buffer.
Reading results in a call to at91_twi_xfer() with num=2.
In this case the internal address register is used.
However the MSB of the internal address resides in msg->buf[0] and the LSB resides in msg->buf[1] of the first message.
As a result the code:
+ for (i = 0; i < msg->len; ++i) {
+ internal_address |= ((unsigned)msg->buf[i]) << (8 * i);
+ int_addr_flag += AT91_TWI_IADRSZ_1;
+ }
+ at91_twi_write(dev, AT91_TWI_IADR, internal_address);
constructs an internal address in a wrong byte order.
Example: Try to read from address 0x100:
msg[0]->buf[0] = 0x1;
msg[0]->buf[1] = 0x0;
results in
internal_address = 0x1;
I think it must be:
+ for (i = 0; i < msg->len; ++i) {
+ internal_address |= ((unsigned)msg->buf[msg->len-1-i]) << (8 * i);
+ int_addr_flag += AT91_TWI_IADRSZ_1;
+ }
+ at91_twi_write(dev, AT91_TWI_IADR, internal_address);
... or the at24 eeprom driver constructs the wrong internal address ...
Mit freundlichen Grüßen / Best regards
Carsten Behling
Development Engineer
Garz & Fricke GmbH
Tempowerkring 2, 21079 Hamburg - Germany
Amtsgericht Hamburg HRB 60514
Geschäftsführer: Manfred Garz, Matthias Fricke
Phone: +49 (0) 40 791 899 - 56
Fax: +49 40 / 791 899 - 39
www.garz-fricke.com
-----Ursprüngliche Nachricht-----
Von: Voss, Nikolaus [mailto:N.Voss@xxxxxxxxxxx]
Gesendet: Mittwoch, 23. November 2011 11:29
An: Carsten Behling
Cc: 'linux-i2c@xxxxxxxxxxxxxxx'; 'linux-arm-kernel@xxxxxxxxxxxxxxxxxxx'; 'linux-kernel@xxxxxxxxxxxxxxx'
Betreff: RE: [PATCH v5 3/4] drivers/i2c/busses/i2c-at91.c: add new driver
Hi,
Carsten Behling wrote on 2011-11-23:
>> this case is already catched in at91_do_twi_transfer():
>
> Sorry, I did not found this code in your patch.
> (http://www.mail-archive.com/linux-i2c@xxxxxxxxxxxxxxx/msg06556.html):
>
>> + if (is_read) {
>> + if (!dev->buf_len)
yes, this won't work for buf_len == 1. It is corrected in
https://lkml.org/lkml/2011/11/18/223 which I held back for some time
as it should have been just a feature extension. I was not aware it
also fixed the buf_len = 1 bug. Sorry for that...
(Explanation: in the first implementation I immediately decremented
buf_len, so buf_len == 1 could not occur. Later I removed that but
did not fully fold it into the base patch.)
Thanks,
Niko
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