Gentlemen,
We are trying to use i2c tools for Linux for our application and encountered a problem:
Read and write of Microchip 24AA256 device, which is used as our fan tray
EEPROM, requires sequences of i2c operations which seem to be not fully supported by
current i2c-dev driver of Linux kernel.
To read a byte from 24AA256 one has to perform:
( -> from master to slave; <- from slave to master)
-> START
-> Control Byte (1010 0000)
<- ack
-> Address High Byte
<- ack
-> Address Low Byte
<- ack
-> START
-> Control Byte (1010 0001)
<- ack
-> Dummy byte
<- Data byte
<- NO ack
-> STOP
To write a byte to 24AA256:
-> START
-> Control Byte (1010 0010)
<- ack
-> Address High Byte
<- ack
->Address Low Byte
<- ack
<<<---------- no -> START <<-------
-> Data byte
<- ack
-> STOP
Macros provided in i2c-dev.h do not give us ability to write 2-byte address for both read
and write single byte data.
It also does not give us ability to avoid START in write operation.
We found a work-around for read by doing a small trick:
A. Perform a Byte write to the EEPROM:
- Slave address is the EEPROM address, Write address is the high 7 bits of
the address, Data is the low 7 bits of the address.
B. Perform a Byte read from the EEPROM:
- Slave address is the EEPROM address
We do not have a trick to avoid START in a write operation.
Can you suggest anything as a work-around?
Vladimir Cherednichenko
Sr. Software Engineer
CloudShield Technologies, Inc.
212 Gibraltar Drive
Sunnyvale, CA 94089
vcherednichenko at cloudshield.com.
408 331 6692 direct
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