From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Buehl Date: Wed, 06 Mar 2013 22:02:41 +0000 Subject: [lm-sensors] Support for non-register devices Message-Id: <5137BD01.6080905@buehltech.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lm-sensors@vger.kernel.org I am new to using I2C so apologies if this has already been addressed before. In trying to communicate with a Honeywell HIH-6130 humidity sensor from a RaspberryPi I ran into an apparent limitation of i2c-tools. There doesn't seem to be support for reading multiple bytes of data from a device that doesn't need a register selected before the read. This device is accessed by first doing a write of just the address, followed about 37ms later by a read of 4 bytes, as documented here http://www.phanderson.com/arduino/I2CCommunications.pdf. The write operation can be done by using write_quick(), and a subsequent read_byte() will get the first byte of data, but multiple calls to read_byte() will just get the same first byte again. Using read_i2c_block_data() works better, however, because it sends an unneeded command byte, I'm not sure the data returned is valid. There is a long discussion of the details in this thread http://www.raspberrypi.org/phpBB3/viewtopic.php?f2&t)454. It seems to me that what is needed is a way to optionally specify that no command byte should be sent in read_i2c_block_data() and write_i2c_block_data(). While this is not compliant with the SMBus protocol, this device doesn't claim to be compliant, and the purpose of these two functions seems to be to allow such communications. I don't believe this particular device is unique so there should be other cases where this is useful. I looked at the python wrapper code in smbusmodule.c and it looks easy enough to implement something like specifying a value of None for the cmd argument to indicate that no command byte should be sent, but implementation of the behavior seems to be buried somewhere deep in i2c-dev.c or i2c-core.c and I haven't been able to find it. I see that there is work being done in this project to clean up these drivers, so I wanted to propose this change, and also offer my help. _______________________________________________ lm-sensors mailing list lm-sensors@lm-sensors.org http://lists.lm-sensors.org/mailman/listinfo/lm-sensors