Date: Wed, 22 May 2019 15:14:52 -0700 (PDT) From: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net> To: Ian Lepore <ian@freebsd.org> Cc: Karl Denninger <karl@denninger.net>, freebsd-arm@freebsd.org, Prasad M <mprasad9689@gmail.com> Subject: Re: FreeBsd I2C utility gives same value as MSB and LSB from DS75 sensor 16bit register. Message-ID: <201905222214.x4MMEq9b086987@gndrsh.dnsmgr.net> In-Reply-To: <e430da11ed01f26197adf92c3ab53aba0813ee02.camel@freebsd.org>
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> On Wed, 2019-05-08 at 14:06 -0500, Karl Denninger wrote: > > On 5/3/2019 06:43, Prasad M wrote: > > > Hi Folks, > > > > > > I am trying to access a DS75 I2C temperature sensor. It kind of works with > > > the default i2c utility. But it returns twice the high byte instead of the > > > high and low byte for the temperature. Probably because it does 1 byte > > > reads on the I2C bus, sending a stop condition after every byte. > > > > > > The device expects continuous reads and no stop/start in between the 2 > > > bytes. Trying all options i2c, most notably the -m mode switch, yields the > > > same results all the time. Looking at the code in i2c.c > > > > > > Could any one help to solve this problem with working I2CRDWR utility. > > > > I don't know if you can do it with that utility, but coding up a simple > > (~10-15 lines of "C") that reads two bytes is trivially easy. > > > > You simply stuff a message buffer requesting 2 bytes in response and > > call ioctl; you get back two bytes. > > > > This should now be fixed as of r348120 in 13-current, which I will MFC > to 12-stable after it gets some testing. The fix adds a new "-m tr" > mode. 'tr' is for "transfer", a mode in which the complete set of i2c > operations are all handed to the driver at once using I2CRDWR, rather > than doing a set of individual START/REPEAT/STOP commands from > userland. Some drivers (such as rpi) only work with complete > transfers. > > So, to read the temperature from a DS75, it should now work like: > > i2c -m tr -a 0x40 -d r -o 0 -w 8 -c 2 Thank you, I think this is going to be well used! > -- Ian -- Rod Grimes rgrimes@freebsd.org
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