Date: Thu, 1 Dec 2016 10:11:04 +0000 From: Nick Hibma <Nick@ip-knowhow.com> To: =?Windows-1252?Q?=93FreeBSD_Embedded_Mailing_List=94?= <freebsd-embedded@FreeBSD.org> Subject: Questions about i2c.c (TMP102 temperature sensor) Message-ID: <9424D7FD-C4B6-43D5-A0C5-76D5BE9ED1DE@ip-knowhow.com>
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Gents,
I am not quite sure who to owner of i2c.c is, so perhaps some I2C enthousia=
st could help me with the following problem.
I was trying to access a TMP102 I2C temperature sensor. It kind of works wi=
th the default i2c utility. But it returns twice the high byte instead of t=
he high and low byte for the temperature. Probably because it does 1 byte r=
eads on the I2C bus, sending a stop condition after every byte. This was ve=
rified with a logic analyser.
The device expects continuous reads and no stop/start in between the 2 byte=
s. Trying all options i2c, most notably the -m mode switch, yields the same=
results all the time. Looking at the code in i2c.c I get confused as it s=
eems to somehow fiddle with start/stop to get it right because of the -m sw=
itch, but uses read() in the end to get the data, not I2CREAD.
fd =3D open(dev, O_RDWR);
if (i2c_opt.width) {
error =3D ioctl(fd, I2CSTART, &cmd);
error =3D ioctl(fd, I2CWRITE, &cmd);
if (i2c_opt.mode =3D=3D I2C_MODE_STOP_START) {
error =3D ioctl(fd, I2CSTOP, &cmd);
}
}
if (i2c_opt.mode =3D=3D I2C_MODE_STOP_START) {
error =3D ioctl(fd, I2CSTART, &cmd);
} else if (i2c_opt.mode =3D=3D I2C_MODE_REPEATED_START) {
error =3D ioctl(fd, I2CRPTSTART, &cmd);
}
/******** Without i2c_opt.width set there is no START condition either to s=
et the slave address for the read() ****/
/******** Why this stop? ***/
error =3D ioctl(fd, I2CSTOP, &cmd);
for (i =3D 0; i < i2c_opt.count; i++) {
error =3D read(fd, &i2c_buf[i], 1);
}
close(fd);
I would have expected:
fd =3D open(dev, O_RDWR);
if (i2c_opt.width) {
error =3D ioctl(fd, I2CSTART, &cmd);
error =3D ioctl(fd, I2CWRITE, &cmd);
if (i2c_opt.mode =3D=3D I2C_MODE_STOP_START) {
error =3D ioctl(fd, I2CSTOP, &cmd);
error =3D ioctl(fd, I2CSTART, &cmd);
} else if (i2c_opt.mode =3D=3D I2C_MODE_REPEATED_START) {
error =3D ioctl(fd, I2CRPTSTART, &cmd);
}
} else {
/***** Use START/STOP to set the slave address for the read() below ***/
error =3D ioctl(fd, I2CSTART, &cmd);
error =3D ioctl(fd, I2CSTOP, &cmd);
}
error =3D ioctl(fd, I2CREAD, &cmd); // read all bytes in one go
error =3D ioctl(fd, I2CSTOP, &cmd);
close(fd);
Any opinions on where I am wrong?
Second question:
Rolling my own little program with this change fails because I cannot get I=
2CREAD to work. It keeps returning EIO. Some other web pages claim that the=
re is an implementation problem with that. Using read() on the fd works fin=
e, so do get a valid temperature out of the device now.
Cheers,
Nick Hibma
--
ip-knowhow
E: nick@ip-knowhow.com<mailto:nick@ip-knowhow.com>
T: +31 (0)85 2010923
M: +31 (0)6 14433161
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