multi byte i2c with current interface, is it possible?

ypapelis

I am trying to read a pololum 9 DOF imu (http://www.pololu.com/catalog/product/1264/resources) using the i2c driver in propgcc.

One problem I run into, is that if I use the simple_i2cOpen call, I can't get any devices to respond. The same setup can talk to all three sensors using SPIN so I know that from a hardware standpoint things are intact.

I used instead the i2cOpen, but when the magnetometer requires that six bytes be read in a multi-byte sequence, without resending the start bit. I can't see how I can do this since the i2c interface does not expose the low level start/stop bit functionality (except for specifying if the ack-bit should be set or not).

I have SPIN code that will read the mag fine but I am trying to avoid bit-banging the i2c bus and want to use the built-in driver. Is it possible to do so?

David Betz

ypapelis wrote: »

I am trying to read a pololum 9 DOF imu (http://www.pololu.com/catalog/product/1264/resources) using the i2c driver in propgcc.

One problem I run into, is that if I use the simple_i2cOpen call, I can't get any devices to respond. The same setup can talk to all three sensors using SPIN so I know that from a hardware standpoint things are intact.

I used instead the i2cOpen, but when the magnetometer requires that six bytes be read in a multi-byte sequence, without resending the start bit. I can't see how I can do this since the i2c interface does not expose the low level start/stop bit functionality (except for specifying if the ack-bit should be set or not).

I have SPIN code that will read the mag fine but I am trying to avoid bit-banging the i2c bus and want to use the built-in driver. Is it possible to do so?

I'm not sure what's happening with the simple i2c driver but both of them should only set the start condition at the beginning of a byte sequence. If you specify a byte count of greater than one and supply the right size buffer you should get a sequence of bytes with no start or stop conditions in the middle.

I2C *dev;
uint8_t buffer[4];
int address;

i2cRead(dev, address, buffer, sizeof(buffer), TRUE);

ypapelis

David Betz wrote: »

I'm not sure what's happening with the simple i2c driver but both of them should only set the start condition at the beginning of a byte sequence. If you specify a byte count of greater than one and supply the right size buffer you should get a sequence of bytes with no start or stop conditions in the middle.

I2C *dev;
uint8_t buffer[4];
int address;

i2cRead(dev, address, buffer, sizeof(buffer), TRUE);

Thanks Dave, that makes sense; after I posted I realized that I can just stick more bytes in the buffer, specify the size and it should work.

I think the multi-byte works now but I am still not getting correct data from the sensors. Data comes out, but it's not correct.

I was also wondering about the last argument to the i2copen() function, is it the actual data rate (i.e., 400000) or a symbolic constant? It would be great to have some functioning examples with actual devices so some of these things become clear, but i guess all in due time ...

Thanks again !

David Betz

ypapelis wrote: »

Thanks Dave, that makes sense; after I posted I realized that I can just stick more bytes in the buffer, specify the size and it should work.

I think the multi-byte works now but I am still not getting correct data from the sensors. Data comes out, but it's not correct.

I was also wondering about the last argument to the i2copen() function, is it the actual data rate (i.e., 400000) or a symbolic constant? It would be great to have some functioning examples with actual devices so some of these things become clear, but i guess all in due time ...

Thanks again !

The last parameter is supposed to be the actual data rate although it may not be exact. 400000 is the maximum that it supports at the moment.

David Betz

ypapelis wrote: »

Thanks Dave, that makes sense; after I posted I realized that I can just stick more bytes in the buffer, specify the size and it should work.

I think the multi-byte works now but I am still not getting correct data from the sensors. Data comes out, but it's not correct.

I was also wondering about the last argument to the i2copen() function, is it the actual data rate (i.e., 400000) or a symbolic constant? It would be great to have some functioning examples with actual devices so some of these things become clear, but i guess all in due time ...

Thanks again !

Here is an example that talks to an ADC chip.

tlperrine

David,

Is it possible to post or point me to examples of c code that uses the i2copen, i2cread, and i2cwrite application program interfaces. I am trying to communicate with the altimeter module MS5607 and compass module 3 axis HMC5883L.

Thanks,
Terry

David Betz

tlperrine wrote: »

David,

Is it possible to post or point me to examples of c code that uses the i2copen, i2cread, and i2cwrite application program interfaces. I am trying to communicate with the altimeter module MS5607 and compass module 3 axis HMC5883L.

Thanks,
Terry

I'm afraid that I rewrote my i2c sample code for the PropBOE ADC to use my new ADC driver so I don't have the old code that used the i2c driver directly anymore. I'll try to dig through my archives and find it. Sorry for the delay.

David Betz

tlperrine wrote: »

David,

Is it possible to post or point me to examples of c code that uses the i2copen, i2cread, and i2cwrite application program interfaces. I am trying to communicate with the altimeter module MS5607 and compass module 3 axis HMC5883L.

Thanks,
Terry

Here is some code I wrote a while back that uses the i2c library functions. Unfortunately, It talks to the Parallax compass sensor.

tlperrine

David,

Thanks alot. With a couple of minor tweeks, that did the trick.

Terry

David Betz

tlperrine wrote: »

David,

Thanks alot. With a couple of minor tweeks, that did the trick.

Terry

Great! I'm glad it was helpful.