Failed to read i2c device's register with MATLAB Support Package for Raspberry Pi Hardware

Hi everyone. I would like to read a i2c device's register which is connected to a raspberry pi 4b, and I use the support package for raspberry pi hardware. I follow the help document to creat a i2cdev object, then use readRegister command to read, but no matter what register I choose, the returned data is alway zero. Here are the codes:

>> mypi=raspi;
>> imu = i2cdev(mypi,'i2c-1',0x55);
>> readRegister(imu,0x3d,2)

ans =

  1×2 uint8 row vector

   0   0

However, I can successfully read the nonzero data of the same register in Linux console with i2cget command:

Did I miss something?

[FlyWing]

Just to add that I used matlab 2020b, and the raspberrypi 4b was loaded with the mathwork raspbian image of version R20.2.0. I aslo tried matlab 2019b to connect raspberry pi 3b+ with the mathwork raspbian image of version R19.2.0, but the above problem didn't show up.

Answer 1

[MathWorks MATLAB Hardware Team]

Hi FlyWing,

Can you please perform following steps and see in all three cases you are getting same values, if not then please contact us using this link https://www.mathworks.com/support/contact_us.html

Note: I have used I2C Peripheral address as 0x5c and Read Register address as 0x2a. You can use 0x55 Peripheral address and 0x3d Read Register address when you try following steps.

Please have a fresh instance of R2020b MATLAB and reboot your Raspberry Pi before proceeding ahead.

(1) Create a raspi object in MATLAB and call readRegister on i2cdev object (like how you did before).

(2) Go to putty terminal and execute "$ i2cget -y 1 0x5c 0x2a w" . Use required addresses here.

(3) Use attached myfile.c to compile and execute to see the register values, here are the steps

* In Putty terminal create a new file using "$ sudo nano myfile.c"

* This opens up a Nano editor, copy the contents of attached file and paste in the editor

* Please change the code in myfile.c to required peripheral address and register address.

* Press 'Ctrl+c' and click yes to save the file

* Now compile and build the myfile.c using "$ gcc -o myfile myfile.c"

* Run the generated binay using "$ chmod +x myfile" and "$ ./myfile"

* You should see the peripheral address, register address and data in the terminal.

Regards,

MathWorks MATLAB Hardware Team

[FlyWing]

Thanks for your quick reply.

I tried your suggested steps, and unfortunately I got different values.

For step (1):

For step (2) and (3):

-----------------------------------------------------------------------------------------------------------------------------------------

Note that your C file cannot be successfully compiled on my raspi 4b board, the error is:

But this problem can be solved if I add 'linux/i2c.h' to the headfile. I noticed that your test board is raspi 3b, and mine is raspi 4b. So I guess this problem maybe caused by the hardware difference.

Moreover, I also tested raspi board 3b+. The i2cget command always works. The i2cdev read problem would show up if I still use mathworks raspbian image of R20.2.0, but will disapper if I use the image of R19.2.0.

Would you like me to report this problem as a bug through the link you mentioned?

[MathWorks MATLAB Hardware Team]

Hi FlyWing,

Can you please report this? Also include necessary details of the I2C peripheral which you are using.

Regards,

MathWorks MATLAB Hardware Team

[FlyWing]

OK, thanks again.