Using Raspberry Pi software i2c bus with MATLAB

Hi,

I am running MATLAB 2019a and the MATLAB Support Package for Raspberry Pi HardwareMATLAB Support Package for Raspberry Pi Hardware. I need to use a software i2c bus on the Raspberry Pi 3B+ to connect to an BNO055 IMU, as it requires that clock stretching be supported by i2c to transmit data.

I have activated it by adding:

dtoverlay=i2c-gpio,bus=3,i2c_gpio_sda=23,i2c_gpio_scl=24

in the file /boot/config.txt

After connecting to the Rpi using the raspi command, only hardware bus is available. If a execute an i2c scan from the command line using the system function I have:

>> system(rpi,'/usr/sbin/i2cdetect -y -r 3')

ans =

' 0 1 2 3 4 5 6 7 8 9 a b c d e f

00: -- -- -- -- -- -- -- -- -- -- -- -- --

10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

20: -- -- -- -- -- -- -- -- 28 -- -- -- -- -- -- --

30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

70: -- -- -- -- -- -- -- --

'

When I try to connect to the sensor with address 0x28 y have the following error:

>> imu_bmo055 = i2cdev(rpi,'i2c-3','0x28')

I2C bus i2c-3 is not available. Use AvailableI2CBuses property of the raspi object to see a list of available I2C buses.

Is it possible to add the new i2c bus to the list of AvailableI2CBuses or it only works with hardware i2c buses?

Thank you very much.

[Prasanth Sunkara]

Hello Rafael,

Please try adding the i2c-3 bus parameters in the below file.

>> edit (fullfile(raspi.internal.getRaspiRoot, 'raspi', 'internal', 'boardInfoRaspberryPi3ModelBPlus'))

After line 30, try adding the third i2c bus like below.

info.Board.I2C(3).Name   = 'i2c-3';
info.Board.I2C(3).Number = 1;
info.Board.I2C(3).Pins   = [23, 24];   % SDA, SCLK

Let me know if this works.

Thanks,

Prasanth

Answer 1

[Rafael Gonzalez de los Reyes]

Hello Prasanth,

Thank you very much for your kind answer. I have just tried your solution and I am going to comment the results.

1) The i2c-3 bus appears as available, but there is a warning about detecting bus speed:

>> rpi = raspi

Warning: Cannot query I2C bus speed.

> In raspi.internal.raspiBase/getAvailablePeripherals (line 899)

In raspi.internal.raspiBase (line 172)

In raspi.internal.raspiDesktop (line 98)

In raspi (line 72)

rpi =

raspi with properties:

DeviceAddress: '169.254.0.2'

Port: 18734

BoardName: 'Raspberry Pi 3 Model B+'

AvailableLEDs: {'led0'}

AvailableDigitalPins: [4,5,6,12,13,14,15,16,17,18,19,20,21,22,25,26,27]

AvailableSPIChannels: {'CE0','CE1'}

AvailableI2CBuses: {'i2c-1','i2c-3'}

AvailableWebcams: {'mmal service 16.1 (platform:bcm2835-v4l2):'}

I2CBusSpeed:

Supported peripherals

By default it should be the same as for i2c-1 bus

2) If a scan the bus from MATLAB, no device is detected:

>> scanI2CBus(rpi,'i2c-3')

ans =

0×0 empty cell array

But if I open a shell window and use i2ctools, I get:

$ i2cdetect -y -r 3

0 1 2 3 4 5 6 7 8 9 a b c d e f

00: -- -- -- -- -- -- -- -- -- -- -- -- --

10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- --

70: -- -- -- -- -- -- 76 --

Best regards,

Rafael

[Prasanth Sunkara]

scanI2CBus - uses "i2cdetect -y <bus number>" command under the hood.

If adding an additonal "r" helped in your case, I would suggest adding the -r flag in "scanI2CBus" method of "raspi.internal.raspiBase" file. (>> edit raspi.internal.raspiBase)

Please let me know the results.

Thanks,

Prasanth

[Rafael Gonzalez de los Reyes]

I have tried but it doesn't work. I have also been looking around the code in raspi.internal.addiraspiBase and I tried adding this lines:

try

% i2c_gpio is a platform-independent bitbanging I2C driver

execute(obj.Ssh,'/sbin/modinfo i2c_gpio');

i2cModules = [i2cModules ,{'i2c_gpio'}];

catch

end

around line number 310, but it doesn't work either. In fact, executing modinfo with parameter i2c_gpio gives the following result:

$ /sbin/modinfo i2c_gpio

filename: /lib/modules/4.14.79-v7+/kernel/drivers/i2c/busses/i2c-gpio.ko

alias: platform:i2c-gpio

license: GPL

description: Platform-independent bitbanging I2C driver

author: Haavard Skinnemoen (Atmel)

srcversion: 7BD8B1C09C09D38E24E9D11

alias: of:N*T*Ci2c-gpioC*

alias: of:N*T*Ci2c-gpio

depends: i2c-algo-bit

intree: Y

name: i2c_gpio

vermagic: 4.14.79-v7+ SMP mod_unload modversions ARMv7 p2v8

As you can see, there is no baudrate parameter. I guess that the code basically centres on hardware modules. I have checked that i2c_gpio is active:

$ cat /proc/modules | grep i2c

i2c_bcm2835 16384 0 - Live 0x7f199000

i2c_gpio 16384 0 - Live 0x7f16e000

i2c_algo_bit 16384 1 i2c_gpio, Live 0x7f15d000

i2c_dev 16384 0 - Live 0x7f09f000

Anyway, I would like to tell you that I am not going to be able to use MATLAB in next couple of weeks (some delays with licence renewal from my University, I have been told that it won't be ready until February 10th or so and there is only one day left).

Thank you very much for your help. As soon as I can work regularly with MATLAB I will let you know. Meanwhile, I am going to have a look at raspiBase and also I am going to try to define a baudrate for i2c-3 bus.

Best regards,

Rafael