Communication with SPI device connected to an arduino due works with matlab, but not with simulink

Hello,

I've got an SPI device (LDC1101 Inductance-to-Digital Converter) connected to an Arduino Due and try to communicate with it using the MATLAB Support Package for Arduino Hardware (2016a). I'm able to read and write registers of the device with matlab, but I would like to deploy a simulink model to the arduino, and I don't get SPI communication working. I have the Simulink Support Package for Arduino Hardware installed.

In matlab, the following code works:

a = arduino();
dev = spidev(a,'D4','Mode',3,'BitOrder','msbfirst','Bitrate',4000000);
%Example for reading all registers of SPI device
data = [];
for i=0:63
  data = [data;{dec2hex(i),dec2bin(AccessLDC(dev,i,0,0))}];
end

function AccessLDC:

function response = AccessLDC(dev,register,data,write)
%Build message for LDC1101
msg = 256*(register + (write==0)*128) + data;

%Write message, 8 lower bits contain response
response = dev.writeRead(msg,'uint16');

%Process message, return 8 lower bits
response = bitand(response,255);

But the attached simulink model does not produce any meaningful results. The matlab Fcn block in the subsystem "AccessLDC" uses the same line of code as in the matlab program.

%Build message for LDC1101
msg = 256*(register + (write==0)*128) + data;

See also the attached configuration parameters of the model. Has anyone a clue of what I'm doing wrong?

[Sudeshna Bhattacharya]

You can click on Configuration Parameters > All Parameters > Block reduction and see if "Block Reduction" is unchecked. If it is checked then the code for SPI block wont be generated.

If it Block Reduction is unchecked then you can try to deploy the arduino_SPI_EEPROM.slx model to any EEPROM and check if it works.

You can also attach the model so that I can have a look.

[Oliver]

Hi,

the Block Reduction was indeed checked, but unchecking didn't resolve the issue. I attached the model, this forum doesn't support uploading .slx files, so I saved as .mdl. I would be glad if you could take a look...

[Sudeshna Bhattacharya]

I think as of now you are trying to just model the AccessLDC function in Simulink as of now that takes data =0 as input and gives response as output. You have not modeled the loop part yet.

So to communicate with the sensor you first create an spidev object with the SPI settings and slave pin in MATLAB. Then you just send 1 uint16 number ("msg = 256*(register + (write==0)*128) + data") to the sensor and expect a uint16 back from sensor and extract the lower 8 bits out of it.

Tell me the following:

1. What does response = dev.writeRead(msg,'uint16') return in MATLAB? 2. What output you get from Simulink SPI block? 3. Just try with other modes in the SPI settings: 0, 1, 4.

Let me know if it works.

[Oliver]

Yes, I tried getting the AccessLDC part working first. The loop in the matlab script is just for demonstration, it reads all registers of the device.

To get a response from the device, one always has to write 16 bits, the first 8 contain the command, then the device writes back 8 bits, which I extract. The simulink block returns only zeros or 255s, depending on the SPI mode I choose (I tried all modes).

I figured that I have to configure the device first, to be sure it operates correctly. If the power supply is lost, the matlab script only works if the device is configured with some write commands:

%SPI Test arduino due
clear
close
a = arduino();
dev = spidev(a,'D4','Mode',3,'BitOrder','msbfirst','Bitrate',4000000);
configLDC = struct('reg',[11 4 2 3 1 50 51 52 48 49 5 12 11],...
                  'data',[1 195 219 127 87 0 0 0 240 0 1 255 0]);
for i=1:length(configLDC.reg)
 AccessLDC(dev,configLDC.reg(i),configLDC.data(i),1);
end

I tried to model this in simulink using a for loop (since the spiwriteread command only accepts vectors up to 8 elements for uint16). But now I get a compile error:

### Build procedure for model: 'SPI_Question2' aborted due to an error.
No appropriate method, property, or field 'SampleTime' for class 'codertarget.arduinobase.internal.arduinoSPIWriteRead'.

[Oliver]

Simulink model for configuring SPI device...error.

### Build procedure for model: 'SPI_Question2' aborted due to an error.
No appropriate method, property, or field 'SampleTime' for class 'codertarget.arduinobase.internal.arduinoSPIWriteRead'.

[Sudeshna Bhattacharya]

This 'SampleTime' related error has been fixed in the latest May release. You can update your Simulink Support Package for Arduino to 16.1.2 and try.

[Oliver]

Hi, the SampleTime related error disappeared after updating to the latest version of the simulink Support Package for Arduino.

I modified the model so that there is a block which executes first to configure the SPI device, and then I read one register continuously. I only get '255' values as output, independent of the SPI mode. Although under matlab the value of the register changes due to noise (as it should be in my case).

[Oliver]

I think I was able to narrow down the problem to a probable cause. I investigated the signals with a logic analyzer, and the slave select pin, which should be low during data transfer, goes high after 8 clock cycles. But to commmunicate with my SPI device, I have to transfer 16 bits without changing the slave select pin to high(see attached screenshot and model). I think this might be a bug in the spiwriteread block...Has anyone an idea for a workaround?

[Sudeshna Bhattacharya]

Ideally if you choose datatype as uint16 then the Slave Select pin should be low for all the 16 bits with SPI WriteRead block. You can take a look at MW_SPIwriteRead.cpp placed under $SUPPORTPACKAGEINSTALLDIR\toolbox\target\supportpackages\arduinobase\src. If you look at the function "MW_SPIwriteReadLoop" > switch case 2 (for uint16) > under the condition if _ROTH_DUE you can find that after sending first set of 8 bits (depending on the bit order) SPI_CONTINUE is sent and then the last 8 bits.

Can you try your logic in Arduino IDE and compare with this CPP file's logic?

[Oliver]

I worked around my problem with writing a s-function. Thank you anyway.

[tilldia]

Hello Oliver, I work at this time with a S-Function for Arduino integration too. I try to integrate EtherCAT with a Arduino EasyCAT Shield in Simulink. It's works fine with the Arduino Due. But there are Problems with the Due in the SPI Libary. What SPI libary you used for your Project? Maybe you have a better one than me.

Thanks a lot.

[Alberto Mora]

Dear Oliver, how did you solve the problem of use LDC1101 with Arduino? Can you share your library? That can help me a lot. Thanks, Alberto.