USB CDC between Matlab and EMbedded C (microcontroller)

Hi to you all,

I want to builld a reliable link over USB between my laptopt (ubuntu 18.04) running Matlab R2019a and a Cortex-M4 microcontroller (LPC4370 on LPC-Link2 evaluation board, I'll call it simply mcu).

It's been a while now I don't seem to be able to get to the point where the comunication is stable and realiable (other post I made on the topic here).

My requirements:

• FSM like behaviour: I write a char (command) to the mcu and it responds in switch-case fashion. Then it goes back to idle, ready for next command.
• Data transfer: I need to test HW performance on A LOT of data I generate in matlab, so I need to bulk-transfer vectors of integers, both to and from the mcu.

On the mcu side I'm using a USB API developed by NXP, called LPOCopen: note that this comes with no documentation other than some examples and the support on NXP forums is 0. (I will attach it to this post, since you need to login to download it). On matlab I use fwrite/fread as described here.

My problem is that I loose synchronization between matlab and mcu: most of the time either fread skips bytes either it hangs on until it reaches TimeOut and gives up.

I'll try to explain my software now.

MCU side:

I started off using an example called usbd_rom_cdc_vcom (The example shows how to us USBD ROM stack to creates a virtual comm port, and I will attach it as well). It initializes the USB in interrupt mode and uses 2 functions:

vcom_bread()

/**
 * @brief	Virtual com port buffered read routine
 * @param	pBuf	: Pointer to buffer where read data should be copied
 * @param	buf_len	: Length of the buffer passed
 * @return	Return number of bytes read.
 */
uint32_t vcom_bread (uint8_t *pBuf, uint32_t buf_len);

and

vcom_write()

/**
 * @brief	Virtual com port write routine
 * @param	pBuf	: Pointer to buffer to be written
 * @param	buf_len	: Length of the buffer passed
 * @return	Number of bytes written
 */
uint32_t vcom_write (uint8_t *pBuf, uint32_t buf_len);

So no need to specify:

• Line temrinators
• Baudrate

I just pass the array I want to send and the size of it (in bytes).

I'll attatch the matlab code I use to initialize the serial_object. Here's the status of the serial object right after initialization:

   Serial Port Object : Serial-/dev/ttyACM2

   Communication Settings 
      Port:               /dev/ttyACM2
      BaudRate:           115200
      Terminator:         'LF'

   Communication State 
      Status:             open
      RecordStatus:       off

   Read/Write State  
      TransferStatus:     idle
      BytesAvailable:     0
      ValuesReceived:     0
      ValuesSent:         0
      

As I mention in my post on stackexchange, my basic signaling is the following:

Matlab:

fwrite(serial_object, K_COEFF,  'int32');
if K_COEFF ~= fread(serial_object, 1, 'int32')
 error('out of sync');
 end
pause(0.0005)

fwrite(serial_object, L_COEFF,  'int32');
 if L_COEFF ~= fread(serial_object, 1, 'int32')
 error('out of sync');
end
pause(0.0005)

MCU:

/*SET K*/
while(!rdCnt)
{rdCnt = vcom_bread(&param_rxBuff, sizeof(int32_t));}
K_COEFF = param_rxBuff;
vcom_write((uint8_t*)&param_rxBuff, sizeof(int32_t));
param_rxBuff = 0;
rdCnt = 0;

/*SET L*/
while(!rdCnt)
{rdCnt = vcom_bread(&param_rxBuff, sizeof(int32_t));}
L_COEFF = param_rxBuff;
vcom_write((uint8_t*)&param_rxBuff, sizeof(int32_t));
param_rxBuff = 0;
rdCnt = 0;

But this is not reliable: I'm not sayng it's completely broken, but this thing is not acting in a repetable way.

Since I have 0 experience on USB and low-level matlab as well I wonder if there's something wrong in my whole approach. Especcially on matlab side.

I didn't even find a good document describing how to interface Matlab and an mcu this way.

[Urmila Rajpurohith]

Are you still facing the issue?