Problem with USB VCP

OpenMV Boards
1

I want to communicate with OpenMV camera via USB. I was using OpenMV H7, and everything worked fine. I replaced the camera with the global shutter module, and updated the firmware. Everything works fine on the IDE, but I can not get usb_vcp.py working.

Since the example usb_vcp.py did not work, I tried the simpler example code from this post to test the communication. I repost the code below:

The main.py on OpenMV camera:

import ustruct
from pyb import USB_VCP

usb = USB_VCP()

while(True):
    try:
        cmd = usb.recv(4, timeout=5000)
        if (cmd == b'snap'):
            usb.send(ustruct.pack("<L", 1234))
    except:
        pass

The corresponding python code on the PC:

import sys, serial, struct

port = '/dev/ttyACM0'
sp = serial.Serial(port, baudrate=115200, 
                   bytesize=serial.EIGHTBITS, 
                   parity=serial.PARITY_NONE, 
                   xonxoff=False, rtscts=False, 
                   stopbits=serial.STOPBITS_ONE, 
                   timeout=None, dsrdtr=True)

sp.write(b"snap")
size = struct.unpack('<L', sp.read(4))[0]
sp.close()
print(size)

It works fine. I get 1234 as expected.

Once I changed the code to

import ustruct
from pyb import USB_VCP
import sensor

usb = USB_VCP()

sensor.reset()
sensor.set_pixformat(sensor.RGB565) 
sensor.set_framesize(sensor.QVGA)
sensor.skip_frames(time=2000)

while(True):
    try:
        cmd = usb.recv(4, timeout=5000)
        if (cmd == b'snap'):
            usb.send(ustruct.pack("<L", 1234))
    except:
        pass

I can only get 1885433459, where I should get 1234 as the previous code.

I am not sure how I should debug this. It would be great if there is some guidance. I appreciate the help in advance.

2

Probably main.py throws an exception here because the GS doesn’t support this format.

3

Thanks for the timely reply! That solves my problem! Thank you so much!

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