Read USB Camera in Nvidia Jetson TX2 Development Board

camera_usb.py

from PIL import Image
import sys
import os
import pdb
import urllib
from posix_ipc import *
from mmap import *
import subprocess

# Python modules
import mmap
import os
import sys
import hashlib

# 3rd party modules
import posix_ipc


# globals
ipc = {}
ipc['app2py'] = None
ipc['py2app'] = None
ipc['shm_app2py'] = None
ipc['shm_py2app'] = None

# ----- ----- ----- ----- ----- ----- ----- ----- ----- -----
def ipc_init():
    global ipc
    # Semaphore(name, [flags = 0, [mode = 0600, [initial_value = 0]]])
    # Creates a new semaphore or opens an existing one.
    ipc['app2py'] = Semaphore("/ipc_app2py", flags=O_CREAT)
    ipc['py2app'] = Semaphore("/ipc_py2app", flags=O_CREAT)
    # SharedMemory(name, [flags = 0, [mode = 0600, ]]])
    # Creates a new shared memory segment or opens an existing one.
    ipc['shm_app2py'] = SharedMemory("/ipc_shm_app2py", flags=O_CREAT,
        size=SHMEM_BUF_SIZE_BYTES)
    ipc['shm_py2app'] = SharedMemory("/ipc_shm_py2app", flags=O_CREAT,
        size=SHMEM_BUF_SIZE_BYTES)

    # -----  -----  -----
    # spawn the camera server + rendering process   
    subprocess.Popen(['../tegra_mm_jetpack33/samples/12_camera_v4l2_cuda/camera_v4l2_cuda',
        '-d', '/dev/video4'])    


def ipc_pend():
    global ipc

    print("ipc: waiting...")
    # ex) acquire([timeout = None])
    # Waits (conditionally) until the semaphore's value is > 0
    # and then returns, decrementing the semaphore.
    ipc['app2py'].acquire()
    print("ipc: got event!")
    # Read at most n bytes from file descriptor fd.
    # Return a string containing the bytes read.
    data = os.read(ipc['shm_app2py'].fd, 300 * 300 * 5 * 3)
    # Set the current position of file descriptor fd to position pos,
    # modified by how: SEEK_SET or 0 to set the position relative
    os.lseek(ipc['shm_app2py'].fd, 0, os.SEEK_SET)
    img = Image.frombytes('RGB', (1500,300), data)

    return img


def ipc_post(buf):
    global ipc

    print("ipc: posting...")
    os.lseek(ipc['shm_py2app'].fd, 0, os.SEEK_SET)
    os.write(ipc['shm_py2app'].fd, buf)
    os.fsync(ipc['shm_py2app'].fd)
    ipc['py2app'].release()


# ----- ----- ----- ----- ----- ----- ----- ----- ----- -----
def main():
    ipc_init()

    imgs = [None] * 5

    while True:
        image = ipc_pend();

        # Loading and Preprocessing Image
        py2app_response_arr = []
        py2app_response_arr.append(float('nan'))
        ipc_post(bytearray(np.array(py2app_response_arr, dtype=np.float32)))


if __name__ == "__main__":
    main()