例程讲解-02-usb_vcp usb虚拟串口

# USB VCP 示例.
# 此示例显示如何使用USB VCP类按需将图像发送到PC。
#
# 警告：
# 不应该从IDE或命令行运行此脚本，它应保存为main.py.
# 注意以下注释脚本显示了如何从主机端接收图像。
#
# #!/usr/bin/env python2.7
# 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.setDTR(True) # dsrdtr is ignored on Windows.
# sp.write("snap")
# sp.flush()
# size = struct.unpack('<L', sp.read(4))[0]
# img = sp.read(size)
# sp.close()
# 
# with open("img.jpg", "w") as f:
#     f.write(img)

import sensor, image, time, ustruct
from pyb import USB_VCP

usb = USB_VCP()
sensor.reset()                      # Reset and initialize the sensor.
sensor.set_pixformat(sensor.RGB565) # Set pixel format to RGB565 (or GRAYSCALE)
sensor.set_framesize(sensor.QVGA)   # Set frame size to QVGA (320x240)
sensor.skip_frames(time = 2000)     # Wait for settings take effect.

while(True):
    cmd = usb.recv(4, timeout=5000)
    if (cmd == b'snap'):
        img = sensor.snapshot().compress()
        usb.send(ustruct.pack("<L", img.size()))
        usb.send(img)