问：用 Python 写一个字符串到 HID 设备？

编程问答 2022-05-30

问题描述

我有一个带有 2 个天线（ant1、ant2）的 RFID 阅读器，它连接到一个 RPi4（树莓派）上，它的作用就像一个 HID USB 键盘。在这些帖子之后，我设法读取了它的天线输出：

  1. How can I get a String from HID device in Python with evdev?
  2. Send HID report with PyUSB
  3. USB HID device only firing 1 event

python3 中使用 evdev 模块连续读取天线的代码如下：

#!/usr/bin/python3 python3
# -*- coding: utf-8 -*-

# This script reads the output from HID device rfid scanner
# Make sure evdev is installed or install it with: pip3 install evdev.
# The Kernel on the Pi creates an input device which resides in /dev/input/.
# You can find out the names and other attributes of different devices using:
# cat /proc/bus/input/devices

import sys
import inspect
import serial
import time
import random
import csv

import evdev
from evdev import InputDevice,categorize,ecodes as e,list_devices

device = evdev.InputDevice('/dev/input/event1')     # check the event id first with cat 

# reserve the device or maybe not
device.grab()

# return the current line number
def lineno():
    return inspect.currentframe().f_back.f_lineno

CODE_MAP_CHAR = {
    'KEY_MINUS': "-",'KEY_SPACE': " ",'KEY_U': "U",'KEY_W': "W",'KEY_BACKSLASH': "\\",'KEY_GRAVE': "`",'KEY_NUMERIC_STAR': "*",'KEY_NUMERIC_3': "3",'KEY_NUMERIC_2': "2",'KEY_NUMERIC_5': "5",'KEY_NUMERIC_4': "4",'KEY_NUMERIC_7': "7",'KEY_NUMERIC_6': "6",'KEY_NUMERIC_9': "9",'KEY_NUMERIC_8': "8",'KEY_NUMERIC_1': "1",'KEY_NUMERIC_0': "0",'KEY_E': "E",'KEY_D': "D",'KEY_G': "G",'KEY_F': "F",'KEY_A': "A",'KEY_C': "C",'KEY_B': "B",'KEY_M': "M",'KEY_L': "L",'KEY_O': "O",'KEY_N': "N",'KEY_I': "I",'KEY_H': "H",'KEY_K': "K",'KEY_J': "J",'KEY_Q': "Q",'KEY_P': "P",'KEY_S': "S",'KEY_X': "X",'KEY_Z': "Z",'KEY_q': "q",'KEY_w': "w",'KEY_e': "e",'KEY_r': "r",'KEY_t': "t",'KEY_z': "z",'KEY_u': "u",'KEY_i': "i",'KEY_o': "o",'KEY_p': "p",'KEY_a': "a",'KEY_s': "s",'KEY_d': "d",'KEY_f': "f",'KEY_g': "g",'KEY_h': "h",'KEY_j': "k",'KEY_l': "l",'KEY_y': "y",'KEY_x': "x",'KEY_c': "c",'KEY_v': "v",'KEY_b': "b",'KEY_n': "n",'KEY_m': "m",'KEY_KP4': "4",'KEY_KP5': "5",'KEY_KP6': "6",'KEY_KP7': "7",'KEY_KP0': "0",'KEY_KP1': "1",'KEY_KP2': "2",'KEY_KP3': "3",'KEY_KP8': "8",'KEY_KP9': "9",'KEY_5': "5",'KEY_4': "4",'KEY_7': "7",'KEY_6': "6",'KEY_1': "1",'KEY_0': "0",'KEY_3': "3",'KEY_2': "2",'KEY_9': "9",'KEY_8': "8",'KEY_LEFTBRACE': "[",'KEY_RIGHTBRACE': "]",'KEY_COMMA': ",",'KEY_EQUAL': "=",'KEY_SEMICOLON': ";",'KEY_APOSTROPHE': "'",'KEY_T': "T",'KEY_V': "V",'KEY_R': "R",'KEY_Y': "Y",'KEY_TAB': "\t",'KEY_DOT': ".",'KEY_SLASH': "/",}

scancodes = {
    # Scancode: ASCIICode
    0: None,1: u'ESC',2: u'1',3: u'2',4: u'3',5: u'4',6: u'5',7: u'6',8: u'7',9: u'8',10: u'9',11: u'0',12: u'-',13: u'=',14: u'BKSP',15: u'TAB',16: u'Q',17: u'W',18: u'E',19: u'R',20: u'T',21: u'Y',22: u'U',23: u'I',24: u'O',25: u'P',26: u'[',27: u']',28: u'CRLF',29: u'LCTRL',30: u'A',31: u'S',32: u'D',33: u'F',34: u'G',35: u'H',36: u'J',37: u'K',38: u'L',39: u';',40: u'"',41: u'`',42: u'LSHFT',43: u'\\',44: u'Z',45: u'X',46: u'C',47: u'V',48: u'B',49: u'N',50: u'M',51: u',',52: u'.',53: u'/',54: u'RSHFT',56: u'LALT',100: u'RALT'
}

def parse_key_to_char(val):
    return CODE_MAP_CHAR[val] if val in CODE_MAP_CHAR else ""

if __name__ == "__main__":
        
    event_id = 1    # set event id for lcd
    exclusive_access = 1    # grant exclusive access

    device = InputDevice('/dev/input/event{}'.format(event_id))
    if int(exclusive_access) == 1:
        device.grab()
        
    obidList = []   # set list for the reply string
    #print(lineno(),"obidList:",obidList)
    
    #get reply
    for event in device.read_loop():
        if event.type == evdev.ecodes.EV_KEY:
            e = categorize(event)
            if e.keystate == e.key_up:
                sys.stdout.write(parse_key_to_char(e.keycode))
                cifra = parse_key_to_char(e.keycode)
                obidList.append(cifra)
                print(lineno(),obidList)
                sys.stdout.flush()
            if e.scancode == 28:
                obidString = "".join(obidList)  # convert the list into a string
                obidString = obidString.strip() # strip of eventual white spaces
                print(lineno(),obidString)
                break

上面代码的输出是：

(py3) pi@raspBerrypi:~/Desktop/python3 $ python obid_read.py 
device /dev/input/event1,name "FEIG ELECTRONIC GmbH OBID RFID-Reader",phys "usb-0000:01:00.0-1.3/input1" 

10004597E7A656780,02204 bag,antenna2: 004597E7A656780,02
208 obidCount: 1
0004597E7A656780,020004597E7A656780,01197 cartridge,antenna1: 004597E7A656780,01
201 obidCount: 2
004597E7A656780,(py3) pi@raspBerrypi:~/Desktop/python3 $ 004597E7A656780,02

为了控制阅读器并能够读取单个天线，我必须向设备发送一个字符串。字符串是十六进制的，需要转换为字节拳：

# strings to send
hex_string_ant1 = "02 00 0A FF B0 01 10 01 EF 14"
hex_string_ant2 = "02 00 0A FF B0 01 10 02 74 26"
byte_string_1 = bytearray.fromhex(hex_string_ant1)
byte_string_2 = bytearray.fromhex(hex_string_ant2)

我已经检查了涵盖 injecting input keys pressing 的 evdev 文档，但看不到如何关联。如何使用 evedev 向设备发送字节字符串？

解决方法

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evdevhidlinuxlinuxpython-3.xraspberry-pi4