非阻塞pn532标签读取

Question

我计划在我的项目中使用Adafruit PN532 nfc https://www.adafruit.com/product/364突破卡。

有没有办法在python中编写非阻塞代码(使用中断)？如何避免循环，如下面的代码示例所示？

PN532/blob/master/examples/readmifare.py

Answer 1

(关于我的评论.)虽然asyncio的重量稍微轻一些，但threading也有一个事件调用系统，并且目前文档化得更好一些(线程处理的时间要比异步长一些，并且不那么抽象)。据我所知，您希望能够在执行其他任务时从阻塞资源中读取数据。在这种情况下，我们将创建一个线程来等待卡片被读取，同时缓慢地打印一个文本文件到stdout。这只是一个如何做这样的事情的例子。有许多方法可以实现类似的结果。

import binascii
import time
import threading
from collections import deque #use as a fifo queue

queue = deque() #queue to pass information from thread to main process
queue_lock = threading.Lock() #prevent possible issues from 
txt_file = '50_shades_of_grey.txt' #don't ask ;)
running = True

def nfc_reader():
    #copied from adafruit example
    import Adafruit_PN532 as PN532
    CS   = 18
    MOSI = 23
    MISO = 24
    SCLK = 25

    pn532 = PN532.PN532(cs=CS, sclk=SCLK, mosi=MOSI, miso=MISO)
    pn532.begin()
    ic, ver, rev, support = pn532.get_firmware_version()
    print(f'Found PN532 with firmware version: {ver}.{rev}')
    pn532.SAM_configuration()

    # Main loop to detect cards and read a block.
    print('Waiting for MiFare card...')
    while True:
        if not running: #cheap way to kill a thread nicely (cheap ain't pretty)
            return
        #don't bother specifying a timeout, they forgot to support it in the library
        uid = pn532.read_passive_target() 
        # Try again if no card is available.
        if uid is None:
            continue
        print('Found card with UID: 0x{0}'.format(binascii.hexlify(uid)))
        # Authenticate block 4 for reading with default key (0xFFFFFFFFFFFF).
        if not pn532.mifare_classic_authenticate_block(uid, 4, PN532.MIFARE_CMD_AUTH_B,
                                                       [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF]):
            print('Failed to authenticate block 4!')
            continue
        # Read block 4 data.
        data = pn532.mifare_classic_read_block(4)
        if data is None:
            print('Failed to read block 4!')
            continue
        # make sure our queue is free
        with queue_lock:
            # replaced print with deque.append
            queue.append(f'Read block 4: 0x{binascii.hexlify(data[:4])}')
        #optionally emit some sort of signal that data is ready. In our case the main loop will chech periodically on it's own

# Main program
nfc_thread = threading.Thread(target=nfc_reader)
nfc_thread.start()

with open(txt_file, 'r') as f:
    while True: #also cheap, but easy
        if queue: #bool(deque) works like bool(list)
            with queue_lock:
                print("we found a card!")
                print(queue.popleft())
                continue
        try:
            print(next(f)) #otherwise go back to more interesting matters
        except StopIteration:
            running = False
            nfc_thread.join()
            break
        time.sleep(.9) #notice loop time will be less than timeout on nfc read.
                       #  you could put the printing of the *book* into another thread
                       #  and use events to immediately call your return from your 
                       #  nfc reader

Answer 2

以下是我尝试过的基于@Aaron答案的代码

import binascii
import time
import threading
from collections import deque #use as a fifo queue
import RPi.GPIO as GPIO
import Adafruit_PN532 as PN532

queue = deque() #queue to pass information from thread to main process
queue_lock = threading.Lock() #prevent possible issues from 
running = True

def nfc_reader():
    CS   = 18
    MOSI = 23
    MISO = 24
    SCLK = 25

    pn532 = PN532.PN532(cs=CS, sclk=SCLK, mosi=MOSI, miso=MISO)
    pn532.begin()
    ic, ver, rev, support = pn532.get_firmware_version()
    print('Found PN532 with firmware version: {0}.{1}'.format(ver, rev))
    pn532.SAM_configuration()

    while True:
        if not running: #cheap way to kill a thread nicely (cheap ain't pretty)
            return

        uid = pn532.read_passive_target()
        if uid is None:
            continue
        #print('card read')
        message = 'Read card\n{0}'.format(binascii.hexlify(uid))

        # make sure our queue is free
        with queue_lock:
            # replaced print with deque.append
            queue.append(message)
            time.sleep(1)
        #optionally emit some sort of signal that data is ready. In our case the main loop will chech periodically on it's own

# Main program
nfc_thread = threading.Thread(target=nfc_reader)
nfc_thread.start()


while True: #also cheap, but easy
    if queue: #bool(deque) works like bool(list)
        with queue_lock:
            print("we found a card!")
            print(queue.popleft())
            continue
    time.sleep(.9) #notice loop time will be less than timeout on nfc read.
                   #  you could put the printing of the *book* into another thread
                   #  and use events to immediately call your return from your 
                   #  nfc reader