DO NOT MERGE: Just a PoC. Web request blocks, but it yields a uid if chip is presented.

software/src/microdot/main.py

@@ -1,6 +1,9 @@
-import rp2
+import asyncio
 import network
 import ubinascii
+import rp2
+
+from mfrc522 import MFRC522
 from microdot import Microdot
 
 rp2.country('DE')
@@ -21,6 +24,35 @@ print(f"   essid: {wlan.config('essid')}")
 print(f" txpower: {wlan.config('txpower')}")
 print(f"ifconfig: {wlan.ifconfig()}")
 
+
+def uid_to_string(uid: list):
+    return '0x' + ''.join(f'{i:02x}' for i in uid)
+
+
+
+async def get_tag_uid(reader: MFRC522, poll_interval_ms: int = 50) -> list:
+    '''
+    The maximum measured delay with poll_interval_ms=50 and a reader with tocard_retries=5 is
+    15.9 ms:
+        delay (min / max / avg) [µs]: (360 / 15945 / 1.892923e-06)
+
+    The maximum measured delay dropped to 11.6 ms by setting tocard_retries=1:
+        delay (min / max / avg) [µs]: (368 / 11696 / 6.204211e-06)
+    '''
+    while True:
+        reader.init()
+
+        # For now we omit the tag type
+        (stat, _) = reader.request(reader.REQIDL)
+        if stat == reader.OK:
+            (stat, uid) = reader.SelectTagSN()
+            if stat == reader.OK:
+                print(f"uid={uid_to_string(uid)}")
+                return uid
+
+        await asyncio.sleep_ms(poll_interval_ms)
+
+
 app = Microdot()
 
 
@@ -35,4 +67,16 @@ async def index(request):
     print(f"  cookies: {request.cookies}")
     return "TonberryPico says 'Hello World!'"
 
+
+@app.route('/nfc')
+async def blafasel(request):
+    print("/nfc")
+
+    reader = MFRC522(spi_id=1, sck=10, miso=12, mosi=11, cs=13, rst=9, tocard_retries=10)
+    task = asyncio.create_task(get_tag_uid(reader))
+
+    uid = await task
+
+    return f"result={uid_to_string(uid)}"
+
 app.run(port=80)