Usable mfrc522 code.

Not as async as possible, and definately needs a future revisit. But
works for now, with acceptable delays, if the newly introduced
tocard_retries parameter of class MFRC522 is used and set to a
reasonable low value.

software/src/mfrc522/main.py

@@ -1,35 +1,65 @@
-from mfrc522 import MFRC522
-import asyncio
-
-
-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:
-    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:
-                return uid
-
-        await asyncio.sleep_ms(poll_interval_ms)
-
-
-def main():
-    reader = MFRC522(spi_id=1, sck=10, miso=12, mosi=11, cs=13, rst=9)
-
-    print("")
-    print("Please place card on reader")
-    print("")
-
-    uid = asyncio.run(get_tag_uid(reader))
-    print(f"Found tag with uid {uid_to_string(uid)}")
-
-
-if __name__ == "__main__":
-    main()
+from mfrc522 import MFRC522
+import asyncio
+import time
+
+delay_sum = 0
+delay_count = 0
+max_delay = 0
+
+
+async def latency_test():
+    global delay_sum
+    global delay_count
+    global max_delay
+    global min_delay
+    min_delay = 0xffffffff
+    await asyncio.sleep_ms(1)
+    while True:
+        for _ in range(2000):
+            before = time.ticks_us()
+            await asyncio.sleep(0)
+            after = time.ticks_us()
+            delay = after - before
+            delay_sum += delay
+            delay_count += 1
+            if delay > max_delay:
+                max_delay = delay
+            if delay < min_delay:
+                min_delay = delay
+            await asyncio.sleep_ms(1)
+        print(f"delay (min / max / avg) [µs]: ({min_delay} / {max_delay} / {delay/delay_sum})")
+
+
+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:
+    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)}")
+
+        await asyncio.sleep_ms(poll_interval_ms)
+
+
+def main():
+    reader = MFRC522(spi_id=1, sck=10, miso=12, mosi=11, cs=13, rst=9, tocard_retries=5)
+
+    print("")
+    print("Please place card on reader")
+    print("")
+
+    asyncio.create_task(get_tag_uid(reader))
+    asyncio.create_task(latency_test())
+
+    asyncio.get_event_loop().run_forever()
+
+
+if __name__ == "__main__":
+    main()