Change method for scanning for card from poll, which is OK for USB-co…

…nnected PN532, but causes 100% CPU usage with SPI-connected PN532

brmdoor_nfc_daemon.py

@@ -127,8 +127,10 @@ def run(self):
                     e = threading.Event()
                     e.wait(timeout=0.3)
             except NFCError, e:
-                #this exception happens also when scanUID times out
-                logging.debug("Failed to wait for RFID card: %s", e)
+                #this exception happens also when scanUID finds no cards
+                logging.debug("Failed to find RFID cards in reader's field: %s", e)
+                e = threading.Event()
+                e.wait(timeout=0.2)
             except KeyboardInterrupt:
                 logging.info("Exiting on keyboard interrupt")
                 self.nfc.close()

nfc_smartcard.cpp

@@ -104,19 +104,16 @@ std::string NFCDevice::scanUID() throw(NFCError)
         throw NFCError("NFC device not opened");
     }
 
-    // We release GIL because otherwise it would block other threads. Since this polling is de-facto sleep and
-    // doesn't touch any variables, it works as a language without GIL would.
-    Py_BEGIN_ALLOW_THREADS
-    res = nfc_initiator_poll_target(_nfcDevice, _modulations, _modulationsLen, pollNr, pollPeriod, &nt);
-    Py_END_ALLOW_THREADS
+    /* nfc_initiator_poll_target works fine for USB-connected PN532 (sleeps until card is available or timeout),
+     * but causes 100% CPU usage on SPI-connected PN532
+     */
+    //res = nfc_initiator_poll_target(_nfcDevice, _modulations, _modulationsLen, pollNr, pollPeriod, &nt);
+    res = nfc_initiator_list_passive_targets(_nfcDevice, _modulations[0], &nt, 1);
 
     if (res < 0) {
-        throw NFCError("NFC polling error");
-    }
-
-    // we are not interested in non-ISO-14443A cards
-    if (nt.nm.nmt != NMT_ISO14443A) {
-        return string();
+        throw NFCError("NFC list passive targets error");
+    } else if (res == 0) {
+        throw NFCError("No card in reader's field");
     }
 
     const nfc_iso14443a_info& nai = nt.nti.nai;

nfc_smartcard.h

@@ -99,11 +99,13 @@ class NFCDevice
     virtual ~NFCDevice();
 
     /** 
-     * Poll until a ISO14443A card is in the field and returns its UID.
+     * Read UID of a card in field. If multiple cards are found, return UID of first one.
+     *
+     * If you are polling for cards with this, include some sleep in-between the calls (e.g. 0.1 sec).
      * 
      * @returns binary string containing UID or empty if non-supported card
      *          present in reader field
-     * @throws NFCError if polling failed
+     * @throws NFCError if no cards in reader's field
      */
     std::string scanUID() throw(NFCError);