Allow NFC pins to be used for other purposes.

ports/nrf/boards/makerdiary_nrf52840_mdk_usb_dongle/mpconfigboard.h

@@ -40,7 +40,3 @@
 #define BOARD_FLASH_SIZE (FLASH_SIZE - 0x4000 - CIRCUITPY_INTERNAL_NVM_SIZE)
 
 #define BOARD_HAS_CRYSTAL 1  // according to the schematic we do
-
-// See https://github.com/adafruit/circuitpython/issues/1300, circuitpython
-// doesn't yet support NFC so just force those pins to be GPIO.
-#define CONFIG_NFCT_PINS_AS_GPIOS

ports/nrf/common-hal/microcontroller/Pin.c

@@ -168,5 +168,15 @@ bool common_hal_mcu_pin_is_free(const mcu_pin_obj_t *pin) {
     }
     #endif
 
+    #ifdef NRF52840
+    // If NFC pins are enabled for NFC, don't allow them to be used for GPIO.
+    if (((NRF_UICR->NFCPINS & UICR_NFCPINS_PROTECT_Msk) ==
+         (UICR_NFCPINS_PROTECT_NFC << UICR_NFCPINS_PROTECT_Pos)) &&
+        (pin->number == 9 || pin->number == 10)) {
+        return false;
+    }
+    #endif
+
     return pin_number_is_free(pin->number);
+
 }

ports/nrf/mpconfigport.mk

@@ -27,3 +27,8 @@ CIRCUITPY_RTC = 0
 
 # frequencyio not yet implemented
 CIRCUITPY_FREQUENCYIO = 0
+
+# CircuitPython doesn't yet support NFC so force the NFC antenna pins to be GPIO.
+# See https://github.com/adafruit/circuitpython/issues/1300
+# Defined here because system_nrf52840.c doesn't #include any of our own include files.
+CFLAGS += -DCONFIG_NFCT_PINS_AS_GPIOS