Set MICROBIT_RADIO_MAX_PACKET_SIZE as a configurable value.

inc/MicroBitConfig.h

@@ -273,7 +273,14 @@
 // Set to '1' to enable
 #ifndef MICROBIT_BLE_NORDIC_STYLE_UART
     #define MICROBIT_BLE_NORDIC_STYLE_UART 0
-#endif 
+#endif
+
+// Configure the radio maximum packet size
+// TODO: Update the range here once issue codal-microbit-v2#383 has been resolved
+// https://github.com/lancaster-university/codal-microbit-v2/issues/383
+#ifndef MICROBIT_RADIO_MAX_PACKET_SIZE
+    #define MICROBIT_RADIO_MAX_PACKET_SIZE          32
+#endif
 
 // Versioning options.
 // We use semantic versioning (http://semver.org/) to identify differnet versions of the micro:bit runtime.

inc/MicroBitRadio.h

@@ -76,6 +76,13 @@ namespace codal
 #define MICROBIT_RADIO_MAXIMUM_RX_BUFFERS       4
 #define MICROBIT_RADIO_POWER_LEVELS             8
 
+// Max packet size is configurable, so ensure maximum value is not exceeded
+// TODO: Update this value once issue codal-microbit-v2#383 is resolved
+// https://github.com/lancaster-university/codal-microbit-v2/issues/383
+#if MICROBIT_RADIO_MAX_PACKET_SIZE > 250
+    #error "MICROBIT_RADIO_MAX_PACKET_SIZE cannot be larger than 250 bytes"
+#endif
+
 // Known Protocol Numbers
 #define MICROBIT_RADIO_PROTOCOL_DATAGRAM        1       // A simple, single frame datagram. a little like UDP but with smaller packets. :-)
 #define MICROBIT_RADIO_PROTOCOL_EVENTBUS        2       // Transparent propogation of events from one micro:bit to another.