add a variant based on the nrf52840-dk but with a RC clock.

Because I was dumb and accidentally ran some code that configured gpio 0
as an output and that was enough to smoke the xtal that was preinstalled
between P0.0 and P0.1.

variants/pca10056-rc-clock/variant.cpp

@@ -0,0 +1,49 @@
+/*
+  Copyright (c) 2014-2015 Arduino LLC.  All right reserved.
+  Copyright (c) 2016 Sandeep Mistry All right reserved.
+  Copyright (c) 2018, Adafruit Industries (adafruit.com)
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the GNU Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include "variant.h"
+#include "wiring_constants.h"
+#include "wiring_digital.h"
+#include "nrf.h"
+
+const uint32_t g_ADigitalPinMap[] =
+{
+  // P0
+  0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 ,
+  8 , 9 , 10, 11, 12, 13, 14, 15,
+  16, 17, 18, 19, 20, 21, 22, 23,
+  24, 25, 26, 27, 28, 29, 30, 31,
+
+  // P1
+  32, 33, 34, 35, 36, 37, 38, 39,
+  40, 41, 42, 43, 44, 45, 46, 47
+};
+
+
+void initVariant()
+{
+  // LED1 & LED2
+  pinMode(PIN_LED1, OUTPUT);
+  ledOff(PIN_LED1);
+
+  pinMode(PIN_LED2, OUTPUT);
+  ledOff(PIN_LED2);;
+}
+