Add software spi support for max6675

Marlin/spi.h

@@ -0,0 +1,68 @@
+/**
+ * Marlin 3D Printer Firmware
+ * Copyright (C) 2016 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef __SPI_H__
+#define __SPI_H__
+
+#include <stdint.h>
+#include "softspi.h"
+
+template<uint8_t MisoPin, uint8_t MosiPin, uint8_t SckPin>
+class Spi {
+  static SoftSPI<MisoPin, MosiPin, SckPin> softSpi;
+  public:
+    inline __attribute__((always_inline))
+    static void init() {
+        softSpi.begin();
+    }
+    inline __attribute__((always_inline))
+    static void send(uint8_t data) {
+        softSpi.send(data);
+    }
+    inline __attribute__((always_inline))
+    static uint8_t receive() {
+        return softSpi.receive();
+    }
+};
+
+
+//hardware spi
+template<>
+class Spi<MISO_PIN, MOSI_PIN, SCK_PIN> {
+  public:
+    inline __attribute__((always_inline))
+    static void init() {
+        OUT_WRITE(SCK_PIN, LOW);
+        OUT_WRITE(MOSI_PIN, HIGH);
+        SET_INPUT(MISO_PIN);
+        WRITE(MISO_PIN, HIGH);
+    }
+    inline __attribute__((always_inline))
+    static uint8_t receive() {
+      SPDR = 0;
+      for (;!TEST(SPSR, SPIF););
+      return SPDR;
+    }
+
+};
+
+#endif