Introduce an MCU driver

Introduce an MCU driver, with a few convenience methods to disable JTAG or clock
division. Both of these were re-implemented by various hardware plugins on their
own, this collapses them into a common implementation.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/kaleidoscope/driver/MCU.h

@@ -0,0 +1,59 @@
+/* -*- mode: c++ -*-
+ * kaleidoscope::driver::mcu -- Various MCU drivers
+ * Copyright (C) 2019  Keyboard.io, Inc
+ *
+ * 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, version 3.
+ *
+ * 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/>.
+ */
+
+#pragma once
+
+namespace kaleidoscope {
+namespace driver {
+namespace mcu {
+
+class ATMega32U4 {
+ public:
+  ATMega32U4() {}
+
+  static inline void disableJTAG() {
+    /* These two lines here are the result of many hours spent chasing ghosts.
+     * These are great lines, and we love them dearly, for they make a set of
+     * pins that would otherwise be reserved for JTAG accessible from the
+     * firmware.
+     *
+     * Most AVR chips that get put into keyboards have the JTAG port disabled in
+     * fuses, but some do not. When they're used for JTAG, then no matter what
+     * we do in the firmware, they will not be affected. So in case JTAG is not
+     * disabled in fuses, we want to do that in the firmware. Luckily for us,
+     * that's doable, we just have to write the JTD bit into MCUCR twice within
+     * four cycles. These two lines do just that.
+     *
+     * For more information, see the ATMega16U4/ATMega32U4 datasheet, the
+     * following sections:
+     *  - 2.2.7 (PIN Descriptions; PIN F)
+     *  - 7.8.7 (On-chip Debug System)
+     *  - 26.5.1 (MCU Control Register – MCUCR)
+     */
+    MCUCR |= (1 << JTD);
+    MCUCR |= (1 << JTD);
+  }
+
+  static inline void disableClockDivision() {
+    CLKPR = (1 << CLKPCE);
+    CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
+  }
+};
+
+}
+}
+}

src/kaleidoscope/hardware/ATMegaKeyboard.h

@@ -40,6 +40,7 @@ struct cRGB {
 #endif
 
 #include "kaleidoscope/Hardware.h"
+#include "kaleidoscope/driver/MCU.h"
 
 #define ROW_PIN_LIST(...)  __VA_ARGS__
 #define COL_PIN_LIST(...)  __VA_ARGS__
@@ -92,6 +93,9 @@ class ATMegaKeyboard : public kaleidoscope::Hardware {
 
   static bool do_scan_;
 
+ protected:
+  kaleidoscope::driver::mcu::ATMega32U4 mcu_;
+
  private:
 
   uint16_t readCols();

src/kaleidoscope/hardware/kbdfans/KBD4x.h

@@ -34,30 +34,8 @@ namespace kbdfans {
 class KBD4x: public kaleidoscope::hardware::ATMegaKeyboard {
  public:
   KBD4x(void) {
-    /* These two lines here are the result of many hours spent chasing ghosts.
-     * These are great lines, and we love them dearly, for they make a set of
-     * pins that would otherwise be reserved for JTAG accessible from the
-     * firmware.
-     *
-     * Most AVR chips that get put into keyboards have the JTAG port disabled in
-     * fuses, but some do not. When they're used for JTAG, then no matter what
-     * we do in the firmware, they will not be affected. So in case JTAG is not
-     * disabled in fuses, we want to do that in the firmware. Luckily for us,
-     * that's doable, we just have to write the JTD bit into MCUCR twice within
-     * four cycles. These two lines do just that.
-     *
-     * For more information, see the ATMega16U4/ATMega32U4 datasheet, the
-     * following sections:
-     *  - 2.2.7 (PIN Descriptions; PIN F)
-     *  - 7.8.7 (On-chip Debug System)
-     *  - 26.5.1 (MCU Control Register – MCUCR)
-     */
-    MCUCR |= (1 << JTD);
-    MCUCR |= (1 << JTD);
-
-    // Disable Clock division
-    CLKPR = (1 << CLKPCE);
-    CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
+    mcu_.disableJTAG();
+    mcu_.disableClockDivision();
   }
 
   ATMEGA_KEYBOARD_CONFIG(

src/kaleidoscope/hardware/softhruf/Splitography.h

@@ -41,26 +41,7 @@ namespace softhruf {
 class Splitography: public kaleidoscope::hardware::ATMegaKeyboard {
  public:
   Splitography(void) {
-    /* These two lines here are the result of many hours spent chasing ghosts.
-     * These are great lines, and we love them dearly, for they make a set of
-     * pins that would otherwise be reserved for JTAG accessible from the
-     * firmware.
-     *
-     * Most AVR chips that get put into keyboards have the JTAG port disabled in
-     * fuses, but some do not. When they're used for JTAG, then no matter what
-     * we do in the firmware, they will not be affected. So in case JTAG is not
-     * disabled in fuses, we want to do that in the firmware. Luckily for us,
-     * that's doable, we just have to write the JTD bit into MCUCR twice within
-     * four cycles. These two lines do just that.
-     *
-     * For more information, see the ATMega16U4/ATMega32U4 datasheet, the
-     * following sections:
-     *  - 2.2.7 (PIN Descriptions; PIN F)
-     *  - 7.8.7 (On-chip Debug System)
-     *  - 26.5.1 (MCU Control Register – MCUCR)
-     */
-    MCUCR |= (1 << JTD);
-    MCUCR |= (1 << JTD);
+    mcu_.disableJTAG();
   }
 
   ATMEGA_KEYBOARD_CONFIG(