Snake

7 files changed, 966 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..dee53c5
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+build
+*~
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..d31ff5e
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,37 @@
+cmake_minimum_required(VERSION 2.8.3)
+
+
+SET(BOARD "atmega328p" CACHE STRING "AVR CPU to build for")
+SET(CLOCK "16000000" CACHE STRING "CPU clock")
+
+SET(FLASH_FLAGS "-patmega328p" "-carduino" "-P/dev/ttyUSB0" "-b57600" CACHE STRING "avrdude flags")
+
+
+find_program(AVR_GCC avr-gcc)
+find_program(AVRDUDE avrdude)
+
+SET(CMAKE_SYSTEM_NAME Generic)
+
+
+SET(CMAKE_C_COMPILER ${AVR_GCC})
+
+project(ARDKBD C)
+
+set(CMAKE_MODULE_PATH ${ARDKDB_SOURCE_DIR})
+
+
+add_executable(snake.elf
+  Charliplexing.c
+  kbd.c
+  snake.c
+)
+set_target_properties(snake.elf PROPERTIES
+  COMPILE_FLAGS "-Wall -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Os -mmcu=${BOARD}"
+  LINK_FLAGS "-Wall -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Os -mmcu=${BOARD}"
+  COMPILE_DEFINITIONS "F_CPU=${CLOCK}"
+)
+
+add_custom_command(OUTPUT snake.hex COMMAND ${CMAKE_OBJCOPY} -O ihex -R .eeprom snake.elf snake.hex DEPENDS snake.elf)
+add_custom_target(snake ALL DEPENDS snake.hex)
+
+add_custom_target(flash COMMAND ${AVRDUDE} ${FLASH_FLAGS} -D -Uflash:w:snake.hex:i DEPENDS snake)
diff --git a/Charliplexing.c b/Charliplexing.c
new file mode 100644
index 0000000..13cb248
--- /dev/null
+++ b/Charliplexing.c
@@ -0,0 +1,503 @@
+/*
+  Charliplexing.cpp - Using timer2 with 1ms resolution
+
+  Alex Wenger <a.wenger@gmx.de> http://arduinobuch.wordpress.com/
+  Matt Mets <mahto@cibomahto.com> http://cibomahto.com/
+
+  Timer init code from MsTimer2 - Javier Valencia <javiervalencia80@gmail.com>
+  Misc functions from Benjamin Sonnatg <benjamin@sonntag.fr>
+
+  History:
+    2009-12-30 - V0.0 wrote the first version at 26C3/Berlin
+    2010-01-01 - V0.1 adding misc utility functions
+      (Clear, Vertical,  Horizontal) comment are Doxygen complaints now
+    2010-05-27 - V0.2 add double-buffer mode
+    2010-08-18 - V0.9 Merge brightness and grayscale
+
+  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 <math.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include "Charliplexing.h"
+
+volatile unsigned int LedSign_tcnt2;
+
+
+typedef struct _videoPage {
+    uint8_t pixels[SHADES][48];  // TODO: is 48 right?
+} videoPage;
+
+/* -----------------------------------------------------------------  */
+/** Table for the LED multiplexing cycles
+ * Each frame is made of 24 bytes (for the 24 display cycles)
+ * There are SHADES frames per buffer in grayscale mode (one for each brigtness)
+ * and twice that many to support double-buffered grayscale.
+ */
+videoPage leds[2];
+
+/// Determines whether the display is in single or double buffer mode
+uint8_t displayMode = SINGLE_BUFFER;
+
+/// Flag indicating that the display page should be flipped as soon as the
+/// current frame is displayed
+volatile bool videoFlipPage = false;
+
+/// Pointer to the buffer that is currently being displayed
+videoPage* displayBuffer;
+
+/// Pointer to the buffer that should currently be drawn to
+videoPage* workBuffer;
+
+/// Flag indicating that the timer buffer should be flipped as soon as the
+/// current frame is displayed
+volatile bool videoFlipTimer = false;
+
+
+// Timer counts to display each page for, plus off time
+typedef struct timerInfo {
+    uint8_t counts[SHADES];
+    uint8_t prescaler[SHADES];
+} timerInfo;
+
+// Double buffer the timing information, of course.
+timerInfo* frontTimer;
+timerInfo* backTimer;
+
+timerInfo* tempTimer;
+
+timerInfo timer[2];
+
+// Record a slow and fast prescaler for later use
+typedef struct prescalerInfo {
+    uint8_t relativeSpeed;
+    uint8_t TCCR2;
+} prescalerInfo;
+
+// TODO: Generate these based on processor type and clock speed
+prescalerInfo slowPrescaler = {1, 0x03};
+//prescalerInfo fastPrescaler = {32, 0x01};
+prescalerInfo fastPrescaler = {4, 0x02};
+
+static bool initialized = false;
+
+/// Uncomment to set analog pin 5 high during interrupts, so that an
+/// oscilloscope can be used to measure the processor time taken by it
+//#define MEASURE_ISR_TIME
+//#ifdef MEASURE_ISR_TIME
+//uint8_t statusPIN = 19;
+//#endif
+
+typedef struct LEDPosition {
+    uint8_t high;
+    uint8_t low;
+} LEDPosition;
+
+
+/* -----------------------------------------------------------------  */
+/** Table for LED Position in leds[] ram table
+ */
+
+const LEDPosition ledMap[126] = {
+    {13, 5}, {13, 6}, {13, 7}, {13, 8}, {13, 9}, {13,10}, {13,11}, {13,12},
+    {13, 4}, { 4,13}, {13, 3}, { 3,13}, {13, 2}, { 2,13},
+    {12, 5}, {12, 6}, {12, 7}, {12, 8}, {12, 9}, {12,10}, {12,11}, {12,13},
+    {12, 4}, { 4,12}, {12, 3}, { 3,12}, {12, 2}, { 2,12},
+    {11, 5}, {11, 6}, {11, 7}, {11, 8}, {11, 9}, {11,10}, {11,12}, {11,13},
+    {11, 4}, { 4,11}, {11, 3}, { 3,11}, {11, 2}, { 2,11},
+    {10, 5}, {10, 6}, {10, 7}, {10, 8}, {10, 9}, {10,11}, {10,12}, {10,13},
+    {10, 4}, { 4,10}, {10, 3}, { 3,10}, {10, 2}, { 2,10},
+    { 9, 5}, { 9, 6}, { 9, 7}, { 9, 8}, { 9,10}, { 9,11}, { 9,12}, { 9,13},
+    { 9, 4}, { 4, 9}, { 9, 3}, { 3, 9}, { 9, 2}, { 2, 9},
+    { 8, 5}, { 8, 6}, { 8, 7}, { 8, 9}, { 8,10}, { 8,11}, { 8,12}, { 8,13},
+    { 8, 4}, { 4, 8}, { 8, 3}, { 3, 8}, { 8, 2}, { 2, 8},
+    { 7, 5}, { 7, 6}, { 7, 8}, { 7, 9}, { 7,10}, { 7,11}, { 7,12}, { 7,13},
+    { 7, 4}, { 4, 7}, { 7, 3}, { 3, 7}, { 7, 2}, { 2, 7},
+    { 6, 5}, { 6, 7}, { 6, 8}, { 6, 9}, { 6,10}, { 6,11}, { 6,12}, { 6,13},
+    { 6, 4}, { 4, 6}, { 6, 3}, { 3, 6}, { 6, 2}, { 2, 6},
+    { 5, 6}, { 5, 7}, { 5, 8}, { 5, 9}, { 5,10}, { 5,11}, { 5,12}, { 5,13},
+    { 5, 4}, { 4, 5}, { 5, 3}, { 3, 5}, { 5, 2}, { 2, 5},
+};
+
+
+/* -----------------------------------------------------------------  */
+/** Constructor : Initialize the interrupt code.
+ * should be called in setup();
+ */
+void LedSignInit(uint8_t mode)
+{
+//#ifdef MEASURE_ISR_TIME
+//    pinMode(statusPIN, OUTPUT);
+//    digitalWrite(statusPIN, LOW);
+//#endif
+
+	float prescaler = 0.0;
+
+#if defined (__AVR_ATmega168__) || defined (__AVR_ATmega48__) || defined (__AVR_ATmega88__) || defined (__AVR_ATmega328P__) || (__AVR_ATmega1280__)
+	TIMSK2 &= ~(1<<TOIE2);
+	TCCR2A &= ~((1<<WGM21) | (1<<WGM20));
+	TCCR2B &= ~(1<<WGM22);
+	ASSR &= ~(1<<AS2);
+	TIMSK2 &= ~(1<<OCIE2A);
+
+	if ((F_CPU >= 1000000UL) && (F_CPU <= 16000000UL)) {	// prescaler set to 64
+		TCCR2B |= ((1<<CS21) | (1<<CS20));
+		TCCR2B &= ~(1<<CS22);
+		prescaler = 32.0;
+	} else if (F_CPU < 1000000UL) {	// prescaler set to 8
+		TCCR2B |= (1<<CS21);
+		TCCR2B &= ~((1<<CS22) | (1<<CS20));
+		prescaler = 8.0;
+	} else { // F_CPU > 16Mhz, prescaler set to 128
+		TCCR2B |= (1<<CS22);
+		TCCR2B &= ~((1<<CS21) | (1<<CS20));
+		prescaler = 64.0;
+	}
+#elif defined (__AVR_ATmega8__)
+	TIMSK &= ~(1<<TOIE2);
+	TCCR2 &= ~((1<<WGM21) | (1<<WGM20));
+	TIMSK &= ~(1<<OCIE2);
+	ASSR &= ~(1<<AS2);
+
+	if ((F_CPU >= 1000000UL) && (F_CPU <= 16000000UL)) {	// prescaler set to 64
+		TCCR2 |= (1<<CS22);
+		TCCR2 &= ~((1<<CS21) | (1<<CS20));
+		prescaler = 64.0;
+	} else if (F_CPU < 1000000UL) {	// prescaler set to 8
+		TCCR2 |= (1<<CS21);
+		TCCR2 &= ~((1<<CS22) | (1<<CS20));
+		prescaler = 8.0;
+	} else { // F_CPU > 16Mhz, prescaler set to 128
+		TCCR2 |= ((1<<CS22) && (1<<CS20));
+		TCCR2 &= ~(1<<CS21);
+		prescaler = 128.0;
+	}
+#elif defined (__AVR_ATmega128__)
+	TIMSK &= ~(1<<TOIE2);
+	TCCR2 &= ~((1<<WGM21) | (1<<WGM20));
+	TIMSK &= ~(1<<OCIE2);
+
+	if ((F_CPU >= 1000000UL) && (F_CPU <= 16000000UL)) {	// prescaler set to 64
+		TCCR2 |= ((1<<CS21) | (1<<CS20));
+		TCCR2 &= ~(1<<CS22);
+		prescaler = 64.0;
+	} else if (F_CPU < 1000000UL) {	// prescaler set to 8
+		TCCR2 |= (1<<CS21);
+		TCCR2 &= ~((1<<CS22) | (1<<CS20));
+		prescaler = 8.0;
+	} else { // F_CPU > 16Mhz, prescaler set to 256
+		TCCR2 |= (1<<CS22);
+		TCCR2 &= ~((1<<CS21) | (1<<CS20));
+		prescaler = 256.0;
+	}
+#endif
+
+	LedSign_tcnt2 = 256 - (int)((float)F_CPU * 0.0005 / prescaler);
+
+    // Record whether we are in single or double buffer mode
+    displayMode = mode;
+    videoFlipPage = false;
+
+    // Point the display buffer to the first physical buffer
+    displayBuffer = &leds[0];
+
+    // If we are in single buffered mode, point the work buffer
+    // at the same physical buffer as the display buffer.  Otherwise,
+    // point it at the second physical buffer.
+    if( displayMode & DOUBLE_BUFFER ) {
+        workBuffer = &leds[1];
+    }
+    else {
+        workBuffer = displayBuffer;
+    }
+
+    // Set up the timer buffering
+    frontTimer = &timer[0];
+    backTimer = &timer[1];
+
+    videoFlipTimer = false;
+    LedSignSetBrightness(127);
+
+    // Clear the buffer and display it
+    LedSignClear(0);
+    LedSignFlip(false);
+
+    // Then start the display
+	TCNT2 = LedSign_tcnt2;
+#if defined (__AVR_ATmega168__) || defined (__AVR_ATmega48__) || defined (__AVR_ATmega88__) || defined (__AVR_ATmega328P__) || (__AVR_ATmega1280__)
+	TIMSK2 |= (1<<TOIE2);
+#elif defined (__AVR_ATmega128__) || defined (__AVR_ATmega8__)
+	TIMSK |= (1<<TOIE2);
+#endif
+
+    // If we are in double-buffer mode, wait until the display flips before we
+    // return
+    if (displayMode & DOUBLE_BUFFER)
+    {
+        while (videoFlipPage) {
+            _delay_ms(1);
+        }
+    }
+
+    initialized = true;
+}
+
+
+/* -----------------------------------------------------------------  */
+/** Signal that the front and back buffers should be flipped
+ * @param blocking if true : wait for flip before returning, if false :
+ *                 return immediately.
+ */
+void LedSignFlip(bool blocking)
+{
+    if (displayMode & DOUBLE_BUFFER)
+    {
+        // Just set the flip flag, the buffer will flip between redraws
+        videoFlipPage = true;
+
+        // If we are blocking, sit here until the page flips.
+        while (blocking && videoFlipPage) {
+            _delay_ms(1);
+        }
+    }
+}
+
+
+/* -----------------------------------------------------------------  */
+/** Clear the screen completely
+ * @param set if 1 : make all led ON, if not set or 0 : make all led OFF
+ */
+void LedSignClear(int set) {
+    int x, y;
+    for(x=0;x<14;x++)
+        for(y=0;y<9;y++)
+            LedSignSet(x,y,set);
+}
+
+
+/* -----------------------------------------------------------------  */
+/** Clear an horizontal line completely
+ * @param y is the y coordinate of the line to clear/light [0-8]
+ * @param set if 1 : make all led ON, if not set or 0 : make all led OFF
+ */
+void LedSignHorizontal(int y, int set) {
+    int x;
+    for(x=0;x<14;x++)
+        LedSignSet(x,y,set);
+}
+
+
+/* -----------------------------------------------------------------  */
+/** Clear a vertical line completely
+ * @param x is the x coordinate of the line to clear/light [0-13]
+ * @param set if 1 : make all led ON, if not set or 0 : make all led OFF
+ */
+void LedSignVertical(int x, int set) {
+    int y;
+    for(y=0;y<9;y++)
+        LedSignSet(x,y,set);
+}
+
+
+/* -----------------------------------------------------------------  */
+/** Set : switch on and off the leds. All the position #for char in frameString:
+ * calculations are done here, so we don't need to do in the
+ * interrupt code
+ */
+void LedSignSet(uint8_t x, uint8_t y, uint8_t c)
+{
+    uint8_t pin_high = ledMap[x+y*14].high;
+    uint8_t pin_low  = ledMap[x+y*14].low;
+    // pin_low is directly the address in the led array (minus 2 because the
+    // first two bytes are used for RS232 communication), but
+    // as it is a two byte array we need to check pin_high also.
+    // If pin_high is bigger than 8 address has to be increased by one
+
+    uint8_t bufferNum = (pin_low-2)*2 + (pin_high / 8) + ((pin_high > 7)?24:0);
+    uint8_t work = _BV(pin_high & 0x07);
+
+    // If we aren't in grayscale mode, just map any pin brightness to max
+    if (c > 0 && !(displayMode & GRAYSCALE)) {
+        c = SHADES-1;
+    }
+
+    int i;
+    for (i = 0; i < SHADES-1; i++) {
+        if( c > i ) {
+            workBuffer->pixels[i][bufferNum] |= work;   // ON
+        }
+        else {
+            workBuffer->pixels[i][bufferNum] &= ~work;   // OFF
+        }
+    }
+}
+
+
+/* Set the overall brightness of the screen
+ * @param brightness LED brightness, from 0 (off) to 127 (full on)
+ */
+
+void LedSignSetBrightness(uint8_t brightness)
+{
+    // An exponential fit seems to approximate a (perceived) linear scale
+    float brightnessPercent = ((float)brightness / 127)*((float)brightness / 127);
+    uint8_t difference = 0;
+
+    /*   ---- This needs review! Please review. -- thilo  */
+    // set up page counts
+    // TODO: make SHADES a function parameter. This would require some refactoring.
+    int start = 15;
+    int max = 255;
+    float scale = 1.5;
+    float delta = pow( max - start , 1.0 / scale) / (SHADES - 1);
+    uint8_t pageCounts[SHADES];
+
+    pageCounts[0] = max - start;
+    uint8_t i;
+    for (i=1; i<SHADES; i++) {
+        pageCounts[i] = max - ( pow( i * delta, scale ) + start );
+    }
+    //Serial.end();
+
+    if (! initialized) {
+       // set front timer defaults
+        int i;
+        for (i = 0; i < SHADES; i++) {
+            frontTimer->counts[i] = pageCounts[i];
+            // TODO: Generate this dynamically
+            frontTimer->prescaler[i] = slowPrescaler.TCCR2;
+        }
+    }
+
+    // Wait until the previous brightness request goes through
+    while( videoFlipTimer ) {
+        _delay_ms(1);
+    }
+
+    // Compute on time for each of the pages
+    // Use the fast timer; slow timer is only useful for < 3 shades.
+    for (i = 0; i < SHADES - 1; i++) {
+        uint8_t interval = 255 - pageCounts[i];
+
+        backTimer->counts[i] = 255 -    brightnessPercent
+                                      * interval
+                                      * fastPrescaler.relativeSpeed;
+        backTimer->prescaler[i] = fastPrescaler.TCCR2;
+        difference += backTimer->counts[i] - pageCounts[i];
+    }
+
+    // Compute off time
+    backTimer->counts[SHADES - 1] = 255 - difference;
+    backTimer->prescaler[SHADES - 1] = slowPrescaler.TCCR2;
+
+    /*   ---- End of "This needs review! Please review." -- thilo  */
+
+    // Have the ISR update the timer registers next run
+    videoFlipTimer = true;
+}
+
+
+/* -----------------------------------------------------------------  */
+/** The Interrupt code goes here !
+ */
+ISR(TIMER2_OVF_vect) {
+        DDRD  = 0x0;
+        DDRB  = 0x0;
+	//#ifdef MEASURE_ISR_TIME
+	//    digitalWrite(statusPIN, HIGH);
+	//#endif
+
+    // For each cycle, we have potential SHADES pages to display.
+    // Once every page has been displayed, then we move on to the next
+    // cycle.
+
+    // 24 Cycles of Matrix
+    static uint8_t cycle = 0;
+
+    // SHADES pages to display
+    static uint8_t page = 0;
+
+    TCCR2B = frontTimer->prescaler[page];
+    TCNT2 = frontTimer->counts[page];
+
+    if ( page < SHADES - 1) {
+
+        if (cycle < 6) {
+            DDRD  = _BV(cycle+2) | displayBuffer->pixels[page][cycle*2];
+            PORTD =            displayBuffer->pixels[page][cycle*2];
+
+            DDRB  =            displayBuffer->pixels[page][cycle*2+1];
+            PORTB =            displayBuffer->pixels[page][cycle*2+1];
+        } else if (cycle < 12) {
+            DDRD =             displayBuffer->pixels[page][cycle*2];
+            PORTD =            displayBuffer->pixels[page][cycle*2];
+
+            DDRB  = _BV(cycle-6) | displayBuffer->pixels[page][cycle*2+1];
+            PORTB =            displayBuffer->pixels[page][cycle*2+1];
+        } else if (cycle < 18) {
+            DDRD  = _BV(cycle+2-12) | displayBuffer->pixels[page][cycle*2];
+            PORTD =            displayBuffer->pixels[page][cycle*2];
+
+            DDRB  =            displayBuffer->pixels[page][cycle*2+1];
+            PORTB =            displayBuffer->pixels[page][cycle*2+1];
+        } else {
+            DDRD =             displayBuffer->pixels[page][cycle*2];
+            PORTD =            displayBuffer->pixels[page][cycle*2];
+
+            DDRB  = _BV(cycle-6-12) | displayBuffer->pixels[page][cycle*2+1];
+            PORTB =            displayBuffer->pixels[page][cycle*2+1];
+        }
+    }
+    else {
+        // Turn everything off
+        DDRD  = 0x0;
+        DDRB  = 0x0;
+    }
+
+    page++;
+
+    if (page >= SHADES) {
+        page = 0;
+        cycle++;
+    }
+
+    if (cycle > 24) {
+        cycle = 0;
+
+        // If the page should be flipped, do it here.
+        if (videoFlipPage && (displayMode & DOUBLE_BUFFER))
+        {
+            // TODO: is this an atomic operation?
+            videoFlipPage = false;
+
+            videoPage* temp = displayBuffer;
+            displayBuffer = workBuffer;
+            workBuffer = temp;
+        }
+
+        if (videoFlipTimer) {
+            videoFlipTimer = false;
+
+            tempTimer = frontTimer;
+            frontTimer = backTimer;
+            backTimer = tempTimer;
+        }
+    }
+
+    //#ifdef MEASURE_ISR_TIME
+    //    digitalWrite(statusPIN, LOW);
+    //#endif
+}
diff --git a/Charliplexing.h b/Charliplexing.h
new file mode 100644
index 0000000..3a912d6
--- /dev/null
+++ b/Charliplexing.h
@@ -0,0 +1,33 @@
+/*
+  Charliplexing.h - Library for controlling the charliplexed led board
+  from JimmiePRodgers.com
+  Created by Alex Wenger, December 30, 2009.
+  Modified by Matt Mets, May 28, 2010.
+  Released into the public domain.
+*/
+
+#ifndef Charliplexing_h
+#define Charliplexing_h
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#define SINGLE_BUFFER 0
+#define DOUBLE_BUFFER 1
+#define GRAYSCALE     2
+
+#define DISPLAY_COLS 14     // Number of columns in the display
+#define DISPLAY_ROWS 9      // Number of rows in the display
+#define SHADES 8 // Number of distinct shades to display, including black, i.e. OFF
+
+extern volatile unsigned int LedSign_tcnt2;
+
+void LedSignInit(uint8_t mode);
+void LedSignSet(uint8_t x, uint8_t y, uint8_t c);
+void LedSignSetBrightness(uint8_t brightness);
+void LedSignFlip(bool blocking);
+void LedSignClear(int set);
+void LedSignHorizontal(int y, int set);
+void LedSignVertical(int x, int set);
+
+#endif
diff --git a/kbd.c b/kbd.c
new file mode 100644
index 0000000..e3342e9
--- /dev/null
+++ b/kbd.c
@@ -0,0 +1,167 @@
+#include "kbd.h"
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+
+#include <stdbool.h>
+#include <stdint.h>
+
+
+static volatile int8_t kbd_state = 0;
+
+static volatile uint8_t kbd_input = 0;
+static volatile uint8_t kbd_output = 0;
+static volatile uint8_t kbd_flags = 0;
+
+
+static volatile uint8_t ts = 10;
+
+
+static inline bool kbd_data() {
+	return (PINC & (1 << 0));
+}
+
+static inline bool kbd_clock() {
+	return (PINC & (1 << 1));
+}
+
+
+static inline void kbd_clock_down() {
+	DDRC |= 0x02;
+	PORTC &= ~0x02;
+}
+
+static inline void kbd_clock_in() {
+	DDRC &= ~0x02;
+	PORTC |= 0x02;
+}
+
+static inline void kbd_data_set(bool state) {
+	if (state)
+		PORTC |= 0x01;
+	else
+		PORTC &= ~0x01;
+}
+
+static inline void kbd_data_out() {
+	DDRC |= 0x01;
+}
+
+static inline void kbd_data_in() {
+	DDRC &= ~0x01;
+	PORTC |= 0x01;
+}
+
+
+static inline void kbd_wait() {
+	while (kbd_state) {}
+}
+
+
+ISR(PCINT1_vect) {
+	if (kbd_clock())
+		return;
+
+	if (kbd_state < 0) {
+		if (kbd_state >= -8) {
+			kbd_data_set(kbd_output & _BV(-1-kbd_state));
+		}
+		else if (kbd_state == -9) {
+			kbd_data_set(!(__builtin_popcount(kbd_output) & 1));
+		}
+		else if (kbd_state == -10) {
+			kbd_data_in();
+		}
+		else {
+			kbd_state = 0;
+			return;
+		}
+
+		kbd_state--;
+		return;
+	}
+
+	bool data = kbd_data();
+
+	if (kbd_state == 0) {
+		if (!data) { /* start bit */
+			kbd_input = 0;
+			kbd_state++;
+		}
+
+		return;
+	}
+
+	if (kbd_state <= 8) {
+		if (data)
+			kbd_input |= _BV(kbd_state-1);
+		kbd_state++;
+		return;
+	}
+
+	if (kbd_state == 9) {
+		if ((__builtin_popcount(kbd_input) & 1) == data)
+			kbd_flags |= KBD_FLAG_ERROR;
+
+		kbd_state++;
+		return;
+	}
+
+	kbd_state = 0;
+
+	if (kbd_flags & KBD_FLAG_ERROR) {
+		/* Retry */
+		return;
+	}
+
+	if (kbd_input == 0xe0) {
+		kbd_flags |= KBD_FLAG_EXT;
+		return;
+	}
+
+	if (kbd_input == 0xf0) {
+		kbd_flags |= KBD_FLAG_BREAK;
+		return;
+	}
+
+	uint16_t code = kbd_input;
+	if (kbd_flags & KBD_FLAG_EXT)
+		code |= 0xe000;
+
+	kbd_handle(code, !(kbd_flags & KBD_FLAG_BREAK));
+
+	kbd_flags = 0;
+}
+
+
+void kbd_send(uint8_t command) {
+	kbd_wait();
+
+	kbd_clock_down();
+	_delay_us(100);
+
+	kbd_data_out();
+	kbd_data_set(false);
+	_delay_us(10);
+
+	kbd_clock_in();
+
+	kbd_output = command;
+	kbd_state = -1;
+
+	kbd_wait();
+
+	/* wait for ack */
+	while (!kbd_state) {}
+
+	kbd_wait();
+}
+
+void kbd_init(void) {
+	DDRC  &= ~0x03;
+	PORTC |= 0x03;
+
+	PCMSK1 = (1 << PCINT9);
+	PCICR = (1 << PCIE1);
+}
diff --git a/kbd.h b/kbd.h
new file mode 100644
index 0000000..7ad3a21
--- /dev/null
+++ b/kbd.h
@@ -0,0 +1,25 @@
+#ifndef _AVR_KBD_H_
+#define _AVR_KBD_H_
+
+#include <avr/io.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#define KBD_FLAG_ERROR  (_BV(0))
+#define KBD_FLAG_BREAK  (_BV(1))
+#define KBD_FLAG_EXT    (_BV(2))
+
+#define KBD_CODE_UP     0xe075
+#define KBD_CODE_LEFT   0xe06b
+#define KBD_CODE_DOWN   0xe072
+#define KBD_CODE_RIGHT  0xe074
+
+#define KBD_CMD_RESET   0xff
+
+
+void kbd_handle(uint16_t code, bool make);
+
+void kbd_send(uint8_t command);
+void kbd_init(void);
+
+#endif /* _AVR_KBD_H_ */
diff --git a/snake.c b/snake.c
new file mode 100644
index 0000000..19336eb
--- /dev/null
+++ b/snake.c
@@ -0,0 +1,199 @@
+#include "Charliplexing.h"
+#include "kbd.h"
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+
+
+typedef struct _point_t {
+  uint8_t x, y;
+} point_t;
+
+
+typedef enum _dir_t {
+	NORTH = 0,
+	WEST,
+	SOUTH,
+	EAST
+} dir_t;
+
+
+static volatile uint8_t dir;
+
+static point_t tail = {7, 4};
+
+#define HISTORY_MAX 128
+
+static uint8_t history[HISTORY_MAX >> 2];
+static uint8_t history_len = 0;
+static uint8_t history_pos = 0;
+
+static point_t q;
+
+static uint16_t rand(void) {
+	static uint16_t lfsr = 0xace1;
+	unsigned bit;
+
+	/* taps: 16 14 13 11; feedback polynomial: x^16 + x^14 + x^13 + x^11 + 1 */
+	bit  = ((lfsr >> 0) ^ (lfsr >> 2) ^ (lfsr >> 3) ^ (lfsr >> 5)) & 1;
+	lfsr =  (lfsr >> 1) | (bit << 15);
+
+	return lfsr;
+}
+
+static void rand_q(void) {
+	q.x = rand() % 14;
+	q.y = rand() % 9;
+}
+
+static inline uint8_t rev(uint8_t d) {
+	return d ^ 2;
+}
+
+static inline bool points_equal(const point_t *p1, const point_t *p2) {
+	return p1->x == p2->x && p1->y == p2->y;
+}
+
+static void move(uint8_t d, bool grow) {
+	uint8_t p = (history_pos+history_len) % HISTORY_MAX;
+
+	uint8_t n = p >> 2, shift = (p & 3) << 1;
+
+	history[n] &= ~(3 << shift);
+	history[n] |= d << shift;
+
+	if (grow)
+		history_len++;
+	else
+		history_pos = (history_pos+1) % HISTORY_MAX;
+}
+
+static uint8_t get_dir(uint8_t i) {
+	uint8_t p = (history_pos+i) % HISTORY_MAX;
+
+	uint8_t n = p >> 2, shift = (p & 3) << 1;
+
+	return (history[n] >> shift) & 3;
+}
+
+static void reset(void) {
+	rand_q();
+
+	dir = EAST;
+	tail = (point_t){7, 4};
+	history_len = 0;
+	history_pos = 0;
+
+	unsigned i;
+	for (i = 0; i < 2; i++)
+		move(EAST, true);
+}
+
+void kbd_handle(uint16_t code, bool make) {
+	if (!make)
+		return;
+
+	switch(code) {
+	case KBD_CODE_UP:
+		dir = NORTH;
+		break;
+
+	case KBD_CODE_LEFT:
+		dir = WEST;
+		break;
+
+	case KBD_CODE_DOWN:
+		dir = SOUTH;
+		break;
+
+	case KBD_CODE_RIGHT:
+		dir = EAST;
+	}
+}
+
+static void go(point_t *point, uint8_t d) {
+	switch (d) {
+	case NORTH:
+		point->y = (point->y+8)%9;
+		break;
+	case WEST:
+		point->x = (point->x+13)%14;
+		break;
+	case SOUTH:
+		point->y = (point->y+1)%9;
+		break;
+	case EAST:
+		point->x = (point->x+1)%14;
+	}
+}
+
+static bool point_used(const point_t *p, bool head) {
+	point_t pt = tail;
+
+	unsigned i;
+	for (i = 0; i < history_len - (head ? 0 : 1); i++) {
+		go(&pt, get_dir(i));
+
+		if (points_equal(&pt, p))
+			return true;
+	}
+
+	return false;
+}
+
+static void step(void) {
+	uint8_t d = dir;
+
+	LedSignSet(tail.x, tail.y, 0);
+
+	int i;
+	point_t pt = tail;
+
+	LedSignSet(pt.x, pt.y, 0);
+
+	for (i = 0; i < history_len; i++) {
+		go(&pt, get_dir(i));
+		LedSignSet(pt.x, pt.y, 2);
+	}
+
+	go(&pt, d);
+	LedSignSet(pt.x, pt.y, 3);
+
+	if (point_used(&pt, true)) {
+		while(true) {}
+	}
+
+	if (points_equal(&pt, &q)) {
+		rand_q();
+		move(d, true);
+	}
+	else {
+		go(&tail, get_dir(0));
+		move(d, false);
+	}
+
+	if (point_used(&pt, false)) {
+		while(true) {}
+	}
+
+	LedSignSet(q.x, q.y, 7);
+}
+
+int main() {
+	LedSignInit(GRAYSCALE);
+	kbd_init();
+
+	reset();
+
+	sei();
+
+	kbd_send(KBD_CMD_RESET);
+
+	while(true) {
+		step();
+		_delay_ms(100);
+	}
+
+	return 0;
+}