1 files changed, 199 insertions, 0 deletions
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;
+}