From b0dda6fda27cc894673b3d96f92660b17d822eea Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Thu, 14 Mar 2013 22:52:04 +0100
Subject: Improve random, allow playing more than one game

---
 kbd.h   |  1 +
 snake.c | 41 +++++++++++++++++++++++++++++------------
 2 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/kbd.h b/kbd.h
index 7ad3a21..0c8566e 100644
--- a/kbd.h
+++ b/kbd.h
@@ -9,6 +9,7 @@
 #define KBD_FLAG_BREAK  (_BV(1))
 #define KBD_FLAG_EXT    (_BV(2))
 
+#define KBD_CODE_SPACE  0x29
 #define KBD_CODE_UP     0xe075
 #define KBD_CODE_LEFT   0xe06b
 #define KBD_CODE_DOWN   0xe072
diff --git a/snake.c b/snake.c
index 19336eb..2b87327 100644
--- a/snake.c
+++ b/snake.c
@@ -4,6 +4,7 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <util/delay.h>
+#include <stdbool.h>
 
 
 typedef struct _point_t {
@@ -20,6 +21,8 @@ typedef enum _dir_t {
 
 
 static volatile uint8_t dir;
+static volatile bool start = false;
+static volatile uint16_t lfsr = 0xace1;
 
 static point_t tail = {7, 4};
 
@@ -32,7 +35,6 @@ 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 */
@@ -42,6 +44,10 @@ static uint16_t rand(void) {
 	return lfsr;
 }
 
+static void rand_mix(uint16_t mix) {
+	lfsr ^= mix;
+}
+
 static void rand_q(void) {
 	q.x = rand() % 14;
 	q.y = rand() % 9;
@@ -78,6 +84,8 @@ static uint8_t get_dir(uint8_t i) {
 }
 
 static void reset(void) {
+	LedSignClear(0);
+
 	rand_q();
 
 	dir = EAST;
@@ -95,6 +103,10 @@ void kbd_handle(uint16_t code, bool make) {
 		return;
 
 	switch(code) {
+	case KBD_CODE_SPACE:
+		start = true;
+		break;
+
 	case KBD_CODE_UP:
 		dir = NORTH;
 		break;
@@ -142,9 +154,11 @@ static bool point_used(const point_t *p, bool head) {
 	return false;
 }
 
-static void step(void) {
+static bool step(void) {
 	uint8_t d = dir;
 
+	rand_mix(d);
+
 	LedSignSet(tail.x, tail.y, 0);
 
 	int i;
@@ -160,9 +174,8 @@ static void step(void) {
 	go(&pt, d);
 	LedSignSet(pt.x, pt.y, 3);
 
-	if (point_used(&pt, true)) {
-		while(true) {}
-	}
+	if (point_used(&pt, true))
+		return false;
 
 	if (points_equal(&pt, &q)) {
 		rand_q();
@@ -173,26 +186,30 @@ static void step(void) {
 		move(d, false);
 	}
 
-	if (point_used(&pt, false)) {
-		while(true) {}
-	}
+	if (point_used(&pt, false))
+		return false;
 
 	LedSignSet(q.x, q.y, 7);
+
+	return true;
 }
 
 int main() {
 	LedSignInit(GRAYSCALE);
 	kbd_init();
 
-	reset();
-
 	sei();
 
 	kbd_send(KBD_CMD_RESET);
 
 	while(true) {
-		step();
-		_delay_ms(100);
+		while (!start) {}
+		start = false;
+
+		reset();
+
+		while (step())
+			_delay_ms(100);
 	}
 
 	return 0;
-- 
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