diff --git a/src/matrix/matrix.c b/src/matrix/matrix.c
index 947c915..d0b3720 100644
--- a/src/matrix/matrix.c
+++ b/src/matrix/matrix.c
@@ -1,3 +1,4 @@
+#include <libopencm3/cm3/systick.h>
 #include <libopencm3/stm32/rcc.h>
 #include <libopencm3/stm32/gpio.h>
 
@@ -5,6 +6,14 @@
 
 typedef unsigned char byte;
 
+static void delay_ms(unsigned int ms)
+{
+	systick_clear();
+	for (unsigned int i=0; i<ms; i++)
+		while (!systick_get_countflag())
+			;
+}
+
 static void wait(void)
 {
 	for (int i=0; i<7200; i++)
@@ -34,10 +43,7 @@ static void set_reg(int reg, int data)
 	wait();
 }
 
-byte display[8];
-
-#if 0
-static unsigned char smile[8] = {
+static byte display[8] = {
 	0x66,	/* .##..##. */
 	0x66,	/* .##..##. */
 	0x00,	/* ........ */
@@ -47,7 +53,6 @@ static unsigned char smile[8] = {
 	0x66,	/* .##..##. */
 	0x3c,	/* ..####.. */
 };
-#endif
 
 static void refresh_display(void)
 {
@@ -55,69 +60,6 @@ static void refresh_display(void)
 		set_reg(i, display[8-i]);
 }
 
-static signed char dirs[4][2] = {{1,0}, {0,-1}, {-1,0}, {0,1}};
-
-static byte snake_dir;
-#define SNAKE_MAX 65
-static byte snake[SNAKE_MAX][2];
-static byte snake_tail, snake_head;
-static byte food[2];
-static unsigned int rng_state = 0xdeadbeef;
-
-static byte buttons[2];
-
-static void gen_food(void)
-{
-	food[0] = (rng_state >> 28) & 7;
-	food[1] = (rng_state >> 20) & 7;
-	rng_state *= 0x3771cadb;
-}
-
-static void snake_init(void)
-{
-	snake[0][0] = 0;
-	snake[0][1] = 0;
-	snake_dir = 3;
-	snake_tail = 0;
-	snake_head = 1;
-	gen_food();
-}
-
-static void snake_show(void)
-{
-	memset(display, 0, 8);
-	for (int i=snake_tail; i != snake_head; i = (i+1) % SNAKE_MAX)
-		display[snake[i][0]] |= 1 << snake[i][1];
-	display[food[0]] |= 1 << food[1];
-	refresh_display();
-}
-
-static void snake_step(void)
-{
-	if (buttons[0])
-		snake_dir = (snake_dir+3) % 4;
-	else if (buttons[1])
-		snake_dir = (snake_dir+1) % 4;
-
-	int hi = (snake_head + SNAKE_MAX - 1) % SNAKE_MAX;
-	int x = snake[hi][0] + dirs[snake_dir][0];
-	int y = snake[hi][1] + dirs[snake_dir][1];
-
-	if (x < 0 || x > 7 || y < 0 || y > 7)
-		return;
-
-	snake[snake_head][0] = x;
-	snake[snake_head][1] = y;
-	snake_head = (snake_head + 1) % SNAKE_MAX;
-
-	if (x == food[0] && y == food[1])
-		gen_food();
-	else
-		snake_tail = (snake_tail + 1) % SNAKE_MAX;
-
-	snake_show();
-}
-
 int main(void)
 {
 	rcc_clock_setup_pll(&rcc_hse_configs[RCC_CLOCK_HSE8_72MHZ]);
@@ -136,10 +78,12 @@ int main(void)
 	gpio_set(GPIOB, GPIO13);
 	gpio_clear(GPIOB, GPIO14);
 
+#if 0
 	// PA0 = left button
 	// PA1 = right button
 	gpio_set_mode(GPIOA, GPIO_MODE_INPUT, GPIO_CNF_INPUT_PULL_UPDOWN, GPIO0 | GPIO1);
 	gpio_set(GPIOA, GPIO0 | GPIO1);
+#endif
 
 	refresh_display();
 	set_reg(9, 0);
@@ -148,20 +92,10 @@ int main(void)
 	set_reg(13, 0);	// test
 	set_reg(12, 1);	// shutdown
 
-	snake_init();
-	snake_show();
-
 	for (;;) {
-		buttons[0] = buttons[1] = 0;
-		for (int i=0; i<1000000; i++) {
-			if (!gpio_get(GPIOA, GPIO0))
-				buttons[0] = 1;
-			if (!gpio_get(GPIOA, GPIO1))
-				buttons[1] = 1;
-			asm volatile ("");
-		}
-
-		gpio_toggle(GPIOC, GPIO13);
-		snake_step();
+		gpio_clear(GPIOC, GPIO13);
+		delay_ms(100);
+		gpio_set(GPIOC, GPIO13);
+		delay_ms(500);
 	}
 }