# HG changeset patch
# User John Tsiombikas <nuclear@member.fsf.org>
# Date 1314328560 -10800
# Node ID f883847a059114ecdd658d8fcb7dfbfe5208df1b
# Parent  c0c68988bcdffa9d39178599b88b0e48ee2b7479
foo

diff -r c0c68988bcdf -r f883847a0591 odometer.c
--- a/odometer.c	Thu Aug 25 08:22:19 2011 +0300
+++ b/odometer.c	Fri Aug 26 06:16:00 2011 +0300
@@ -36,7 +36,8 @@
 #define PD_DATA_MASK	0xf
 #define PD_LEDS_MASK	0xc0
 
-#define RPS_TO_KMH(x)	((36 * WHEEL_PERIMETER * (x)) / 1000)
+/* 1800 2sec intervals per hour, \times perimeter, \times x, \over 100000 cm in a kilometer */
+#define RP2S_TO_KMH(x)	((18 * WHEEL_PERIMETER * (x)) / 1000)
 
 #define DEBOUNCE_TICKS	1
 
@@ -49,7 +50,7 @@
 
 void init_timer(void);
 void latch(int n);
-void update_display(void);
+void update_display(int idx);
 void disp_speed(int n);
 void disp_dist(int n);
 void disp_leds(int n);
@@ -60,7 +61,7 @@
 volatile long ticks;
 
 unsigned long nrot;
-unsigned long speed_rps;
+unsigned long speed_rp2s;
 
 int main(void)
 {
@@ -148,28 +149,29 @@
 		if(state) {
 			nrot++;
 
-			update_display();
+			/*update_display();*/
 		}
+		prev_time = ticks;
 	}
-
-	prev_time = ticks;
 }
 
 ISR(TIMER0_OVF_vect)
 {
-	volatile static int sec_ticks;
-	volatile static unsigned long last_rot;
+	volatile static int sec_ticks, sec;
+	volatile static unsigned long last_rot[4];
 
 	ticks++;
 	sec_ticks++;
 
-	if(sec_ticks >= SEC_TICKS) {
-		speed_rps = nrot - last_rot;
+	if(sec_ticks >= SEC_TICKS / 2) {
+		int idx = ++sec & 3;
 
-		update_display();
+		speed_rp2s = nrot - last_rot[idx];
+
+		update_display(idx);
 
 		sec_ticks = 0;
-		last_rot = nrot;
+		last_rot[idx] = nrot;
 	}
 
 
@@ -183,11 +185,11 @@
 	}
 }
 
-void update_display(void)
+void update_display(int idx)
 {
 	if(debug_mode) {
 		disp_dist(nrot);
-		disp_speed(speed_rps);
+		disp_speed(speed_rp2s);
 
 		if(state) {
 			PORTD |= (1 << 5);
@@ -196,7 +198,7 @@
 		}
 	} else {
 		unsigned long dist_cm = (nrot * WHEEL_PERIMETER);
-		int speed_kmh = RPS_TO_KMH(speed_rps);
+		int speed_kmh = RP2S_TO_KMH(speed_rp2s);
 
 		disp_dist(dist_cm / 10000);
 		disp_speed(speed_kmh);