Differences

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--- code:ground_control [2008/11/13 00:39] – laurenceb
+++ code:ground_control [2008/11/13 09:50] (current) – laurenceb
@@ Line 1: / Line 1: @@
 ===== Input capture based version =====
 This uses the input capture function on timer1 (atmega168). The ICNC1 bit in the TCCR1B register need to be set to enable oversampling to give more noise tolerance. A second function running approx every 20ms is needed to decrement counter by two and check if counter>=30. If this is the case there is a valid pwm stream and the diff variable can be used to set the pwm output.
 ==== Header ====
 <code c>
-#define enable_ground_control	TIMSK1|=(1<<ICIE1)			//enables the input capture interrupt
+void enable_ground_control();						//enables the input capture interrupt
-#define disable_ground_control	TIMSK1&=~(1<<ICIE1)			//disables input capture interrupt
+void disable_ground_control();						//disables input capture interrupt
+#define PULSE_MIN (s16)(0.001*(float)F_CPU/16.0)			//pwm must be in the range 1 to 2 ms
+#define PULSE_MAX (s16)(0.002*(float)F_CPU/16.0)			//due to the bit shift we divide by 16
+#define GROUND_LED_ON PORTD|=(1<<3)
+#define GROUND_LED_OFF PORTD&=~(1<<3)
+#define GROUND_LED_SET PORTD&(1<<3)
+void run_ground_control();
+</code>
-#define PULSE_MIN 0.001*F_CPU/8;					//pwm must be in the range 1 to 2 ms
-#define PULSE_MAX 0.002*F_CPU/8;
-</code>
 ====Main code===
@@ Line 19: / Line 21: @@
 #include "main.h"
 extern volatile u08 counter;					//globals
-extern volatile s16 diff;
+extern volatile u16 diff;
@@ Line 35: / Line 37: @@
 		if(!(counter&0x80))				//the lock bit isn't set, so we are free to run
 		{
-			diff=(s16)(ICR1>>1)-(s16)(start>>1);	//set the global volatile s16 diff
+			diff=ICR1;					//set the global volatile s16 diff
-			if(start>ICR1)				//our pwm pulse spans a timer overflow
+			if(start>diff)				//our pwm pulse spans a timer overflow
 			{
-				diff+=(s16)(TOP_COUNT>>1);
+				diff+=TOP_COUNT;
 			}
+			diff-=start;
 			if(diff>PULSE_MIN && diff<PULSE_MAX)	//test against criterion
 			{
@@ Line 60: / Line 63: @@
 	{
 		counter|=0x80;								//lock the diff variable using the counter flag bit
-		OCR1B=((u16)diff)<<1;
+		OCR1B=diff;
 		counter&=~0x80;
 		GROUND_LED_ON;