time to save again, added a system clock so we can check temperature every 250ms and run a PID loop

mendel/Makefile

@@ -14,7 +14,7 @@
 
 PROGRAM = mendel
 
-SOURCES = $(PROGRAM).c ringbuffer.c serial.c dda.c gcode.c timer.c
+SOURCES = $(PROGRAM).c ringbuffer.c serial.c dda.c gcode.c timer.c clock.c temp.c
 
 ##############################################################################
 #                                                                            #

mendel/clock.c

@@ -0,0 +1,53 @@
+/*
+	clock.c
+
+	a system clock with 1ms ticks
+*/
+
+#include	"clock.h"
+
+#include	<avr/io.h>
+#include	<avr/interrupt.h>
+
+#include	"arduino.h"
+
+// global clock
+volatile uint32_t	clock = 0;
+
+// 1/4 second tick
+uint8_t						clock_counter_250ms = 0;
+volatile uint8_t	clock_flag_250ms = 0;
+
+void clock_setup() {
+	// use system clock
+	ASSR = 0;
+	// no compare match, CTC mode
+	TCCR2A = MASK(WGM21);
+	// 128 prescaler (16MHz / 128 = 125KHz)
+	TCCR2B = MASK(CS22) | MASK(CS20);
+	// 125KHz / 125 = 1KHz for a 1ms tick rate
+	OCR2A = 125;
+	// interrupt on overflow, when counter reaches OCR2A
+	TIMSK2 |= MASK(TOIE2);
+}
+
+ISR(TIMER2_OVF_vect) {
+	// global clock
+	clock++;
+
+	// 1/4 second tick
+	if (++clock_counter_250ms == 250) {
+		clock_flag_250ms = 255;
+		clock_counter_250ms = 0;
+	}
+}
+
+uint32_t clock_read() {
+	uint32_t	c;
+
+	cli();			// set atomic
+	c = clock;	// copy clock value
+	sei();			// release atomic
+
+	return c;
+}

mendel/clock.h

@@ -0,0 +1,13 @@
+#ifndef	_CLOCK_H
+#define	_CLOCK_H
+
+#include	<stdint.h>
+
+void			clock_setup(void);
+uint32_t	clock_read(void);
+
+extern volatile uint8_t	clock_flag_250ms;
+
+#define	CLOCK_FLAG_250MS_TEMPCHECK	1
+
+#endif	/* _CLOCK_H */

mendel/machine.h

@@ -24,13 +24,4 @@
 #define	STEPS_PER_MM_Z				(3200)
 #define	STEPS_PER_MM_E				(EXTRUDER_STEPS_PER_REV * EXTRUDER_SHAFT_RADIUS * PI * EXTRUDER_INLET_DIAMETER / EXTRUDER_NOZZLE_DIAMETER)
 
-/*
-	heater PID variables
-	used as int16_t * FACTOR so don't put brackets around them
-*/
-
-#define	P_FACTOR	133 / 1024
-#define	I_FACTOR	17 / 1024
-#define	D_FACTOR  180 / 1024
-
 #endif	/* _MACHINE_H */

mendel/mendel.c

@@ -5,13 +5,14 @@
 #include	<avr/io.h>
 #include	<avr/interrupt.h>
 
-#include	"serial.h"
+#include	"machine.h"
 
+#include	"serial.h"
 #include	"dda.h"
 #include	"gcode.h"
 #include	"timer.h"
-
-#include	"machine.h"
+#include	"clock.h"
+#include	"temp.h"
 
 uint8_t	option_bitfield;
 
@@ -46,17 +47,30 @@ int main (void)
 
 	WRITE(HEATER_PIN, 0);	SET_OUTPUT(HEATER_PIN);
 
+	WRITE(SCK, 0);	SET_OUTPUT(SCK);
+	WRITE(MISO, 1);	SET_INPUT(MISO);
+	WRITE(SS, 0);		SET_OUTPUT(SS);
+
+
 	// set up timers
 	setupTimerInterrupt();
 
 	// enable interrupts
 	sei();
 
+	serial_writeblock((uint8_t *) "Start\n", 6);
+
+	// main loop
 	for (;;)
 	{
-		for (;serial_rxchars() == 0;);
-		uint8_t c = serial_popchar();
+		if (serial_rxchars()) {
+			uint8_t c = serial_popchar();
+			scan_char(c);
+		}
 
-		scan_char(c);
+		if (clock_flag_250ms & CLOCK_FLAG_250MS_TEMPCHECK) {
+			clock_flag_250ms &= ~CLOCK_FLAG_250MS_TEMPCHECK;
+			temp_tick();
+		}
 	}
 }

mendel/temp.c

@@ -8,22 +8,20 @@
 
 #include	"machine.h"
 #include	"pinout.h"
+#include	"clock.h"
 
-uint16_t	current_temp;
-uint16_t	target_temp;
+uint16_t	current_temp = 0;
+uint16_t	target_temp  = 0;
 
-int16_t		heater_p;
-int16_t		heater_i;
-int16_t		heater_d;
+int16_t		heater_p     = 0;
+int16_t		heater_i     = 0;
+int16_t		heater_d     = 0;
 
-void temp_setup() {
-	SET_OUTPUT(SCK);
-	SET_INPUT(MISO);
-	SET_OUTPUT(SS);
+int16_t		p_factor			= 680;
+int16_t		i_factor			= 18;
+int16_t		d_factor			= 200;
 
-	WRITE(SS, 0);
-	WRITE(SCK, 0);
-}
+#define		PID_SCALE			1024
 
 uint16_t temp_read() {
 	uint16_t temp;
@@ -71,7 +69,7 @@ void temp_tick() {
 	// note: D follows temp rather than error so there's no large derivative when the target temperature changes
 	heater_d = (current_temp - last_temp);
 
-	int16_t pid_output = (heater_p * P_FACTOR) + (heater_i * I_FACTOR) + (heater_d * D_FACTOR);
+	int16_t pid_output = ((heater_p * p_factor) + (heater_i * i_factor) + (heater_d * d_factor)) / PID_SCALE;
 
 #ifdef	HEATER_PIN_PWMABLE
 	HEATER_PIN_PWMABLE = pid_output

mendel/temp.h

@@ -3,7 +3,6 @@
 
 #include	<stdint.h>
 
-void temp_setup(void);
 uint16_t temp_read(void);
 void temp_set(uint16_t t);
 void temp_tick(void);