diff --git a/mendel/Makefile b/mendel/Makefile
index 3f035fe..807a84b 100644
--- a/mendel/Makefile
+++ b/mendel/Makefile
@@ -36,7 +36,7 @@ CC = $(ARCH)gcc
 OBJDUMP = $(ARCH)objdump
 OBJCOPY = $(ARCH)objcopy
 
-OPTIMIZE = -Os -ffunction-sections  -finline-functions-called-once -DDEBUG=1
+OPTIMIZE = -Os -ffunction-sections  -finline-functions-called-once -DDEBUG=0
 # OPTIMIZE = -O0
 CFLAGS = -g -Wall -Wstrict-prototypes $(OPTIMIZE) -mmcu=$(MCU_TARGET) -DF_CPU=$(F_CPU) $(DEFS) -std=gnu99 -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -save-temps
 LDFLAGS = -Wl,--as-needed -Wl,--gc-sections
@@ -66,7 +66,7 @@ program: $(PROGRAM).hex
 	@sleep 0.1
 	@stty $(PROGBAUD) raw ignbrk hup < $(PROGPORT)
 	$(AVRDUDE) -cstk500v1 -b$(PROGBAUD) -p$(MCU_TARGET) -P$(PROGPORT) -C/etc/avrdude.conf -U flash:w:$^
-	stty 115200 raw ignbrk -hup -echo ixon < $(PROGPORT)
+	stty 38400 raw ignbrk -hup -echo ixon < $(PROGPORT)
 
 clean:
 	rm -rf *.o *.elf *.lst *.map *.sym *.lss *.eep *.srec *.bin *.hex *.al *.i *.s *~
diff --git a/mendel/dda.c b/mendel/dda.c
index 044fd00..9cea14b 100644
--- a/mendel/dda.c
+++ b/mendel/dda.c
@@ -1,6 +1,7 @@
 #include	"dda.h"
 
 #include	<string.h>
+#include	<avr/interrupt.h>
 
 #include	"timer.h"
 #include	"serial.h"
@@ -375,6 +376,10 @@ void dda_step(DDA *dda) {
 		}
 	}
 
+	// this interrupt can now be interruptible
+	disableTimerInterrupt();
+	sei();
+
 	// this generates too much debug output for all but the slowest step rates
 	if (0 && DEBUG) {
 		serial_writechar('[');
@@ -413,4 +418,8 @@ void dda_step(DDA *dda) {
 	// turn off step outputs, hopefully they've been on long enough by now to register with the drivers
 	// if not, too bad. or insert a (very!) small delay here, or fire up a spare timer or something
 	unstep();
+
+	// reset interruptible so we can return in the same state we started
+	cli();
+	enableTimerInterrupt();
 }
diff --git a/mendel/gcode.c b/mendel/gcode.c
index 48d4da1..48e0a32 100644
--- a/mendel/gcode.c
+++ b/mendel/gcode.c
@@ -109,12 +109,12 @@ void scan_char(uint8_t c) {
 			switch (last_field) {
 				case 'G':
 					next_target.G = read_digit.mantissa;
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_uint8(next_target.G);
 					break;
 				case 'M':
 					next_target.M = read_digit.mantissa;
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_uint8(next_target.M);
 					break;
 				case 'X':
@@ -122,7 +122,7 @@ void scan_char(uint8_t c) {
 						next_target.target.X = decfloat_to_int(&read_digit, STEPS_PER_IN_X, 1);
 					else
 						next_target.target.X = decfloat_to_int(&read_digit, STEPS_PER_MM_X, 1);
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_int32(next_target.target.X);
 					break;
 				case 'Y':
@@ -130,7 +130,7 @@ void scan_char(uint8_t c) {
 						next_target.target.Y = decfloat_to_int(&read_digit, STEPS_PER_IN_Y, 1);
 					else
 						next_target.target.Y = decfloat_to_int(&read_digit, STEPS_PER_MM_Y, 1);
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_int32(next_target.target.Y);
 					break;
 				case 'Z':
@@ -138,7 +138,7 @@ void scan_char(uint8_t c) {
 						next_target.target.Z = decfloat_to_int(&read_digit, STEPS_PER_IN_Z, 1);
 					else
 						next_target.target.Z = decfloat_to_int(&read_digit, STEPS_PER_MM_Z, 1);
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_int32(next_target.target.Z);
 					break;
 				case 'E':
@@ -146,7 +146,7 @@ void scan_char(uint8_t c) {
 						next_target.target.E = decfloat_to_int(&read_digit, STEPS_PER_IN_E, 1);
 					else
 						next_target.target.E = decfloat_to_int(&read_digit, STEPS_PER_MM_E, 1);
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_uint32(next_target.target.E);
 					break;
 				case 'F':
@@ -155,7 +155,7 @@ void scan_char(uint8_t c) {
 						next_target.target.F = decfloat_to_int(&read_digit, 254, 10);
 					else
 						next_target.target.F = decfloat_to_int(&read_digit, 1, 1);
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_uint32(next_target.target.F);
 					break;
 				case 'S':
@@ -169,7 +169,7 @@ void scan_char(uint8_t c) {
 						next_target.S = decfloat_to_int(&read_digit, PID_SCALE, 1);
 					else
 						next_target.S = decfloat_to_int(&read_digit, 1, 1);
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_uint16(next_target.S);
 					break;
 				case 'P':
@@ -178,7 +178,7 @@ void scan_char(uint8_t c) {
 						next_target.P = decfloat_to_int(&read_digit, 1000, 1);
 					else
 						next_target.P = decfloat_to_int(&read_digit, 1, 1);
-					if (DEBUG)
+// 					if (DEBUG)
 						serwrite_uint16(next_target.P);
 					break;
 			}
@@ -195,7 +195,7 @@ void scan_char(uint8_t c) {
 		// new field?
 		if (indexof(c, alphabet) >= 0) {
 			last_field = c;
-			if (DEBUG)
+// 			if (DEBUG)
 				serial_writechar(c);
 		}
 
@@ -264,21 +264,24 @@ void scan_char(uint8_t c) {
 
 	// end of line
 	if ((c == 10) || (c == 13)) {
-		serial_writechar(c);
+// 		if (DEBUG)
+			serial_writechar(c);
 		// process
-		process_gcode_command(&next_target);
+// 		if (next_target.seen_G || next_target.seen_M) {
+			process_gcode_command(&next_target);
 
-		// reset 'seen comment'
-		option_bitfield &= ~OPTION_COMMENT;
+			// reset 'seen comment'
+			option_bitfield &= ~OPTION_COMMENT;
 
-		// reset variables
-		next_target.seen_X = next_target.seen_Y = next_target.seen_Z = next_target.seen_E = next_target.seen_F = next_target.seen_S = next_target.seen_P = 0;
-		last_field = 0;
-		read_digit.sign = 0;
-		read_digit.mantissa = 0;
-		read_digit.exponent = 0;
+			// reset variables
+			next_target.seen_X = next_target.seen_Y = next_target.seen_Z = next_target.seen_E = next_target.seen_F = next_target.seen_S = next_target.seen_P = 0;
+			last_field = 0;
+			read_digit.sign = 0;
+			read_digit.mantissa = 0;
+			read_digit.exponent = 0;
 
-		serial_writestr_P(PSTR("OK\n"));
+			serial_writestr_P(PSTR("OK\n"));
+// 		}
 	}
 }
 
@@ -423,6 +426,7 @@ void process_gcode_command(GCODE_COMMAND *gcmd) {
 		switch (gcmd->M) {
 			// M101- extruder on
 			case 101:
+				serial_writestr_P(PSTR("Waiting for extruder to reach target temperature\n"));
 				// here we wait until target temperature is reached, and emulate main loop so the temperature can actually be updated
 				while (!temp_achieved()) {
 					ifclock(CLOCK_FLAG_250MS) {
diff --git a/mendel/machine.h b/mendel/machine.h
index f3225f5..1155160 100644
--- a/mendel/machine.h
+++ b/mendel/machine.h
@@ -47,7 +47,7 @@
 #define	E_STARTSTOP_STEPS					20
 
 // extruder settings
-#define	TEMP_HYSTERESIS						2
+#define	TEMP_HYSTERESIS						20
 
 /*
 	calculated values - you shouldn't need to touch these
diff --git a/mendel/mendel.c b/mendel/mendel.c
index 3de2207..ebf383f 100644
--- a/mendel/mendel.c
+++ b/mendel/mendel.c
@@ -40,10 +40,10 @@ inline void io_init(void) {
 		WRITE(HEATER_PIN, 0); SET_OUTPUT(HEATER_PIN);
 		#ifdef	HEATER_PWM
 			// setup PWM timer: fast PWM, no prescaler
-			OCR0A = 0;
-			TCCR0A = MASK(COM0A1) | MASK(WGM01) | MASK(WGM00);
+			TCCR0A = MASK(WGM01) | MASK(WGM00);
 			TCCR0B = MASK(CS00);
 			TIMSK0 = 0;
+			OCR0A = 0;
 		#endif
 	#endif
 
@@ -55,7 +55,9 @@ inline void io_init(void) {
 		disable_steppers();
 	#endif
 
+	// setup SPI
 	WRITE(SCK, 0);				SET_OUTPUT(SCK);
+	WRITE(MOSI, 1);				SET_OUTPUT(MOSI);
 	WRITE(MISO, 1);				SET_INPUT(MISO);
 	WRITE(SS, 1);					SET_OUTPUT(SS);
 }
@@ -135,9 +137,9 @@ void clock_250ms() {
 			// Queue
 			print_queue();
 		}
-
 		// temperature
-		temp_print();
+		if (temp_get_target())
+			temp_print();
 	}
 }
 
diff --git a/mendel/pinout.h b/mendel/pinout.h
index 8572058..5b20f43 100644
--- a/mendel/pinout.h
+++ b/mendel/pinout.h
@@ -14,6 +14,10 @@
 
 #define	RESERVED_RXD				DIO0
 #define	RESERVED_TXD				DIO1
+#define	RESERVED_SCK				DIO13
+#define	RESERVED_MISO				DIO12
+#define	RESERVED_MOSI				DIO11
+#define	RESERVED_SS					DIO10
 
 /*
 	user defined pins
@@ -108,8 +112,8 @@
 */
 
 #ifdef	HEATER_PWM
-	#define	enable_heater()			do { OCR0A = 255; } while (0)
-	#define	disable_heater()		do { OCR0A = 0; } while (0)
+	#define	enable_heater()			do { TCCR0A |=  MASK(COM0A1); } while (0)
+	#define	disable_heater()		do { TCCR0A &= ~MASK(COM0A1); } while (0)
 #else
 	#define	enable_heater()			WRITE(HEATER_PIN, 1)
 	#define	disable_heater()		WRITE(HEATER_PIN, 0)
diff --git a/mendel/serial.c b/mendel/serial.c
index 366e96e..6432b5c 100644
--- a/mendel/serial.c
+++ b/mendel/serial.c
@@ -4,7 +4,7 @@
 #include	"arduino.h"
 
 #define		BUFSIZE		64 + sizeof(ringbuffer)
-#define		BAUD		115200
+#define		BAUD		38400
 
 #define		ASCII_XOFF	19
 #define		ASCII_XON		17
diff --git a/mendel/temp.c b/mendel/temp.c
index 7e02164..9fe3e1a 100644
--- a/mendel/temp.c
+++ b/mendel/temp.c
@@ -43,37 +43,28 @@ uint8_t		temp_flags		= 0;
 uint16_t temp_read() {
 	uint16_t temp;
 
-/*	if (DEBUG)
-		serial_writestr_P(PSTR("T["));*/
-
-	// very slow for debugging
-	SPCR = MASK(MSTR) | MASK(SPE) | MASK(SPR1) | MASK(SPR0);
+	SPCR = MASK(MSTR) | MASK(SPE) | MASK(SPR0);
 
+	// enable MAX6675
 	WRITE(SS, 0);
 
+	// ensure 100ns delay - a bit extra is fine
 	delay(1);
 
+	// read MSB
 	SPDR = 0;
 	for (;(SPSR & MASK(SPIF)) == 0;);
 	temp = SPDR;
-
-// 	if (DEBUG)
-// 		serwrite_hex8(temp & 0xFF);
-
 	temp <<= 8;
 
+	// read LSB
 	SPDR = 0;
 	for (;(SPSR & MASK(SPIF)) == 0;);
 	temp |= SPDR;
 
-// 	if (DEBUG)
-// 		serwrite_hex8(temp & 0xFF);
-
+	// disable MAX6675
 	WRITE(SS, 1);
 
-	// turn off SPI system
-// 	SPCR = 0;
-
 	temp_flags = 0;
 	if ((temp & 0x8002) == 0) {
 		// got "device id"
@@ -134,7 +125,7 @@ void temp_print() {
 		else {
 			serial_writechar('0');
 		}
-		serial_writestr_P(PSTR("°C"));
+// 		serial_writestr_P(PSTR("°C"));
 	}
 	serial_writechar('\n');
 }
@@ -143,15 +134,15 @@ void temp_tick() {
 	uint16_t last_temp = current_temp;
 	temp_read();
 
-	if (DEBUG)
-		serial_writestr_P(PSTR("T{"));
+// 	if (DEBUG)
+// 		serial_writestr_P(PSTR("T{"));
 
 	int16_t	t_error = target_temp - current_temp;
 
-	if (DEBUG) {
-		serial_writestr_P(PSTR("E:"));
-		serwrite_int16(t_error);
-	}
+// 	if (DEBUG) {
+// 		serial_writestr_P(PSTR("E:"));
+// 		serwrite_int16(t_error);
+// 	}
 
 	// PID stuff
 	// proportional
@@ -187,10 +178,10 @@ void temp_tick() {
 	else
 		pid_output = (pid_output_intermed + 128);
 
-	if (DEBUG) {
-		serial_writestr_P(PSTR("O:"));
-		serwrite_uint8(pid_output);
-	}
+// 	if (DEBUG) {
+// 		serial_writestr_P(PSTR(",O:"));
+// 		serwrite_uint8(pid_output);
+// 	}
 
 #ifdef	HEATER_PWM
 	HEATER_PWM = pid_output;
@@ -203,6 +194,6 @@ void temp_tick() {
 	}
 #endif
 
-	if (DEBUG)
-		serial_writechar('}');
+// 	if (DEBUG)
+// 		serial_writechar('}');
 }