diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1e03693..c1b29b1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -19,7 +19,7 @@ pico_sdk_init()
 
 # Add executable. Default name is the project name, version 0.1
 
-add_executable(uSDR uSDR.c lcd.c si5351.c dsp.c)
+add_executable(uSDR uSDR.c lcd.c si5351.c dsp.c monitor.c)
 
 pico_set_program_name(uSDR "uSDR")
 pico_set_program_version(uSDR "0.1")
@@ -31,9 +31,12 @@ target_link_libraries(uSDR pico_stdlib)
 pico_enable_stdio_uart(uSDR 0)
 pico_enable_stdio_usb(uSDR 1)
 
+
 # Add any user requested libraries
 target_link_libraries(uSDR
-        hardware_i2c
+        pico_stdlib
+		pico_multicore
+		hardware_i2c
 		hardware_pwm
         hardware_pio
         hardware_timer
diff --git a/dsp.c b/dsp.c
index fc040cd..ac66e1b 100644
--- a/dsp.c
+++ b/dsp.c
@@ -2,11 +2,12 @@
  * dsp.c
  *
  * Created: Mar 2021
- * Author: Arjan
+ * Author: Arjan te Marvelde
  * 
- * Signal processing of RX and TX branch
- * Each branch has a dedicated timer routine that runs on set times.
- * The callback period is set with RX_US and TX_US, e.g. 16 means every 16 usec, or 62.5 kHz.
+ * Signal processing of RX and TX branch, to be run on the second processor core.
+ * Each branch has a dedicated routine that must run on set times.
+ * The period is determined by reads from the inter-core fifo, by the dsp_loop() routine. 
+ * This fifo is written from core0 from a 16us timer callback routine (i.e. 62.5kHz)
  *
  * The RX branch:
  * - Sample I and Q QSD channels intermittently, and shift into I and Q delay line (31.25 kHz per channel)
@@ -19,7 +20,7 @@
  *
  * The TX branch:
  * - Sample the Audio input channel (62.5 kHz)
- * - Low pass filter: Fc=4kHz
+ * - Low pass filter: Fc=3kHz
  * - Eight rate (7.8125 kHz) to improve low F behavior of Hilbert transform
  * - Generate Q samples by doing a Hilbert transform
  * - Push I and Q to QSE output DACs
@@ -27,8 +28,12 @@
  */
 
 #include "pico/stdlib.h"
+#include "pico/multicore.h"
 #include "hardware/pwm.h"
 #include "hardware/adc.h"
+#include "hardware/irq.h"
+#include "hardware/timer.h"
+#include "hardware/clocks.h"
 
 #include "dsp.h"
 
@@ -65,8 +70,10 @@ uint16_t wave4[64] =
  * Exact time is obtained by passing the value negative.
  * Here we use 16us (62.5 kHz == PWM freq/4 [or 8]) 
  */
-#define RX_US		16
-#define TX_US		16
+#define DSP_US		16
+#define DSP_TX		1
+#define DSP_RX		2
+
 
 /* 
  * Low pass filters Fc=3, 7 and 15 kHz (see http://t-filter.engineerjs.com/)
@@ -84,19 +91,16 @@ volatile uint16_t dac_iq, dac_audio;
 volatile bool tx_enabled;
 
 
-/* RX TIMER and callback */
+/* CORE1: RX branch */
 volatile int16_t i_s[15], q_s[15], i_dc, q_dc, i_prev;
-struct repeating_timer rx_timer;
-bool rx_callback(struct repeating_timer *t) 
+bool rx(void) 
 {
 	static bool q_phase;
 	int16_t sample;
 	int32_t accu;
 	int16_t qh;
 	int i;
-	
-	if (tx_enabled) return(true);					// Early bailout when TX-ing
-	
+		
 	if (q_phase)
 	{
 		adc_select_input(1);						// Q channel ADC 
@@ -170,19 +174,16 @@ bool rx_callback(struct repeating_timer *t)
 }
 
 
-/* TX TIMER and callback */
+/* CORE1: TX branch */
 volatile int16_t a_s_pre[15], a_s[15], a_dc;
-struct repeating_timer tx_timer;
-bool tx_callback(struct repeating_timer *t) 
+bool tx(void) 
 {
 	static int tx_phase = 0;
 	int16_t sample;
 	int32_t accu;
 	int16_t qh;
 	int i;
-	
-	if (!tx_enabled) return(true);
-	
+		
 	/*
 	 * Get sample and shift into delay line
 	 */
@@ -233,7 +234,37 @@ bool tx_callback(struct repeating_timer *t)
 }
 
 
-int dsp_init()
+/* CORE1: Timing loop, triggered through inter-core fifo */
+void dsp_loop()
+{
+	uint32_t cmd;
+	
+    while(1) 
+	{
+        cmd = multicore_fifo_pop_blocking();		// Wait for fifo output
+		if (cmd == DSP_TX)
+			tx();
+		else
+			rx();
+    }
+}
+
+
+/* CORE0: Timer callback, triggers core1 through inter-core fifo */
+struct repeating_timer dsp_timer;
+bool dsp_callback(struct repeating_timer *t) 
+{
+	//if (tx_enabled)
+		multicore_fifo_push_blocking(DSP_TX);		// Write TX in fifo to core 1
+	//else
+		multicore_fifo_push_blocking(DSP_RX);		// Write RX in fifo to core 1
+	
+	return true;
+}
+
+
+/* CORE0: Initialize dsp context and spawn core1 process */
+void dsp_init() 
 {
 	uint16_t slice_num;
 	
@@ -259,9 +290,8 @@ int dsp_init()
 	adc_select_input(0);							// Select ADC 0 
 
 	tx_enabled = false;								// RX mode
-		
-	//add_repeating_timer_us(-TX_US, tx_callback, NULL, &tx_timer);
-	add_repeating_timer_us(-RX_US, rx_callback, NULL, &rx_timer);
 
-    return 0;
+    multicore_launch_core1(dsp_loop);				// Start processing on core1
+	add_repeating_timer_us(-DSP_US, dsp_callback, NULL, &dsp_timer);
 }
+
diff --git a/dsp.h b/dsp.h
index 263b5a1..613c7e1 100644
--- a/dsp.h
+++ b/dsp.h
@@ -1,11 +1,19 @@
 #ifndef __DSP_H__
 #define __DSP_H__
+/* 
+ * dsp.h
+ *
+ * Created: Mar 2021
+ * Author: Arjan te Marvelde
+ *
+ * See dsp.c for more information 
+ */
 
 #include "pico/stdlib.h"
 #include "hardware/adc.h"
 #include "hardware/pwm.h"
 
 
-int dsp_init();
+void dsp_init();
 
 #endif
diff --git a/lcd.c b/lcd.c
index 6522686..55c44b0 100644
--- a/lcd.c
+++ b/lcd.c
@@ -1,4 +1,9 @@
 /*
+ * lcd.c
+ *
+ * Created: Mar 2021
+ * Author: Arjan te Marvelde
+ * 
  * Grove 16x2 LCD, HD44780 chip with JHD1804 I2C interface
  * Display RAM addresses 0x00-0x1f for top row and 0x40-0x5f for bottom row
  *
diff --git a/lcd.h b/lcd.h
index 4c834fc..1f7bd01 100644
--- a/lcd.h
+++ b/lcd.h
@@ -1,5 +1,13 @@
 #ifndef __LCD_H__
 #define __LCD_H__
+/* 
+ * lcd.h
+ *
+ * Created: Mar 2021
+ * Author: Arjan te Marvelde
+ *
+ * See lcd.c for more information 
+ */
 
 #include "pico/stdlib.h"
 #include "hardware/i2c.h"
diff --git a/monitor.c b/monitor.c
new file mode 100644
index 0000000..04797df
--- /dev/null
+++ b/monitor.c
@@ -0,0 +1,92 @@
+/*
+ * monitor.c
+ *
+ * Created: Mar 2021
+ * Author: Arjan te Marvelde
+ * 
+ * Command shell on stdin/stdout.
+ * Collects characters and parses commandstring.
+ */ 
+
+#include <stdio.h>
+#include <string.h>
+#include "pico/stdlib.h"
+
+#include "si5351.h"
+#include "monitor.h"
+
+/* Monitor definitions */
+#define ENDSTDIN	255
+#define CR			13
+#define LF			10
+#define CMD_LEN		32
+
+
+char mon_cmd[CMD_LEN+1];
+
+
+uint8_t si5351_reg[200];
+
+/* Commandstring parser */
+char delim[] = " ";
+#define NCMD	3
+char *shell[NCMD] = {"si", "fa", "fb"};
+void mon_parse(char* s)
+{
+	char *p;
+	int base, nreg, i;
+
+	p = strtok(s, delim); 							// Get command part of string
+	for (i=0; i<NCMD; i++)
+		if (strcmp(p, shell[i]) == 0) break;
+	switch(i)
+	{
+	case 0:
+		// Next: p = strtok(NULL, delim); (returns NULL if none left)
+		for (i=0; i<nreg; i++) si5351_reg[i] = 0xaa;
+		si_getreg(si5351_reg, (uint8_t)base, (uint8_t)nreg);
+		for (i=0; i<nreg; i++) printf("%02x ",(int)(si5351_reg[i]));
+		printf("\n");
+		break;
+	case 1:
+		printf("%s\n", p);
+		break;
+	case 2:
+		printf("%s\n", p);
+		break;
+	default:
+		break;
+	}
+}
+
+void mon_init()
+{
+	/* Initialize IOs */
+    stdio_init_all();
+}
+
+void mon_read(uint32_t timeout)
+{
+	int i = 0;
+	int c = getchar_timeout_us(timeout);
+	switch (c)
+	{
+	case PICO_ERROR_TIMEOUT:						// just go-on
+		break;
+	case CR:										// CR or LF:
+	case LF:										// 		need to parse command string
+		putchar((char)c);							// echo character
+		if (i==0) break;							// already did a parse, only do it once
+		mon_cmd[i] = 0;								// terminate command string
+		i=0;										// reset index
+		mon_parse(mon_cmd);							// process command
+		printf("Pico> ");							// prompt
+		break;
+	default:
+		if ((c<32)||(c>=128)) break;				// Alfanumeric?
+		putchar((char)c);							// echo character
+		mon_cmd[i] = (char)c;						// store in command string
+		if (i<CMD_LEN) i++;							// check range and increment
+		break;
+	}
+}
diff --git a/monitor.h b/monitor.h
new file mode 100644
index 0000000..96bbd7d
--- /dev/null
+++ b/monitor.h
@@ -0,0 +1,15 @@
+#ifndef __MONITOR_H__
+#define __MONITOR_H__
+/* 
+ * monitor.h
+ *
+ * Created: Mar 2021
+ * Author: Arjan te Marvelde
+ *
+ * See monitor.c for more information 
+ */
+
+void mon_init();
+void mon_read(uint32_t timeout);
+
+#endif
\ No newline at end of file
diff --git a/si5351.c b/si5351.c
index 6c0961b..6d3c604 100644
--- a/si5351.c
+++ b/si5351.c
@@ -1,8 +1,8 @@
 /*
  * si5351.c
  *
- * Created: 12 Jan 2020 21:45:00
- *  Author: Arjan
+ * Created: Jan 2020
+ * Author: Arjan
  
 Si5351 principle:
 =================
@@ -117,21 +117,6 @@ Control Si5351:
 
  */ 
 
-/*
-  Implicit type conversion precedence:
-  - long double
-  - double
-  - float
-  - unsigned long int
-  - long int
-  - unsigned int
-  - int
-  - other
-  conversion is always to highest type, this is also the result of an operation.
-  
-  Maximum UL = 4,294,967,295 (0xffffffff)
- */
-
 #include <stdio.h>
 #include <math.h>
 #include "pico/stdlib.h"
@@ -190,6 +175,7 @@ Control Si5351:
 
 vfo_t vfo[2];				// 0: clk0 and clk1     1: clk2
 
+/* read contents of SI5351 registers, from reg to reg+len-1, output in data array */
 int si_getreg(uint8_t *data, uint8_t reg, uint8_t len)
 {
 	int ret;
@@ -304,7 +290,7 @@ void si_setmsi(uint8_t i)
 // If in range, just set MSN registers
 // If not in range, recalculate MSi and Ri and also MSN
 // Set MSN, MSi and Ri registers (implicitly resets PLL)
-void vfo_evaluate(void)
+void si_evaluate(void)
 {
 	float msn;
 
@@ -342,7 +328,7 @@ void vfo_evaluate(void)
 
 
 // Initialize the Si5351 VFO registers
-void vfo_init(void)
+void si_init(void)
 {
 	uint8_t data[16];		// I2C trx buffer
 
@@ -358,7 +344,7 @@ void vfo_init(void)
 	// MSN=27.2   P1=2969, P2=600000, P3=1000000
 	vfo[0].freq  = 10000000;
 	vfo[0].flag  = 0;
-	vfo[0].phase = 2;
+	vfo[0].phase = 1;
 	vfo[0].ri    = 1;
 	vfo[0].msi   = 68;
 	vfo[0].msn   = 27.2;
@@ -434,6 +420,5 @@ void vfo_init(void)
 	data[0] = SI_CLK_OE;
 	data[1] = 0x00;
 	i2c_write_blocking(i2c1, I2C_VFO, data, 2, false);
-
 }
 
diff --git a/si5351.h b/si5351.h
index f83679f..2778418 100644
--- a/si5351.h
+++ b/si5351.h
@@ -3,8 +3,11 @@
 /*
  * si5351.h
  *
- * Created: 13 March 2021
+ * Created: March 2021
  * Author: Arjan
+ *
+ * See si5351.c for more information 
+ *
  */ 
 
 
@@ -21,13 +24,13 @@ typedef struct
 extern vfo_t vfo[2];	// Table contains all control data for three clk outputs, but 0 and 1 are coupled in vfo[0]
 
 int  si_getreg(uint8_t *data, uint8_t reg, uint8_t len);
-void vfo_init(void);
-void vfo_evaluate(void);
-
+void si_init(void);
+void si_evaluate(void);
 
 #define SI_GETFREQ(i)		((((i)>=0)&&((i)<2))?vfo[(i)].freq:0)
 #define SI_INCFREQ(i, d)	if ((((i)>=0)&&((i)<2))&&((vfo[(i)].freq)<(150000000-(d)))) { vfo[(i)].freq += (d); vfo[(i)].flag = 1;}
 #define SI_DECFREQ(i, d)	if ((((i)>=0)&&((i)<2))&&((vfo[(i)].freq)>(d))) { (vfo[(i)].freq) -= (d); vfo[(i)].flag = 1;}
 #define SI_SETFREQ(i, f)	if ((((i)>=0)&&((i)<2))&&((f)<150000000)) { vfo[(i)].freq = (f); vfo[(i)].flag = 1;}
+#define SI_SETPHASE(i, p)	if (((i)>=0)&&((i)<2)) {vfo[(i)].phase = ((uint8_t)p)&3; vfo[(i)].flag = 1;}
 
 #endif /* _SI5351_H */
\ No newline at end of file
diff --git a/uSDR.c b/uSDR.c
index f7b2dd2..32944c0 100644
--- a/uSDR.c
+++ b/uSDR.c
@@ -1,7 +1,21 @@
+/*
+ * uSDR.c
+ *
+ * Created: Mar 2021
+ * Author: Arjan te Marvelde
+ * 
+ * The main loop of the application.
+ * This initializes the units that do the actual work, and then loops in the background. 
+ * Other units are:
+ * - dsp.c, containing all signal processing in RX and TX branches. This part runs on the second processor core.
+ * - si5351.c, containing all controls for setting up the si5351 clock generator.
+ * - lcd.c, contains all functions to put something on the LCD
+ * - hmi.c, contains all functions that handle user inputs
+ */
+
 #include <stdio.h>
 #include <string.h>
 #include "pico/stdlib.h"
-#include "hardware/pwm.h"
 #include "hardware/pio.h"
 #include "hardware/timer.h"
 #include "hardware/clocks.h"
@@ -9,20 +23,13 @@
 #include "lcd.h"
 #include "dsp.h"
 #include "si5351.h"
+#include "monitor.h"
 
 
-
-/* Monitor definitions */
-#define ENDSTDIN	255
-#define CR			13
-#define LF			10
-#define CMD_LEN		32
-
 uint8_t display1[16];
 uint8_t display2[16];
 
 
-
 /* LED TIMER definition and callback */
 struct repeating_timer led_timer;
 bool led_callback(struct repeating_timer *t) 
@@ -35,44 +42,8 @@ bool led_callback(struct repeating_timer *t)
 }
 
 
-uint8_t si5351_reg[200];
-char delim[] = " ";
-#define NCMD	3
-char *shell[NCMD] = {"si", "fa", "fb"};
-void mon_parse(char* s)
-{
-	char *p;
-	int base, nreg, i;
-
-	p = strtok(s, delim); 							// Get command part of string
-	for (i=0; i<NCMD; i++)
-		if (strcmp(p, shell[i]) == 0) break;
-	switch(i)
-	{
-	case 0:
-		// Next: p = strtok(NULL, delim); (returns NULL if none left)
-		for (i=0; i<nreg; i++) si5351_reg[i] = 0xaa;
-		si_getreg(si5351_reg, (uint8_t)base, (uint8_t)nreg);
-		for (i=0; i<nreg; i++) printf("%02x ",(int)(si5351_reg[i]));
-		printf("\n");
-		break;
-	case 1:
-		printf("%s\n", p);
-		break;
-	case 2:
-		printf("%s\n", p);
-		break;
-	default:
-		break;
-	}
-}
-
-
-
 int main()
 {
-	/* Initialize IOs */
-    stdio_init_all();
 
 	/* Initialize LED pin output */
 	gpio_init(PICO_DEFAULT_LED_PIN);
@@ -80,51 +51,24 @@ int main()
 	gpio_put(PICO_DEFAULT_LED_PIN, true);			// Set LED on
 	add_repeating_timer_ms(-1000, led_callback, NULL, &led_timer);
 
-	/* Initialize PWM */
-	dsp_init();
+	/* Initialize units */
+	si_init();										// VFO control unit
+	lcd_init();										// LCD output unit
+	dsp_init();										// Signal processing unit
 	
-	/* Initialize Si5351 vfo */
-	vfo_init();
-
-	/* Initialize LCD */
-	lcd_init();
 	lcd_ctrl(LCD_GOTO, 0, 0);
 	sprintf(display1, "A: 7074.0 kHz");
 	lcd_write(display1,13);
-	
 	SI_SETFREQ(0, 2*7074000UL);						// Set freq to 2*7074 kHz
+	SI_SETPHASE(0,2);								// Set phase to 180deg
 	
-	/* Initialize monitor terminal */
-	printf("Pico> ");
-	int c, i=0;
-	char mon_cmd[CMD_LEN+1];
 	while (1) 
 	{
 		/* Check for monitor input */
-		c = getchar_timeout_us(100000);				// 1 try per 100 msec
-		switch (c)
-		{
-		case PICO_ERROR_TIMEOUT:					// just go-on
-			break;
-		case CR:									// CR or LF:
-		case LF:									// 		need to parse command string
-			putchar((char)c);						// echo character
-			if (i==0) break;						// already did a parse, only do it once
-			mon_cmd[i] = 0;							// terminate command string
-			i=0;									// reset index
-			mon_parse(mon_cmd);						// process command
-			printf("Pico> ");						// prompt
-			break;
-		default:
-			if ((c<32)||(c>=128)) break;			// Alfanumeric?
-			putchar((char)c);						// echo character
-			mon_cmd[i] = (char)c;					// store in command string
-			if (i<CMD_LEN) i++;						// check range and increment
-			break;
-		}
+		mon_read(100000L);							// Wait max 100msec
 		
 		/* Check whether VFO settings have changed */
-		vfo_evaluate();		
+		si_evaluate();		
 	}
 
     return 0;