diff --git a/soc/runtime/Makefile b/soc/runtime/Makefile
index 43238912f..e8b1bb820 100644
--- a/soc/runtime/Makefile
+++ b/soc/runtime/Makefile
@@ -3,7 +3,7 @@ include $(MSCDIR)/software/common.mak
 BOARD=papilio_pro
 SERIAL=/dev/ttyUSB1
 
-OBJECTS=isr.o elf_loader.o main.o
+OBJECTS=isr.o elf_loader.o symbols.o corecom_serial.o gpio.o rtio.o dds.o main.o
 
 all: runtime.bin
 
diff --git a/soc/runtime/corecom.h b/soc/runtime/corecom.h
new file mode 100644
index 000000000..c0ac37e9b
--- /dev/null
+++ b/soc/runtime/corecom.h
@@ -0,0 +1,8 @@
+#ifndef __CORECOM_H
+#define __CORECOM_H
+
+int ident_and_download_kernel(void *buffer, int maxlength);
+int rpc(int rpc_num, int n_args, ...);
+void kernel_finished(void);
+
+#endif /* __CORECOM_H */
diff --git a/soc/runtime/corecom_serial.c b/soc/runtime/corecom_serial.c
new file mode 100644
index 000000000..bb39b0ba9
--- /dev/null
+++ b/soc/runtime/corecom_serial.c
@@ -0,0 +1,128 @@
+#include <stdarg.h>
+#include <crc.h>
+#include <uart.h>
+#include <generated/csr.h>
+
+#include "corecom.h"
+
+enum {
+	MSGTYPE_REQUEST_IDENT		= 0x01,
+	MSGTYPE_LOAD_KERNEL			= 0x02,
+	MSGTYPE_KERNEL_FINISHED		= 0x03,
+	MSGTYPE_RPC_REQUEST			= 0x04,
+};
+
+static int receive_int(void)
+{
+	unsigned int r;
+	int i;
+
+	r = 0;
+	for(i=0;i<4;i++) {
+		r <<= 8;
+		r |= (unsigned char)uart_read();
+	}
+	return r;
+}
+
+static char receive_char(void)
+{
+	return uart_read();
+}
+
+static void send_int(int x)
+{
+	int i;
+
+	for(i=0;i<4;i++) {
+		uart_write((x & 0xff000000) >> 24);
+		x <<= 8;
+	}
+}
+
+static void send_sint(short int i)
+{
+	uart_write((i >> 8) & 0xff);
+	uart_write(i & 0xff);
+}
+
+static void send_char(char c)
+{
+	uart_write(c);
+}
+
+static void receive_sync(void)
+{
+	char c;
+	int recognized;
+
+	recognized = 0;
+	while(recognized < 4) {
+		c = uart_read();
+		if(c == 0x5a)
+			recognized++;
+		else
+			recognized = 0;
+	}
+}
+
+static void send_sync(void)
+{
+	send_int(0x5a5a5a5a);
+}
+
+int ident_and_download_kernel(void *buffer, int maxlength)
+{
+	int length;
+	unsigned int crc;
+	int i;
+	char msgtype;
+	unsigned char *_buffer = buffer;
+
+	while(1) {
+		receive_sync();
+		msgtype = receive_char();
+		if(msgtype == MSGTYPE_REQUEST_IDENT) {
+			send_int(0x41524f52); /* "AROR" - ARTIQ runtime on OpenRISC */
+			send_int(1000000000000LL/identifier_frequency_read()); /* RTIO clock period in picoseconds */
+		} else if(msgtype == MSGTYPE_LOAD_KERNEL) {
+			length = receive_int();
+			if(length > maxlength) {
+				send_char(0x4c); /* Incorrect length */
+				return -1;
+			}
+			crc = receive_int();
+			for(i=0;i<length;i++)
+				_buffer[i] = receive_char();
+			if(crc32(buffer, length) != crc) {
+				send_char(0x43); /* CRC failed */
+				return -1;
+			}
+			send_char(0x4f); /* kernel reception OK */
+			return length;
+		} else
+			return -1;
+	}
+}
+
+int rpc(int rpc_num, int n_args, ...)
+{
+	send_sync();
+	send_char(MSGTYPE_RPC_REQUEST);
+	send_sint(rpc_num);
+	send_char(n_args);
+
+	va_list args;
+	va_start(args, n_args);
+	while(n_args--)
+		send_int(va_arg(args, int));
+	va_end(args);
+
+	return receive_int();
+}
+
+void kernel_finished(void)
+{
+	send_sync();
+	send_char(MSGTYPE_KERNEL_FINISHED);
+}
diff --git a/soc/runtime/dds.c b/soc/runtime/dds.c
new file mode 100644
index 000000000..122fed391
--- /dev/null
+++ b/soc/runtime/dds.c
@@ -0,0 +1,42 @@
+#include <hw/common.h>
+
+#include "dds.h"
+
+#define DDS_FTW0  0x0a
+#define DDS_FTW1  0x0b
+#define DDS_FTW2  0x0c
+#define DDS_FTW3  0x0d
+#define DDS_FUD   0x40
+#define DDS_GPIO  0x41
+
+#define DDS_READ(addr) \
+	MMPTR(0xb0000000 + (addr)*4)
+
+#define DDS_WRITE(addr, data) \
+	MMPTR(0xb0000000 + (addr)*4) = data
+
+void dds_init(void)
+{
+	int i;
+
+	DDS_WRITE(DDS_GPIO, 1 << 7);
+
+	for(i=0;i<8;i++) {
+		DDS_WRITE(DDS_GPIO, i);
+		DDS_WRITE(0x00, 0x78);
+		DDS_WRITE(0x01, 0x00);
+		DDS_WRITE(0x02, 0x00);
+		DDS_WRITE(0x03, 0x00);
+		DDS_WRITE(DDS_FUD, 0);
+	}
+}
+
+void dds_program(int channel, int ftw)
+{
+	DDS_WRITE(DDS_GPIO, channel);
+	DDS_WRITE(DDS_FTW0, ftw & 0xff);
+	DDS_WRITE(DDS_FTW1, (ftw >> 8) & 0xff);
+	DDS_WRITE(DDS_FTW2, (ftw >> 16) & 0xff);
+	DDS_WRITE(DDS_FTW3, (ftw >> 24) & 0xff);
+	DDS_WRITE(DDS_FUD, 0);
+}
diff --git a/soc/runtime/dds.h b/soc/runtime/dds.h
new file mode 100644
index 000000000..91093b03b
--- /dev/null
+++ b/soc/runtime/dds.h
@@ -0,0 +1,7 @@
+#ifndef __DDS_H
+#define __DDS_H
+
+void dds_init(void);
+void dds_program(int channel, int ftw);
+
+#endif /* __DDS_H */
diff --git a/soc/runtime/elf_loader.c b/soc/runtime/elf_loader.c
index f2518de83..718bec49a 100644
--- a/soc/runtime/elf_loader.c
+++ b/soc/runtime/elf_loader.c
@@ -89,7 +89,7 @@ struct elf32_sym {
 	SANITIZE_OFFSET_SIZE(offset, sizeof(target_type)); \
 	target = (target_type *)((char *)elf_data + offset)
 
-static void *find_symbol(const struct symbol *symbols, const char *name)
+void *find_symbol(const struct symbol *symbols, const char *name)
 {
 	int i;
 
@@ -117,7 +117,7 @@ static int fixup(void *dest, int dest_length, struct elf32_rela *rela, void *tar
 	return 1;
 }
 
-int load_elf(const struct symbol *symbols, void *elf_data, int elf_length, void *dest, int dest_length)
+int load_elf(symbol_resolver resolver, void *elf_data, int elf_length, void *dest, int dest_length)
 {
 	struct elf32_ehdr *ehdr;
 	struct elf32_shdr *strtable;
@@ -199,7 +199,7 @@ int load_elf(const struct symbol *symbols, void *elf_data, int elf_length, void
 			void *target;
 
 			name = (char *)elf_data + strtaboff + sym->name;
-			target = find_symbol(symbols, name);
+			target = resolver(name);
 			if(target == NULL) {
 				printf("Undefined symbol: %s\n", name);
 				return 0;
diff --git a/soc/runtime/elf_loader.h b/soc/runtime/elf_loader.h
index 7c8fae33d..5b8431ff8 100644
--- a/soc/runtime/elf_loader.h
+++ b/soc/runtime/elf_loader.h
@@ -6,6 +6,9 @@ struct symbol {
 	void *target;
 };
 
-int load_elf(const struct symbol *symbols, void *elf_data, int elf_length, void *dest, int dest_length);
+void *find_symbol(const struct symbol *symbols, const char *name);
+
+typedef void * (*symbol_resolver)(const char *name);
+int load_elf(symbol_resolver resolver, void *elf_data, int elf_length, void *dest, int dest_length);
 
 #endif /* __ELF_LOADER_H */
diff --git a/soc/runtime/gpio.c b/soc/runtime/gpio.c
new file mode 100644
index 000000000..3d7948ac4
--- /dev/null
+++ b/soc/runtime/gpio.c
@@ -0,0 +1,14 @@
+#include <generated/csr.h>
+
+#include "gpio.h"
+
+void gpio_set(int channel, int value)
+{
+	static int csr_value;
+
+	if(value)
+		csr_value |= 1 << channel;
+	else
+		csr_value &= ~(1 << channel);
+	leds_out_write(csr_value);
+}
diff --git a/soc/runtime/gpio.h b/soc/runtime/gpio.h
new file mode 100644
index 000000000..63301cca5
--- /dev/null
+++ b/soc/runtime/gpio.h
@@ -0,0 +1,6 @@
+#ifndef __GPIO_H
+#define __GPIO_H
+
+void gpio_set(int channel, int value);
+
+#endif /* __GPIO_H */
diff --git a/soc/runtime/main.c b/soc/runtime/main.c
index cf907c132..6aca21f55 100644
--- a/soc/runtime/main.c
+++ b/soc/runtime/main.c
@@ -1,208 +1,13 @@
 #include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <stdarg.h>
-#include <crc.h>
-
 #include <irq.h>
 #include <uart.h>
-#include <console.h>
 #include <system.h>
-#include <hw/common.h>
-#include <generated/csr.h>
 
+#include "corecom.h"
 #include "elf_loader.h"
-
-enum {
-	MSGTYPE_REQUEST_IDENT		= 0x01,
-	MSGTYPE_LOAD_KERNEL			= 0x02,
-	MSGTYPE_KERNEL_FINISHED		= 0x03,
-	MSGTYPE_RPC_REQUEST			= 0x04,
-};
-
-static int receive_int(void)
-{
-	unsigned int r;
-	int i;
-
-	r = 0;
-	for(i=0;i<4;i++) {
-		r <<= 8;
-		r |= (unsigned char)uart_read();
-	}
-	return r;
-}
-
-static char receive_char(void)
-{
-	return uart_read();
-}
-
-static void send_int(int x)
-{
-	int i;
-
-	for(i=0;i<4;i++) {
-		uart_write((x & 0xff000000) >> 24);
-		x <<= 8;
-	}
-}
-
-static void send_sint(short int i)
-{
-	uart_write((i >> 8) & 0xff);
-	uart_write(i & 0xff);
-}
-
-static void send_char(char c)
-{
-	uart_write(c);
-}
-
-static void receive_sync(void)
-{
-	char c;
-	int recognized;
-
-	recognized = 0;
-	while(recognized < 4) {
-		c = uart_read();
-		if(c == 0x5a)
-			recognized++;
-		else
-			recognized = 0;
-	}
-}
-
-static void send_sync(void)
-{
-	send_int(0x5a5a5a5a);
-}
-
-static int ident_and_download_kernel(void *buffer, int maxlength)
-{
-	int length;
-	unsigned int crc;
-	int i;
-	char msgtype;
-	unsigned char *_buffer = buffer;
-
-	while(1) {
-		receive_sync();
-		msgtype = receive_char();
-		if(msgtype == MSGTYPE_REQUEST_IDENT) {
-			send_int(0x41524f52); /* "AROR" - ARTIQ runtime on OpenRISC */
-			send_int(1000000000000LL/identifier_frequency_read()); /* RTIO clock period in picoseconds */
-		} else if(msgtype == MSGTYPE_LOAD_KERNEL) {
-			length = receive_int();
-			if(length > maxlength) {
-				send_char(0x4c); /* Incorrect length */
-				return -1;
-			}
-			crc = receive_int();
-			for(i=0;i<length;i++)
-				_buffer[i] = receive_char();
-			if(crc32(buffer, length) != crc) {
-				send_char(0x43); /* CRC failed */
-				return -1;
-			}
-			send_char(0x4f); /* kernel reception OK */
-			return length;
-		} else
-			return -1;
-	}
-}
-
-static int rpc(int rpc_num, int n_args, ...)
-{
-	send_sync();
-	send_char(MSGTYPE_RPC_REQUEST);
-	send_sint(rpc_num);
-	send_char(n_args);
-
-	va_list args;
-	va_start(args, n_args);
-	while(n_args--)
-		send_int(va_arg(args, int));
-	va_end(args);
-
-	return receive_int();
-}
-
-static void gpio_set(int channel, int value)
-{
-	static int csr_value;
-
-	if(value)
-		csr_value |= 1 << channel;
-	else
-		csr_value &= ~(1 << channel);
-	leds_out_write(csr_value);
-}
-
-static void rtio_set(long long int timestamp, int channel, int value)
-{
-	rtio_reset_write(0);
-	rtio_chan_sel_write(channel);
-	rtio_o_timestamp_write(timestamp);
-	rtio_o_value_write(value);
-	while(!rtio_o_writable_read());
-	rtio_o_we_write(1);
-}
-
-static void rtio_sync(int channel)
-{
-	rtio_chan_sel_write(channel);
-	while(rtio_o_level_read() != 0);
-}
-
-#define DDS_FTW0  0x0a
-#define DDS_FTW1  0x0b
-#define DDS_FTW2  0x0c
-#define DDS_FTW3  0x0d
-#define DDS_FUD   0x40
-#define DDS_GPIO  0x41
-
-#define DDS_READ(addr) \
-	MMPTR(0xb0000000 + (addr)*4)
-
-#define DDS_WRITE(addr, data) \
-	MMPTR(0xb0000000 + (addr)*4) = data
-
-static void dds_program(int channel, int ftw)
-{
-	DDS_WRITE(DDS_GPIO, channel);
-	DDS_WRITE(DDS_FTW0, ftw & 0xff);
-	DDS_WRITE(DDS_FTW1, (ftw >> 8) & 0xff);
-	DDS_WRITE(DDS_FTW2, (ftw >> 16) & 0xff);
-	DDS_WRITE(DDS_FTW3, (ftw >> 24) & 0xff);
-	DDS_WRITE(DDS_FUD, 0);
-}
-
-static const struct symbol syscalls[] = {
-	{"__syscall_rpc",			rpc},
-	{"__syscall_gpio_set",		gpio_set},
-	{"__syscall_rtio_set",		rtio_set},
-	{"__syscall_rtio_sync",		rtio_sync},
-	{"__syscall_dds_program",	dds_program},
-	{NULL, NULL}
-};
-
-static void dds_init(void)
-{
-	int i;
-
-	DDS_WRITE(DDS_GPIO, 1 << 7);
-
-	for(i=0;i<8;i++) {
-		DDS_WRITE(DDS_GPIO, i);
-		DDS_WRITE(0x00, 0x78);
-		DDS_WRITE(0x01, 0x00);
-		DDS_WRITE(0x02, 0x00);
-		DDS_WRITE(0x03, 0x00);
-		DDS_WRITE(DDS_FUD, 0);
-	}
-}
+#include "symbols.h"
+#include "rtio.h"
+#include "dds.h"
 
 typedef void (*kernel_function)(void);
 
@@ -222,16 +27,15 @@ int main(void)
 	while(1) {
 		length = ident_and_download_kernel(kbuf, sizeof(kbuf));
 		if(length > 0) {
-			if(load_elf(syscalls, kbuf, length, kcode, sizeof(kcode))) {
-				flush_cpu_icache();
+			if(load_elf(resolve_symbol, kbuf, length, kcode, sizeof(kcode))) {
+				rtio_init();
 				dds_init();
+				flush_cpu_icache();
 				k();
-				rtio_reset_write(1);
-				send_sync();
-				send_char(MSGTYPE_KERNEL_FINISHED);
+				kernel_finished();
 			}
 		}
 	}
-	
+
 	return 0;
 }
diff --git a/soc/runtime/rtio.c b/soc/runtime/rtio.c
new file mode 100644
index 000000000..f75aa2413
--- /dev/null
+++ b/soc/runtime/rtio.c
@@ -0,0 +1,24 @@
+#include <generated/csr.h>
+
+#include "rtio.h"
+
+void rtio_init(void)
+{
+	rtio_reset_write(1);
+}
+
+void rtio_set(long long int timestamp, int channel, int value)
+{
+	rtio_reset_write(0);
+	rtio_chan_sel_write(channel);
+	rtio_o_timestamp_write(timestamp);
+	rtio_o_value_write(value);
+	while(!rtio_o_writable_read());
+	rtio_o_we_write(1);
+}
+
+void rtio_sync(int channel)
+{
+	rtio_chan_sel_write(channel);
+	while(rtio_o_level_read() != 0);
+}
diff --git a/soc/runtime/rtio.h b/soc/runtime/rtio.h
new file mode 100644
index 000000000..2ed47058e
--- /dev/null
+++ b/soc/runtime/rtio.h
@@ -0,0 +1,8 @@
+#ifndef __RTIO_H
+#define __RTIO_H
+
+void rtio_init(void);
+void rtio_set(long long int timestamp, int channel, int value);
+void rtio_sync(int channel);
+
+#endif /* __RTIO_H */
diff --git a/soc/runtime/symbols.c b/soc/runtime/symbols.c
new file mode 100644
index 000000000..a00fe0d5c
--- /dev/null
+++ b/soc/runtime/symbols.c
@@ -0,0 +1,41 @@
+#include <string.h>
+
+#include "elf_loader.h"
+#include "corecom.h"
+#include "gpio.h"
+#include "rtio.h"
+#include "dds.h"
+#include "symbols.h"
+
+static const struct symbol syscalls[] = {
+	{"rpc",				rpc},
+	{"gpio_set",		gpio_set},
+	{"rtio_set",		rtio_set},
+	{"rtio_sync",		rtio_sync},
+	{"dds_program",		dds_program},
+	{NULL, NULL}
+};
+
+static long long int gcd64(long long int a, long long int b)
+{
+	long long int c;
+
+	while(a) {
+		c = a;
+		a = b % a;
+		b = c;
+	}
+	return b;
+}
+
+static const struct symbol arithmetic[] = {
+	{"__gcd64",			gcd64},
+	{NULL, NULL}
+};
+
+void *resolve_symbol(const char *name)
+{
+	if(strncmp(name, "__syscall_", 10) == 0)
+		return find_symbol(syscalls, name + 10);
+	return find_symbol(arithmetic, name);
+}
diff --git a/soc/runtime/symbols.h b/soc/runtime/symbols.h
new file mode 100644
index 000000000..c963a1e7d
--- /dev/null
+++ b/soc/runtime/symbols.h
@@ -0,0 +1,6 @@
+#ifndef __SYMBOLS_H
+#define __SYMBOLS_H
+
+void *resolve_symbol(const char *name);
+
+#endif /* __SYMBOLS_H */