diff --git a/artiq/devices/runtime.py b/artiq/devices/runtime.py
index 5f84fc52e..9e55002de 100644
--- a/artiq/devices/runtime.py
+++ b/artiq/devices/runtime.py
@@ -12,7 +12,7 @@ _syscalls = {
     "rtio_set": "Iii:n",
     "rtio_replace": "Iii:n",
     "rtio_sync": "i:n",
-    "dds_program": "ii:n",
+    "dds_program": "iiI:n",
 }
 
 _chr_to_type = {
diff --git a/soc/runtime/dds.c b/soc/runtime/dds.c
index 8cfeb08ce..08aae424d 100644
--- a/soc/runtime/dds.c
+++ b/soc/runtime/dds.c
@@ -1,4 +1,6 @@
+#include <generated/csr.h>
 #include <hw/common.h>
+#include <stdio.h>
 
 #include "dds.h"
 
@@ -6,7 +8,6 @@
 #define DDS_FTW1  0x0b
 #define DDS_FTW2  0x0c
 #define DDS_FTW3  0x0d
-#define DDS_FUD   0x40
 #define DDS_GPIO  0x41
 
 #define DDS_READ(addr) \
@@ -15,6 +16,30 @@
 #define DDS_WRITE(addr, data) \
     MMPTR(0xb0000000 + (addr)*4) = data
 
+#define RTIO_FUD_CHANNEL 4
+
+static void fud(long long int fud_time)
+{
+    rtio_reset_write(0);
+    rtio_chan_sel_write(RTIO_FUD_CHANNEL);
+    if(fud_time < 0) {
+        rtio_counter_update_write(1);
+        fud_time = rtio_counter_read() + 3000;
+    }
+    rtio_o_timestamp_write(fud_time);
+    rtio_o_value_write(1);
+    rtio_o_we_write(1);
+    rtio_o_timestamp_write(fud_time+3*8);
+    rtio_o_value_write(0);
+    rtio_o_we_write(1);
+}
+
+static void fud_sync(void)
+{
+    rtio_chan_sel_write(RTIO_FUD_CHANNEL);
+    while(rtio_o_level_read() != 0);
+}
+
 void dds_init(void)
 {
     int i;
@@ -26,16 +51,18 @@ void dds_init(void)
         DDS_WRITE(0x01, 0x00);
         DDS_WRITE(0x02, 0x00);
         DDS_WRITE(0x03, 0x00);
-        DDS_WRITE(DDS_FUD, 0);
+        fud(-1);
+        fud_sync();
     }
 }
 
-void dds_program(int channel, int ftw)
+void dds_program(int channel, int ftw, long long int fud_time)
 {
+    fud_sync();
     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);
+    fud(fud_time);
 }
diff --git a/soc/runtime/dds.h b/soc/runtime/dds.h
index 91093b03b..78fa4e307 100644
--- a/soc/runtime/dds.h
+++ b/soc/runtime/dds.h
@@ -2,6 +2,6 @@
 #define __DDS_H
 
 void dds_init(void);
-void dds_program(int channel, int ftw);
+void dds_program(int channel, int ftw, long long int fud_time);
 
 #endif /* __DDS_H */
diff --git a/soc/runtime/main.c b/soc/runtime/main.c
index 49ba853d2..8250bfcd4 100644
--- a/soc/runtime/main.c
+++ b/soc/runtime/main.c
@@ -29,8 +29,8 @@ int main(void)
         if(length > 0) {
             k = load_elf(resolve_symbol, "run", kbuf, length, kcode, sizeof(kcode));
             if(k != NULL) {
-                rtio_init();
                 dds_init();
+                rtio_init();
                 flush_cpu_icache();
                 k();
                 kernel_finished();