runtime: support arbitrarily long initial DDS setup time

artiq/devices/runtime.py

@@ -73,7 +73,7 @@ class LinkInterface:
 class Environment(LinkInterface):
     def __init__(self, ref_period):
         self.ref_period = ref_period
-        self.initial_time = 10000
+        self.initial_time = 2000
 
     def emit_object(self):
         tm = lt.TargetMachine.new(triple="or1k", cpu="generic")

soc/runtime/dds.c

@@ -18,9 +18,19 @@
 
 #define RTIO_FUD_CHANNEL 4
 
+static void fud_sync(void)
+{
+    rtio_chan_sel_write(RTIO_FUD_CHANNEL);
+    while(rtio_o_level_read() != 0);
+}
+
 static void fud(long long int fud_time)
 {
+    int r;
+
+    r = rtio_reset_read();
     rtio_reset_write(0);
+
     rtio_chan_sel_write(RTIO_FUD_CHANNEL);
     if(fud_time < 0) {
         rtio_counter_update_write(1);
@@ -32,12 +42,11 @@ static void fud(long long int fud_time)
     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);
+    if(r) {
+        fud_sync();
+        rtio_reset_write(1);
+    }
 }
 
 void dds_init(void)

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) {
-                dds_init();
                 rtio_init();
+                dds_init();
                 flush_cpu_icache();
                 k();
                 kernel_finished();