core: add underflow recovery function

artiq/coredevice/comm_dummy.py

@@ -7,6 +7,7 @@ from artiq.coredevice.runtime import LinkInterface
 class _RuntimeEnvironment(LinkInterface):
     def __init__(self, ref_period):
         self.ref_period = ref_period
+        self.initial_time = 0
 
     def emit_object(self):
         return str(self.llvm_module)

artiq/coredevice/core.py

@@ -11,6 +11,7 @@ from artiq.transforms.interleave import interleave
 from artiq.transforms.lower_time import lower_time
 from artiq.transforms.unparse import unparse
 from artiq.py2llvm import get_runtime_binary
+from artiq.language.core import *
 
 
 def _announce_unparse(label, node):
@@ -46,6 +47,7 @@ class Core:
             runtime_env = comm.get_runtime_env()
         self.runtime_env = runtime_env
         self.comm = comm
+        self.core = self
 
     def transform_stack(self, func_def, rpc_map, exception_map,
                         debug_unparse=_no_debug_unparse):
@@ -67,7 +69,7 @@ class Core:
         interleave(func_def)
         debug_unparse("interleave", func_def)
 
-        lower_time(func_def, getattr(self.runtime_env, "initial_time", 0))
+        lower_time(func_def, self.runtime_env.initial_time)
         debug_unparse("lower_time", func_def)
 
         remove_inter_assigns(func_def)
@@ -103,3 +105,8 @@ class Core:
         self.comm.load(binary)
         self.comm.run(func_def.name)
         self.comm.serve(rpc_map, exception_map)
+
+    @kernel
+    def recover_underflow(self):
+        t = syscall("rtio_get_counter") + self.runtime_env.initial_time
+        at(cycles_to_time(t))

artiq/coredevice/runtime.py

@@ -17,6 +17,7 @@ _syscalls = {
     "rtio_set": "Iii:n",
     "rtio_replace": "Iii:n",
     "rtio_sync": "i:n",
+    "rtio_get_counter": "n:I",
     "rtio_get": "i:I",
     "rtio_pileup_count": "i:i",
     "dds_phase_clear_en": "ib:n",
@@ -48,7 +49,7 @@ def _str_to_functype(s):
         if c == "+":
             type_args.append(lc.Type.int())
             var_arg_fixcount = n
-        else:
+        elif c != "n":
             type_args.append(_chr_to_type[c]())
     return (var_arg_fixcount,
             lc.Type.function(type_ret, type_args,

examples/pulse_performance.py

@@ -20,7 +20,7 @@ class PulsePerformance(AutoContext):
                     delay(cycles_to_time(T))
             except RTIOUnderflow:
                 T += 1
-                delay(1*ms)
+                self.core.recover_underflow()
             else:
                 print_min_period(int(cycles_to_time(2*T)/(1*ns)))
                 break

soc/runtime/services.c

@@ -15,6 +15,7 @@ static const struct symbol syscalls[] = {
     {"rtio_set", rtio_set},
     {"rtio_replace", rtio_replace},
     {"rtio_sync", rtio_sync},
+    {"rtio_get_counter", rtio_get_counter},
     {"rtio_get", rtio_get},
     {"rtio_pileup_count", rtio_pileup_count},
     {"dds_phase_clear_en", dds_phase_clear_en},