got it so that reading usb packets reliably works "sometimes"
diff --git a/aos/common/sensors/sensor_receiver-tmpl.h b/aos/common/sensors/sensor_receiver-tmpl.h
index dc9f17d..e3840c4 100644
--- a/aos/common/sensors/sensor_receiver-tmpl.h
+++ b/aos/common/sensors/sensor_receiver-tmpl.h
@@ -6,7 +6,7 @@
 
 template<class Values>
 const time::Time SensorReceiver<Values>::kJitterDelay =
-    time::Time::InSeconds(0.0035);
+    time::Time::InSeconds(0.00225);
 // Not a multiple of kSensorSendFrequency to unwedge ourself if we hit some bug
 // where it needs to get off of that frequency to work.
 template<class Values>
@@ -185,6 +185,7 @@
         }
       }
 
+      Synchronized(goal_time + kLoopFrequency * kTestCycles);
       return true;
     }
 
@@ -197,13 +198,6 @@
   int old_count = data_.count;
   DoReceiveData();
 
-  data_.checksum = ntoh(data_.checksum);
-  if (!data_.CheckChecksum()) {
-    LOG(WARNING, "got a bad packet\n");
-    return ReceiveData();
-  }
-
-  data_.NetworkToHost();
   if (data_.count < 0) {
     LOG(FATAL, "data count overflowed. currently %"PRId32"\n", data_.count);
   }
@@ -251,6 +245,13 @@
   while (true) {
     if (socket_.Receive(this->data(), sizeof(*this->data())) ==
         sizeof(*this->data())) {
+      this->data()->checksum = ntoh(this->data()->checksum);
+      if (!this->data()->CheckChecksum()) {
+        LOG(WARNING, "got a bad packet\n");
+        continue;
+      }
+
+      this->data()->NetworkToHost();
       return;
     }
     LOG(WARNING, "received incorrect amount of data\n");
diff --git a/aos/common/sensors/sensor_receiver.h b/aos/common/sensors/sensor_receiver.h
index c829d53..9cd24e1 100644
--- a/aos/common/sensors/sensor_receiver.h
+++ b/aos/common/sensors/sensor_receiver.h
@@ -53,6 +53,8 @@
 
   // Subclasses need to implement this to read 1 set of data (blocking until it
   // is available) into data().
+  // It needs to have the correct byte order etc and not be corrupted
+  // (subclasses can check the checksum if they want).
   virtual void DoReceiveData() = 0;
 
   // Optional: if subclasses can do anything to reinitialize after there are
@@ -60,6 +62,10 @@
   // This will be called right before calling DoReceiveData() the first time.
   virtual void Reset() {}
 
+  // Optional: if subclasses want to be notified when this is first convinced
+  // that it has a good packet, they should do whatever here.
+  virtual void Synchronized(time::Time /*last_packet_ideal_time*/) {}
+
   // Returns whether the current packet looks like a good one to use.
   bool GoodPacket();
 
diff --git a/aos/common/time.cc b/aos/common/time.cc
index 995011a..75ea196 100644
--- a/aos/common/time.cc
+++ b/aos/common/time.cc
@@ -120,6 +120,9 @@
 const Time Time::operator/(int32_t rhs) const {
   return Time(*this) /= rhs;
 }
+double Time::operator/(const Time &rhs) const {
+  return ToSeconds() / rhs.ToSeconds();
+}
 Time &Time::operator%=(int32_t rhs) {
   nsec_ = ToNSec() % rhs;
   const int wraps = nsec_ / kNSecInSec;
diff --git a/aos/common/time.h b/aos/common/time.h
index ea703f7..276cf1c 100644
--- a/aos/common/time.h
+++ b/aos/common/time.h
@@ -160,6 +160,8 @@
   const Time operator-(const Time &rhs) const;
   const Time operator*(int32_t rhs) const;
   const Time operator/(int32_t rhs) const;
+  // TODO(brians) test this
+  double operator/(const Time &rhs) const;
   const Time operator%(int32_t rhs) const;
 
   bool operator==(const Time &rhs) const;