From 91ca9fbcad041b5e863be925c56fbeb7c21b1b64 Mon Sep 17 00:00:00 2001
From: Robert Jordens <rj@m-labs.hk>
Date: Tue, 4 Jul 2017 16:49:59 +0200
Subject: [PATCH] sawg: also give offset some headroom

closes #771
---
 artiq/coredevice/sawg.py                | 8 ++++----
 artiq/gateware/test/dsp/test_sawg_fe.py | 3 +--
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/artiq/coredevice/sawg.py b/artiq/coredevice/sawg.py
index 4ea97e23f..c781c93de 100644
--- a/artiq/coredevice/sawg.py
+++ b/artiq/coredevice/sawg.py
@@ -281,18 +281,18 @@ class SAWG:
         width = 16
         time_width = 16
         cordic_gain = 1.646760258057163  # Cordic(width=16, guard=None).gain
-        cordic_gain *= 1.01  # leave a bit of headroom
+        head_room = 1.001
         self.config = Config(channel_base, self.core, cordic_gain)
         self.offset = Spline(width, time_width, channel_base + 1,
-                             self.core, 2.)
+                             self.core, 2.*head_room)
         self.amplitude1 = Spline(width, time_width, channel_base + 2,
-                                 self.core, 2*cordic_gain**2)
+                                 self.core, 2*head_room*cordic_gain**2)
         self.frequency1 = Spline(3*width, time_width, channel_base + 3,
                                  self.core, 1/self.core.coarse_ref_period)
         self.phase1 = Spline(width, time_width, channel_base + 4,
                              self.core, 1.)
         self.amplitude2 = Spline(width, time_width, channel_base + 5,
-                                 self.core, 2*cordic_gain**2)
+                                 self.core, 2*head_room*cordic_gain**2)
         self.frequency2 = Spline(3*width, time_width, channel_base + 6,
                                  self.core, 1/self.core.coarse_ref_period)
         self.phase2 = Spline(width, time_width, channel_base + 7,
diff --git a/artiq/gateware/test/dsp/test_sawg_fe.py b/artiq/gateware/test/dsp/test_sawg_fe.py
index b905fea37..5aa3e1241 100644
--- a/artiq/gateware/test/dsp/test_sawg_fe.py
+++ b/artiq/gateware/test/dsp/test_sawg_fe.py
@@ -68,8 +68,7 @@ class SAWGTest(unittest.TestCase):
         v = int(round((1 << 48) * .1 * self.t))
         self.assertEqual(
             self.rtio_manager.outputs, [
-                (0., 1, 0, int(round(
-                    (1 << self.driver.offset.width - 1)*.9))),
+                (0., 1, 0, int(round(self.driver.offset.scale*.9))),
                 (2.*self.t, 8, 0, int(round(
                     (1 << self.driver.frequency0.width) *
                     self.t/self.channel.parallelism*.1))),