sawg: reduce coefficient width

jordens · jordens · commit 18e3f58c22e5 · 2016-12-08T16:14:32.000+01:00
diff --git a/artiq/gateware/dsp/sawg.py b/artiq/gateware/dsp/sawg.py
@@ -146,9 +146,9 @@ def __init__(self, width=16, parallelism=4, widths=None, orders=None):
 
         self.submodules.a1 = a1 = SplineParallelDDS(widths, orders)
         self.submodules.a2 = a2 = SplineParallelDDS(widths, orders)
-        coeff = [[int(round((1 << 26) * ci)) for ci in c]
+        coeff = [[int(round((1 << 18)*ci)) for ci in c]
                  for c in halfgen4_cascade(parallelism, width=.4, order=8)]
-        hbf = [ParallelHBFUpsampler(coeff, width=width, shift=25)
+        hbf = [ParallelHBFUpsampler(coeff, width=width, shift=17)
                for i in range(2)]
         self.submodules.b = b = SplineParallelDUC(
             widths._replace(a=len(a1.xo[0]), f=widths.f - width), orders,
