gateware: Add pipeline to Demodulation

- Fix timing violations at 125MHz sys frequency

fast-servo/linien-demodulate_add_pipeline.patch

@@ -0,0 +1,21 @@
+diff --git a/gateware/logic/modulate.py b/gateware/logic/modulate.py
+index c750306..ffba1b2 100644
+--- a/gateware/logic/modulate.py
++++ b/gateware/logic/modulate.py
+@@ -45,12 +45,14 @@ class Demodulate(Module, AutoCSR):
+             cordic_mode="rotate",
+             func_mode="circular",
+         )
+-        self.comb += [
++        self.sync += [
+             # cordic input
+             self.cordic.xi.eq(self.x),
+             self.cordic.zi.eq(
+                 ((self.phase * self.multiplier.storage) + self.delay.storage) << 1
+-            ),
++            )
++        ]
++        self.comb += [
+             # cordic output
+             self.i.eq(self.cordic.xo >> 1),
+             self.q.eq(self.cordic.yo >> 1),

flake.nix

@@ -40,6 +40,7 @@
             ./fast-servo/pid_pipeline.patch
             ./fast-servo/pid_err_sig_pipeline.patch
             ./fast-servo/linien-gateware-chain-pipeline.patch
+            ./fast-servo/linien-demodulate_add_pipeline.patch
           ];
       };