From b631c1fa4afb6f11d54489ae14d6fb3521c2a5ae Mon Sep 17 00:00:00 2001
From: linuswck <linuswck@m-labs.hk>
Date: Wed, 11 Dec 2024 14:49:05 +0800
Subject: [PATCH] pid: add pipeline on error signal computation

---
 fast-servo/pid_err_sig_pipeline.patch | 19 +++++++++++++++++++
 flake.nix                             |  1 +
 2 files changed, 20 insertions(+)
 create mode 100644 fast-servo/pid_err_sig_pipeline.patch

diff --git a/fast-servo/pid_err_sig_pipeline.patch b/fast-servo/pid_err_sig_pipeline.patch
new file mode 100644
index 0000000..4e09e27
--- /dev/null
+++ b/fast-servo/pid_err_sig_pipeline.patch
@@ -0,0 +1,19 @@
+diff --git a/gateware/logic/pid.py b/gateware/logic/pid.py
+index e737577..f1a4096 100644
+--- a/gateware/logic/pid.py
++++ b/gateware/logic/pid.py
+@@ -43,10 +43,12 @@ class PID(Module, AutoCSR):
+         self.comb += [setpoint_signed.eq(self.setpoint.storage)]
+ 
+         self.error = Signal((self.width + 1, True))
++        error_reg = Signal((self.width + 1, True))
++        self.sync += self.error.eq(error_reg)
+ 
+         self.comb += [
+-            If(self.running, self.error.eq(self.input - self.setpoint.storage)).Else(
+-                self.error.eq(0)
++            If(self.running, error_reg.eq(self.input - self.setpoint.storage)).Else(
++                error_reg.eq(0)
+             )
+         ]
+ 
diff --git a/flake.nix b/flake.nix
index f3d89b0..80c0b46 100644
--- a/flake.nix
+++ b/flake.nix
@@ -169,6 +169,7 @@
           fast-servo/iir_pipeline.patch
           fast-servo/linien_module_pipeline.patch
           fast-servo/pid_pipeline.patch
+          fast-servo/pid_err_sig_pipeline.patch
         ];
         nativeBuildInputs = [
           (pkgs.python3.withPackages(ps: [