From 61df5113a25b7ce5a057eb6fd2e1e940199b07f0 Mon Sep 17 00:00:00 2001
From: morgan <mc@m-labs.hk>
Date: Wed, 9 Oct 2024 10:56:24 +0800
Subject: [PATCH] proto fw: add error correction for 4x char

---
 src/libboard_artiq/src/cxp_proto.rs | 70 +++++++++++++++++------------
 1 file changed, 41 insertions(+), 29 deletions(-)

diff --git a/src/libboard_artiq/src/cxp_proto.rs b/src/libboard_artiq/src/cxp_proto.rs
index 5ac366d..e3d8ae5 100644
--- a/src/libboard_artiq/src/cxp_proto.rs
+++ b/src/libboard_artiq/src/cxp_proto.rs
@@ -36,6 +36,14 @@ fn get_cxp_crc(bytes: &[u8]) -> u32 {
 }
 
 trait CxpRead {
+    fn read_u8(&mut self) -> Result<u8, Error>;
+
+    fn read_u16(&mut self) -> Result<u16, Error>;
+
+    fn read_u32(&mut self) -> Result<u32, Error>;
+
+    fn read_u64(&mut self) -> Result<u64, Error>;
+
     fn read_exact_4x(&mut self, buf: &mut [u8]) -> Result<(), Error>;
 
     fn read_4x_u8(&mut self) -> Result<u8, Error>;
@@ -45,20 +53,42 @@ trait CxpRead {
     fn read_4x_u32(&mut self) -> Result<u32, Error>;
 
     fn read_4x_u64(&mut self) -> Result<u64, Error>;
-
-    fn read_u16(&mut self) -> Result<u16, Error>;
-
-    fn read_u32(&mut self) -> Result<u32, Error>;
-
-    fn read_u64(&mut self) -> Result<u64, Error>;
 }
 impl<Cursor: Read> CxpRead for Cursor {
+    fn read_u8(&mut self) -> Result<u8, Error> {
+        let mut bytes = [0; 1];
+        self.read_exact(&mut bytes)?;
+        Ok(bytes[0])
+    }
+
+    fn read_u16(&mut self) -> Result<u16, Error> {
+        let mut bytes = [0; 2];
+        self.read_exact(&mut bytes)?;
+        Ok(NetworkEndian::read_u16(&bytes))
+    }
+
+    fn read_u32(&mut self) -> Result<u32, Error> {
+        let mut bytes = [0; 4];
+        self.read_exact(&mut bytes)?;
+        Ok(NetworkEndian::read_u32(&bytes))
+    }
+
+    fn read_u64(&mut self) -> Result<u64, Error> {
+        let mut bytes = [0; 8];
+        self.read_exact(&mut bytes)?;
+        Ok(NetworkEndian::read_u64(&bytes))
+    }
+
     fn read_exact_4x(&mut self, buf: &mut [u8]) -> Result<(), Error> {
-        for b in buf {
-            // TODO: add error correction
-            let mut bytes = [0; 4];
-            self.read_exact(&mut bytes)?;
-            *b = bytes[0];
+        for byte in buf {
+            // Section 9.2.2.1 (CXP-001-2021)
+            // decoder should immune to single bit errors when handling 4x duplicated characters
+            let a = self.read_u8()?;
+            let b = self.read_u8()?;
+            let c = self.read_u8()?;
+            let d = self.read_u8()?;
+            // vote and return majority
+            *byte = a & b & c | a & b & d | a & c & d | b & c & d;
         }
         Ok(())
     }
@@ -86,24 +116,6 @@ impl<Cursor: Read> CxpRead for Cursor {
         self.read_exact_4x(&mut bytes)?;
         Ok(NetworkEndian::read_u64(&bytes))
     }
-
-    fn read_u16(&mut self) -> Result<u16, Error> {
-        let mut bytes = [0; 2];
-        self.read_exact(&mut bytes)?;
-        Ok(NetworkEndian::read_u16(&bytes))
-    }
-
-    fn read_u32(&mut self) -> Result<u32, Error> {
-        let mut bytes = [0; 4];
-        self.read_exact(&mut bytes)?;
-        Ok(NetworkEndian::read_u32(&bytes))
-    }
-
-    fn read_u64(&mut self) -> Result<u64, Error> {
-        let mut bytes = [0; 8];
-        self.read_exact(&mut bytes)?;
-        Ok(NetworkEndian::read_u64(&bytes))
-    }
 }
 
 #[derive(Debug)]