diff --git a/src/libboard_artiq/src/cxp_proto.rs b/src/libboard_artiq/src/cxp_proto.rs
index 3339077..10f9773 100644
--- a/src/libboard_artiq/src/cxp_proto.rs
+++ b/src/libboard_artiq/src/cxp_proto.rs
@@ -110,21 +110,12 @@ fn capture_ctrl_packet(reader: &mut Cursor<&mut [u8]>, with_tag: bool) -> Result
 #[derive(Debug)]
 pub enum UpConnPacket {
     CtrlRead {
+        tag: Option<u8>,
         addr: u32,
         length: u8,
     },
     CtrlWrite {
-        addr: u32,
-        length: u8,
-        data: [u8; DATA_MAXSIZE],
-    }, // max register size is 8 bytes
-    CtrlReadWithTag {
-        tag: u8,
-        addr: u32,
-        length: u8,
-    },
-    CtrlWriteWithTag {
-        tag: u8,
+        tag: Option<u8>,
         addr: u32,
         length: u8,
         data: [u8; DATA_MAXSIZE],
@@ -152,34 +143,47 @@ impl UpConnPacket {
     pub fn write_to(&self, writer: &mut Cursor<&mut [u8]>) -> Result<(), Error> {
         // CoaXpress use big endian
         match *self {
-            UpConnPacket::CtrlRead { addr, length } => {
-                writer.write(&[0x02; 4])?;
+            UpConnPacket::CtrlRead { tag, addr, length } => {
+                match tag {
+                    Some(t) => {
+                        writer.write(&[0x05; 4])?;
+                        writer.write(&[t; 4])?;
+                    }
+                    None => {
+                        writer.write(&[0x02; 4])?;
+                    }
+                }
                 writer.write(&[0x00, 0x00, 0x00, length])?;
                 writer.write(&addr.to_be_bytes())?;
+
+                // Section 9.6.2 (CXP-001-2021)
+                // only bytes after the first 4 are used in calculating the checksum
+                let checksum = get_cxp_crc(&writer.get_ref()[4..writer.position()]);
+                writer.write(&checksum.to_be_bytes())?;
             }
-            UpConnPacket::CtrlWrite { addr, length, data } => {
-                writer.write(&[0x02; 4])?;
-                writer.write(&[0x01, 0x00, 0x00, length])?;
-                writer.write(&addr.to_be_bytes())?;
-                writer.write(&data[0..length as usize])?;
-            }
-            UpConnPacket::CtrlReadWithTag { tag, addr, length } => {
-                writer.write(&[0x05; 4])?;
-                writer.write(&[tag; 4])?;
-                writer.write(&[0x00, 0x00, 0x00, length])?;
-                writer.write(&addr.to_be_bytes())?;
-            }
-            UpConnPacket::CtrlWriteWithTag {
+            UpConnPacket::CtrlWrite {
                 tag,
                 addr,
                 length,
                 data,
             } => {
-                writer.write(&[0x05; 4])?;
-                writer.write(&[tag; 4])?;
+                match tag {
+                    Some(t) => {
+                        writer.write(&[0x05; 4])?;
+                        writer.write(&[t; 4])?;
+                    }
+                    None => {
+                        writer.write(&[0x02; 4])?;
+                    }
+                }
                 writer.write(&[0x01, 0x00, 0x00, length])?;
                 writer.write(&addr.to_be_bytes())?;
                 writer.write(&data[0..length as usize])?;
+
+                // Section 9.6.2 (CXP-001-2021)
+                // only bytes after the first 4 are used in calculating the checksum
+                let checksum = get_cxp_crc(&writer.get_ref()[4..writer.position()]);
+                writer.write(&checksum.to_be_bytes())?;
             }
             UpConnPacket::EventAck { packet_tag } => {
                 writer.write(&[0x08; 4])?;
@@ -199,17 +203,6 @@ impl UpConnPacket {
             }
             _ => {}
         }
-        // Section 9.2.2.2 (CXP-001-2021)
-        // The crc calculation does not include the first 4 bytes of packet_type
-        match *self {
-            UpConnPacket::CtrlRead { .. }
-            | UpConnPacket::CtrlWrite { .. }
-            | UpConnPacket::CtrlReadWithTag { .. }
-            | UpConnPacket::CtrlWriteWithTag { .. } => {
-                writer.write(&get_cxp_crc(&writer.get_ref()[4..writer.position()]).to_be_bytes())?;
-            }
-            _ => {}
-        }
         Ok(())
     }
 }
@@ -270,12 +263,18 @@ fn send_test_packet(channel: usize) -> Result<(), Error> {
     Ok(())
 }
 
+//
+// DEBUG: use only
+//
+//
+//
 pub fn write_u32(channel: usize, addr: u32, data: u32) -> Result<(), Error> {
     let mut data_slice: [u8; DATA_MAXSIZE] = [0; DATA_MAXSIZE];
     data_slice[..4].clone_from_slice(&data.to_be_bytes());
     send(
         channel,
         &UpConnPacket::CtrlWrite {
+            tag: None,
             addr,
             length: 4,
             data: data_slice,
@@ -286,7 +285,14 @@ pub fn write_u32(channel: usize, addr: u32, data: u32) -> Result<(), Error> {
 }
 
 pub fn read_u32(channel: usize, addr: u32) -> Result<(), Error> {
-    send(channel, &UpConnPacket::CtrlRead { addr, length: 4 })?;
+    send(
+        channel,
+        &UpConnPacket::CtrlRead {
+            tag: None,
+            addr,
+            length: 4,
+        },
+    )?;
 
     Ok(())
 }
@@ -297,6 +303,7 @@ pub fn write_u64(channel: usize, addr: u32, data: u64) -> Result<(), Error> {
     send(
         channel,
         &UpConnPacket::CtrlWrite {
+            tag: None,
             addr,
             length: 8,
             data: data_slice,
@@ -306,11 +313,6 @@ pub fn write_u64(channel: usize, addr: u32, data: u64) -> Result<(), Error> {
     Ok(())
 }
 
-//
-// DEBUG: use only
-//
-//
-//
 pub fn print_packet(pak: &[u8]) {
     println!("pak = [");
     for i in 0..(pak.len() / 4) {