diff --git a/src/libboard_artiq/src/cxp_proto.rs b/src/libboard_artiq/src/cxp_proto.rs
index 64fc357..69223a3 100644
--- a/src/libboard_artiq/src/cxp_proto.rs
+++ b/src/libboard_artiq/src/cxp_proto.rs
@@ -16,16 +16,32 @@ const MEM_LEN: usize = 0x200;
 #[derive(Debug)]
 pub enum Error {
     BufferError,
+    CorruptedPacket,
+    CtrlAckError(u8),
     LinkDown,
     UnknownPacket(u8),
 }
 
+#[derive(Debug)]
+pub enum CtrlError {
+    AddressReadOnly,
+    AddressWriteOnly,
+    CRCFailed,
+    DataSizeDifferent,
+    InvalidAddress,
+    InvalidData,
+    InvalidOpcode,
+    MalformedPacket,
+    SizeToolarge,
+}
+
 impl From<IoError> for Error {
     fn from(_: IoError) -> Error {
         Error::BufferError
     }
 }
 
+#[derive(Debug)]
 pub enum Packet {
     // Upconn packet
     CtrlRead {
@@ -56,13 +72,13 @@ pub enum Packet {
     // Downconn packet
     CtrlAck {
         ackcode: u8,
-        length: u8,
+        length: u32,
         data: [u8; DATA_MAXSIZE],
     },
     CtrlAckWithTag {
         tag: u8,
         ackcode: u8,
-        length: u8,
+        length: u32,
         data: [u8; DATA_MAXSIZE],
     },
     CtrlAckNoData {
@@ -88,18 +104,26 @@ fn read_word(reader: &mut Cursor<&mut [u8]>) -> Result<u32, Error> {
 }
 
 impl Packet {
-    pub fn read_from(reader: &mut Cursor<&mut [u8]>, packet_type: u8) -> Result<(), Error> {
+    pub fn read_from(reader: &mut Cursor<&mut [u8]>, packet_type: u8) -> Result<Self, Error> {
         match packet_type {
             0x03 => {
-                let ackcode4x = read_word(reader);
-                println!("ackcode4x = {:#010X}", ackcode4x.unwrap());
-                let len = read_word(reader);
-                println!("len = {:#010X}", len.unwrap());
+                let ackcode: u8 = (read_word(reader)? & 0xFF) as u8;
+                let length = read_word(reader)?;
+
+                let mut data: [u8; DATA_MAXSIZE] = [0; DATA_MAXSIZE];
+                if ackcode == 0x00 || ackcode == 0x04 {
+                    reader.read(&mut data[0..length as usize])?;
+                };
+
+                match ackcode {
+                    0x00 | 0x04 => return Ok(Packet::CtrlAck { ackcode, length, data }),
+                    0x01 => return Ok(Packet::CtrlAckNoData { ackcode }),
+                    _ => return Err(Error::CtrlAckError(ackcode)),
+                }
             }
-            0x06 => {}
-            _ => {}
+            0x06 => return Err(Error::UnknownPacket(packet_type)),
+            _ => return Err(Error::UnknownPacket(packet_type)),
         }
-        Ok(())
     }
     pub fn write_to(&self, writer: &mut Cursor<&mut [u8]>) -> Result<(), Error> {
         // CoaXpress use big endian
@@ -146,9 +170,12 @@ impl Packet {
                 if ackcode == 0x00 || ackcode == 0x04 {
                     writer.write(&[0x00, 0x00, 0x00, length])?;
                     writer.write(&data[0..length as usize])?;
-                    let checksum = crc32::checksum_ieee(&writer.get_ref()[4..writer.position()]);
-                    writer.write(&(!checksum).to_le_bytes())?;
                 }
+
+                print_packet(&writer.get_ref()[4..writer.position()]);
+
+                let checksum = crc32::checksum_ieee(&writer.get_ref()[4..writer.position()]);
+                writer.write(&(!checksum).to_le_bytes())?;
             }
             _ => return Err(Error::UnknownPacket(0)),
         }
@@ -177,9 +204,26 @@ pub fn receive(channel: usize) -> Result<(), Error> {
         let mut reader = Cursor::new(slice::from_raw_parts_mut(ptr as *mut u8, MEM_LEN));
         let packet_type = (CXP[channel].downconn_packet_type_read)();
 
-        Packet::read_from(&mut reader, packet_type);
+        let packet = Packet::read_from(&mut reader, packet_type)?;
+        println!("{:?}", packet);
 
-        // print_packet(slice::from_raw_parts_mut(ptr as *mut u8, MEM_LEN));
+        // Section 9.2.2.2 (CXP-001-2021)
+        // Only Control packet need CRC32 appended in the end of the packet
+        // CoaXpress use the polynomial of IEEE-802.3 (Ethernet) CRC but the checksum calculation is different
+        // Also, the calculation does not include the first 4 bytes of packet_type
+        if packet_type == 0x03 || packet_type == 0x06 {
+            let checksum_at = reader.position();
+            let checksum = (!crc::crc32::checksum_ieee(&reader.get_ref()[0..checksum_at])).swap_bytes();
+            println!("checksum location = {:#010X}", checksum_at);
+            println!("calculated checksum = {:#010X}", checksum);
+            println!("read checksum = {:#010X}", read_word(&mut reader)?);
+            reader.set_position(checksum_at);
+            if read_word(&mut reader)? != checksum {
+                return Err(Error::CorruptedPacket);
+            }
+        }
+
+        print_packet(slice::from_raw_parts_mut(ptr as *mut u8, MEM_LEN));
     }
     Ok(())
 }