Cosmos/source/Cosmos.Driver.RTL8139/PacketHeader.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace Cosmos.Driver.RTL8139
{
    /// <summary>
    /// The packethead consists of two bytes (i.e. 16 bits).
    /// A PacketHead contains information about a network Packet, and its transfer.
    /// </summary>
    public class PacketHeader
    {
        private UInt16 head;

        public PacketHeader(UInt16 data)
        {
            head = data;
        }

        public ushort PacketLength 
        { 
            get {return 2048;} //TODO: Get from packet?
            //private set; 
        }

        public bool IsReceiveOk()
        {
            return CheckBit(PacketHeadBit.ROK);
        }

        public bool IsFrameAlignmentError()
        {
            return CheckBit(PacketHeadBit.FAE);
        }

        public bool IsCRCError()
        {
            return CheckBit(PacketHeadBit.CRC);
        }

        public bool IsLongPacket()
        {
            return CheckBit(PacketHeadBit.LONG);
        }

        public bool IsRuntPacket()
        {
            return CheckBit(PacketHeadBit.RUNT);
        }

        public bool IsInvalidSymbolError()
        {
            return CheckBit(PacketHeadBit.ISE);
        }

        public bool IsBroadcastAddress()
        {
            return CheckBit(PacketHeadBit.BAR);
        }

        public bool IsPhysicalAddressMatch()
        {
            return CheckBit(PacketHeadBit.PAM);
        }

        public bool IsMulticastAddress()
        {
            return CheckBit(PacketHeadBit.MAR);
        }

        /// <summary>
        /// Bitwise checks it the given bit is set in the PacketHeader.
        /// </summary>
        /// <param name="bit">The zero-based position of a bit in the head. I.e. bit 1 is the second bit.</param>
        /// <returns>Returns TRUE if bit is set in packetheader</returns>
        private bool CheckBit(PacketHeadBit bit)
        {
            //A single bit is LEFT SHIFTED the number a given number of bits.
            //and bitwise AND'ed together with the packethead.
            //So the initial value is   :       0000 0000.
            //Left shifting a bit 3 bits:       0000 0100
            //And'ed together with the head:    0101 0101 AND 0000 01000 => 0000 0100 (which is greater than zero - so bit is set).
            
            ushort mask = (ushort)(1 << (ushort)bit);
            return (head & mask) != 0;
        }

        private enum PacketHeadBit : byte
        {
            ROK = 0x00, //Receive OK
            FAE = 0x01, //Frame Alignment Error
            CRC = 0x02, //CRC Error
            LONG = 0x03,//Long packet - set to 1 when packet over 4k bytes
            RUNT = 0x04,//Runt packet received (smaller than 64 bytes)
            ISE = 0x05, //Invalid Symbol Error (Only 100BASE-TX).
            BAR = 0x0D, //Broadcast Address Received
            PAM = 0x0E, //Physical Address Matched
            MAR = 0x0F  //Multicast Address Received
        }
    }
}