C#

struct ... {
    ...
    [MarshalAs(UnmanagedType.ByValArray, SizeConst=1024)]
    byte[] byteArray;
    ...
}

using System.Runtime.InteropServices;

/*
typedef enum packetCmds_enum {
PC_TO_DSP_WRITE = 1,
PC_TO_DSP_READ = 2,
DSP_TO_PC_ACK = 3
}packetCmds_enum;
*/
public enum PacketCmds
{
    PC_TO_DSP_WRITE = 1,
    PC_TO_DSP_READ = 2,
    DSP_TO_PC_ACK = 3
}

/*
typedef struct cmdPacket_type {
packetCmds_enum cmd; //< Should be 32 bits
Uint32 size; //< Set to zero if no data
Uint32 addr; //< Target address
Uint8 data[MAX_PACKET_PAYLOAD];
Uint32 checksum; //< Includes cmd, size, addr and data.
} cmdPacket_type;
*/
[StructLayout(LayoutKind.Sequential)]
public struct CmdPacketType
{
    // #define MAX_PACKET_PAYLOAD 1024
    public const int MAX_PACKET_PAYLOAD = 1024;

    public PacketCmds cmd;
    public uint size;
    public uint addr;
    [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=MAX_PACKET_PAYLOAD)]
    public byte[] data;
    public uint checksum;
}