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`timescale 1ns / 1ps

////////////////////////////////////////////////////////////////////////////////

// Company: 

// Engineer:

//

// Create Date:    21:23:10 11/21/05

// Design Name:    

// Module Name:    rxLenTypChecker

// Project Name:   

// Target Device:  

// Tool versions:  

// Description:

//

// Dependencies:

// 

// Revision:

// Revision 0.01 - File Created

// Additional Comments: Length/Type:

// 1. <64:  Length, we should remove PAD

// 2. >=64, <= 1518:    Length, valid frame, we don't need remove PAD(0x2E, 0x5DC)

// 3. >=1518: <9k+18: Length, jumbo frame, if supported (0x5DC, 0x2400)

//      4. >9k+18, = 0x8100: Type, Tagged frame

// 5. >9k+18, = 0x8808: Type, pause frame

// |<------------------------------ Data Field ---------------------------->|

// |<------------- True Data Field --------------> <-----Padded bits------->|

// |____________________________|_________________|

// |                                                    |                               |

// |     small_integer_cnt * 64   | small_bits_more |  

// |____________________________|_________________|____

// |___________________________________________________|_____________________

// |                                                                       |                                      |

// |                 integer_cnt * 64                    |       bits_more    |

// |___________________________________________________|____________________|

////////////////////////////////////////////////////////////////////////////////

module rxLenTypChecker(lt_data, tagged_len, jumbo_enable, tagged_frame, pause_frame, small_frame,

                       len_invalid, integer_cnt, small_integer_cnt, bits_more, inband_fcs,

                                                          small_bits_more, vlan_enable );

         input[15:0]  lt_data;       //Length or Type field of a frame

         input[15:0]  tagged_len;   //Actual length carried with tagged frame  

    input        jumbo_enable; //Enable jumbo frame recieving

         input        inband_fcs;        //In-band FCS

         input        vlan_enable;  //VLAN mode enable bit

         output       pause_frame;       //Indicate that current frame is a pause frame (a kind of control frame)       

         output       small_frame;

         output       len_invalid;       //Indicate that current frame is not an valid frame

         output[12:0] integer_cnt;        //number of 64bits DATA field contains

         output[12:0] small_integer_cnt; //number of 64bits real DATA field contains(without pad part)

         output       tagged_frame;      //number of 64bits DATA field of tagged frame contains

         output[2:0]  bits_more;  //number that is less than 64bits(whole data field)

         output[2:0]  small_bits_more; //number that is less than 64bits(unpadded data field) 

    wire[15:0]   current_len;

         wire[15:0]   current_cnt;

         wire         small_frame;

         wire         tagged_frame;

         parameter TP =1 ;

         assign current_len = tagged_frame?(tagged_len+2):(lt_data-2);   //Data field length

         assign current_cnt = current_len >> 3; //the number of 64bits data field has

         assign padded_frame = (current_len[15:6]==0) & (~current_len[5] | (current_len[5] & ~current_len[4]));

         assign small_frame = padded_frame & ~inband_fcs;  //padded frame

         assign bits_more = padded_frame? 4 :current_len[2:0];   // bits that is not 64bits enough

         assign small_bits_more = current_len[2:0];// for situation smaller than 64

         assign integer_cnt = padded_frame? 5 :current_cnt[12:0];

         assign small_integer_cnt = current_cnt[12:0];

         assign tagged_frame = (lt_data==16'h8100) & vlan_enable;

         assign pause_frame = (lt_data==16'h8808);

         assign len_invalid = ((~jumbo_enable & (lt_data > 1500)) & ~(tagged_frame|pause_frame)) | (~vlan_enable & tagged_frame);

         //not a large frame(except LT is type interpretion) when jumbo is not enabled, not a tagged frame when vlan is not enbaled

endmodule