/*
 *       ipv4_tx.v
 *
 *	 Copyright 2025 Private Island Networks Inc.
 *   Copyright 2018, 2019, 2020 Mind Chasers Inc.
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 *
 *	function: Layer 3 (and 4) Support for Controller Transmit
 *	
 *
 */

module ipv4_tx_c(
	input rstn,
	input phy_resetn,
	input clk,

	// Control Interface
	input cont_clk,			// controller clock
	input cont_sel,
	input cont_we,
	input [7:0] cont_addr,
	input [15:0] cont_d_i,
	output reg [15:0] cont_d_o,

	// Line State  
	input mode_100Mbit, 
	input phy_up,	

	// Switch I/F
	input [2:0] tx_mode,
	input [2:0] tx_src_sel,
	input [10:0] byte_cnt_i,

	// MAC Interface
	input fifo_re_i,
	output reg fifo_empty_o,
	output reg [8:0] fifo_d_o,
	
	// Debug
	output [7:0] gpio
);
	
`define INCLUDED
`include "ethernet_params.v"
`include "rgmii_params.v"
`undef INCLUDED

	localparam TX_CNT_OFFSET = 11'h15;	// offset for start of IP Header in Ethernet frame
	localparam TX_CNT_CKSUM_START = TX_CNT_OFFSET + 10;

	wire ipv4_hdr_active;
	reg [10:0] tx_cnt;
	reg [17:0] ipv4_cksum;
	reg [15:0] ipv4_pkt_length;
	reg [15:0] udp_pkt_length;
	integer i;
	
	assign ipv4_hdr_active = (tx_mode == TX_MODE_XMT_CUSTOM && tx_src_sel == TX_SRC_SEL_UC);

	always @(posedge clk, negedge rstn)
		if ( !rstn )
			tx_cnt <= 11'd0;
		else if (ipv4_hdr_active)
			tx_cnt <= tx_cnt + 1'b1;
		else 
			tx_cnt <= 11'd0;
			
			
	always @(posedge clk, negedge rstn)
		if ( !rstn ) begin
			ipv4_pkt_length <= 16'd0;
			udp_pkt_length <= 16'd0;
		end
		else if (ipv4_hdr_active && tx_cnt == 11'd0) begin
			ipv4_pkt_length <= byte_cnt_i + SZ_IPV4_HEADER + SZ_UDP_HEADER;
			udp_pkt_length <= byte_cnt_i + SZ_UDP_HEADER;
		end
			
	always @(posedge clk, negedge rstn)
		if ( !rstn )
			ipv4_cksum <= 18'd0;
		else if (!ipv4_hdr_active)
			ipv4_cksum <= 18'd0;
		else if (tx_cnt < 11'd20 && tx_cnt[0])
			ipv4_cksum <= ipv4_cksum + (ipv4_hdr(tx_cnt-1)<<8) + ipv4_hdr(tx_cnt);
		// else if (tx_cnt == 11'd20)
		//	ipv4_cksum <= ipv4_cksum + ipv4_pkt_length;
		else if (tx_cnt == 11'd21)
			ipv4_cksum <= {2'b00,ipv4_cksum[15:0]} + {16'h0000,ipv4_cksum[17:16]};
		else if (tx_cnt == 11'd22)
			ipv4_cksum <= {2'b00, ~ipv4_cksum[15:0]};	
			
	// fifo_empty_o	
	always @(posedge clk, negedge rstn)
		if ( !rstn )	
			fifo_empty_o <= 1'b1;
		else if (tx_cnt >= TX_CNT_OFFSET && tx_cnt < (TX_CNT_OFFSET + SZ_IPV4_HEADER + SZ_UDP_HEADER))
			fifo_empty_o <= 1'b0;
		else
			fifo_empty_o <= 1'b1;
			
	// fifo_d_o
	always @(posedge clk, negedge rstn)
		if ( !rstn )	
			fifo_d_o <= 9'h000;
		else if (tx_cnt == TX_CNT_CKSUM_START)
			fifo_d_o <= ipv4_cksum[15:8];
		else if (tx_cnt == TX_CNT_CKSUM_START+1)
			fifo_d_o <= ipv4_cksum[7:0];
		else if (tx_cnt >= TX_CNT_OFFSET && tx_cnt < TX_CNT_OFFSET + SZ_IPV4_HEADER)
			fifo_d_o <= ipv4_hdr(tx_cnt-TX_CNT_OFFSET);
		else if (tx_cnt >= TX_CNT_OFFSET && tx_cnt < TX_CNT_OFFSET + SZ_IPV4_HEADER + SZ_UDP_HEADER)
			fifo_d_o <= udp_hdr(tx_cnt-(TX_CNT_OFFSET + SZ_IPV4_HEADER));
		else
			fifo_d_o <= 9'h000;		
			
			
	// generate the IPv4 header
	// Assuming the header is only 20 bytes, this is both efficient and flexible
	function automatic [7:0] ipv4_hdr;
		input [10:0] ad;
		case(ad)
			0: ipv4_hdr = 8'h45;	// Version
			1: ipv4_hdr = 8'h00;	// IHL
			2: ipv4_hdr = ipv4_pkt_length[15:8];	// Total Length
			3: ipv4_hdr = ipv4_pkt_length[7:0];
			4: ipv4_hdr = 8'h54;
			5: ipv4_hdr = 8'hDB;
			6: ipv4_hdr = 8'h40;
			7: ipv4_hdr = 8'h00;
			8: ipv4_hdr = 8'h40;	// TTL
			9: ipv4_hdr = 8'h11;	// L4 Protocol (UDP=0x11)
			10: ipv4_hdr = 8'h00;	// Checksum
			11: ipv4_hdr = 8'h00;
			12: ipv4_hdr = 8'd192;	// IP Source Address
			13: ipv4_hdr = 8'd168;
			14: ipv4_hdr = 8'd5;
			15: ipv4_hdr = 8'd100;
			16: ipv4_hdr = 8'd192;	// IP Destination Address
			17: ipv4_hdr = 8'd168;
			18: ipv4_hdr = 8'd5;
			19: ipv4_hdr = 8'd40;			
			default: ipv4_hdr = 8'h00;
		endcase
	endfunction
	
	
	// generate the UDP header
	function automatic [7:0] udp_hdr;
		input [10:0] ad;
		case(ad)
			0: udp_hdr = 8'h80;	// SRC Port
			1: udp_hdr = 8'h00;	// 
			2: udp_hdr = 8'h80;	// DST Port
			3: udp_hdr = 8'h00;
			4: udp_hdr = udp_pkt_length[15:8];	// Length
			5: udp_hdr = udp_pkt_length[7:0];
			6: udp_hdr = 8'h00;					//Checksum
			7: udp_hdr = 8'h00;		
			default: udp_hdr = 8'h00;
		endcase
	endfunction
	
	assign gpio[0] = |ipv4_cksum[7:0];
	assign gpio[1] = |ipv4_cksum[15:8];

endmodule