/*                                                                      
 Copyright 2020 Blue Liang, liangkangnan@163.com
                                                                         
 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.                                          
 */


// clk = 50MHz时对应的波特率分频系数
`define UART_BAUD_115200        32'h1B8

// 串口寄存器地址
`define UART_CTRL_REG           32'h30000000
`define UART_STATUS_REG         32'h30000004
`define UART_BAUD_REG           32'h30000008
`define UART_TX_REG             32'h3000000c
`define UART_RX_REG             32'h30000010

`define UART_TX_BUSY_FLAG       32'h1
`define UART_RX_OVER_FLAG       32'h2

// 第一个包的大小
`define UART_FIRST_PACKET_LEN   8'd131
// 其他包的大小(每次烧写的字节数)
`define UART_REMAIN_PACKET_LEN  8'd131

`define UART_RESP_ACK           32'h6
`define UART_RESP_NAK           32'h15

// 烧写起始地址
`define ROM_START_ADDR          32'h0


// 串口更新固件模块
module uart_debug(

    input wire clk,                // 时钟信号
    input wire rst,                // 复位信号

    input wire debug_en_i,         // 模块使能信号

    output wire req_o,
    output reg mem_we_o,
    output reg[31:0] mem_addr_o,
    output reg[31:0] mem_wdata_o,
    input wire[31:0] mem_rdata_i

    );


    // 状态
    localparam S_IDLE = 1;
    localparam S_INIT_UART_BAUD = 2;
    localparam S_CLEAR_UART_RX_OVER_FLAG = 3;
    localparam S_WAIT_BYTE = 4;
    localparam S_WAIT_BYTE2 = 5;
    localparam S_GET_BYTE = 6;
    localparam S_REC_FIRST_PACKET = 7;
    localparam S_REC_REMAIN_PACKET = 8;
    localparam S_SEND_ACK = 9;
    localparam S_SEND_NAK = 10;
    localparam S_CRC_START = 11;
    localparam S_CRC_CALC = 12;
    localparam S_CRC_END = 13;
    localparam S_WRITE_MEM = 14;

    reg[3:0] state;

    // 存放串口接收到的数据
    reg[7:0] rx_data[0:131];
    reg[7:0] rec_bytes_index;
    reg[7:0] need_to_rec_bytes;
    reg[15:0] remain_packet_count;
    reg[31:0] fw_file_size;
    reg[31:0] write_mem_addr;
    reg[31:0] write_mem_data;
    reg[7:0] write_mem_byte_index;

    reg[15:0] crc_result;
    reg[3:0] crc_bit_index;
    reg[7:0] crc_byte_index;


    // 向总线请求信号
    assign req_o = (rst == 1'b1 && debug_en_i == 1'b1)? 1'b1: 1'b0;


    always @ (posedge clk) begin
        if (rst == 1'b0 || debug_en_i == 1'b0) begin
            mem_addr_o <= 32'h0;
            mem_we_o <= 1'b0;
            mem_wdata_o <= 32'h0;
            state <= S_IDLE;
            remain_packet_count <= 16'h0;
        end else begin
            case (state)
                S_IDLE: begin
                    mem_addr_o <= `UART_CTRL_REG;
                    mem_wdata_o <= 32'h3;
                    mem_we_o <= 1'b1;
                    state <= S_INIT_UART_BAUD;
                end
                S_INIT_UART_BAUD: begin
                    mem_addr_o <= `UART_BAUD_REG;
                    mem_wdata_o <= `UART_BAUD_115200;
                    mem_we_o <= 1'b1;
                    state <= S_REC_FIRST_PACKET;
                end
                S_REC_FIRST_PACKET: begin
                    remain_packet_count <= 16'h0;
                    mem_addr_o <= 32'h0;
                    mem_we_o <= 1'b0;
                    mem_wdata_o <= 32'h0;
                    state <= S_CLEAR_UART_RX_OVER_FLAG;
                end
                S_REC_REMAIN_PACKET: begin
                    mem_addr_o <= 32'h0;
                    mem_we_o <= 1'b0;
                    mem_wdata_o <= 32'h0;
                    state <= S_CLEAR_UART_RX_OVER_FLAG;
                end
                S_CLEAR_UART_RX_OVER_FLAG: begin
                    mem_addr_o <= `UART_STATUS_REG;
                    mem_wdata_o <= 32'h0;
                    mem_we_o <= 1'b1;
                    state <= S_WAIT_BYTE;
                end
                S_WAIT_BYTE: begin
                    mem_addr_o <= `UART_STATUS_REG;
                    mem_wdata_o <= 32'h0;
                    mem_we_o <= 1'b0;
                    state <= S_WAIT_BYTE2;
                end
                S_WAIT_BYTE2: begin
                    if ((mem_rdata_i & `UART_RX_OVER_FLAG) == `UART_RX_OVER_FLAG) begin
                        mem_addr_o <= `UART_RX_REG;
                        mem_wdata_o <= 32'h0;
                        mem_we_o <= 1'b0;
                        state <= S_GET_BYTE;
                    end
                end
                S_GET_BYTE: begin
                    if (rec_bytes_index == (need_to_rec_bytes - 1'b1)) begin
                        state <= S_CRC_START;
                    end else begin
                        state <= S_CLEAR_UART_RX_OVER_FLAG;
                    end
                end
                S_CRC_START: begin
                    state <= S_CRC_CALC;
                end
                S_CRC_CALC: begin
                    if ((crc_byte_index == need_to_rec_bytes - 2) && crc_bit_index == 4'h8) begin
                        state <= S_CRC_END;
                    end
                end
                S_CRC_END: begin
                    if (crc_result == {rx_data[need_to_rec_bytes - 1], rx_data[need_to_rec_bytes - 2]}) begin
                        if (need_to_rec_bytes == `UART_FIRST_PACKET_LEN && remain_packet_count == 16'h0) begin
                            remain_packet_count <= {7'h0, fw_file_size[31:7]} + 1'b1;
                            state <= S_SEND_ACK;
                        end else begin
                            remain_packet_count <= remain_packet_count - 1'b1;
                            state <= S_WRITE_MEM;
                        end
                    end else begin
                        state <= S_SEND_NAK;
                    end
                end
                S_WRITE_MEM: begin
                    if (write_mem_byte_index == (need_to_rec_bytes + 2)) begin
                        state <= S_SEND_ACK;
                    end else begin
                        mem_addr_o <= write_mem_addr;
                        mem_wdata_o <= write_mem_data;
                        mem_we_o <= 1'b1;
                    end
                end
                S_SEND_ACK: begin
                    mem_addr_o <= `UART_TX_REG;
                    mem_wdata_o <= `UART_RESP_ACK;
                    mem_we_o <= 1'b1;
                    if (remain_packet_count > 0) begin
                        state <= S_REC_REMAIN_PACKET;
                    end else begin
                        state <= S_REC_FIRST_PACKET;
                    end
                end
                S_SEND_NAK: begin
                    mem_addr_o <= `UART_TX_REG;
                    mem_wdata_o <= `UART_RESP_NAK;
                    mem_we_o <= 1'b1;
                    if (remain_packet_count > 0) begin
                        state <= S_REC_REMAIN_PACKET;
                    end else begin
                        state <= S_REC_FIRST_PACKET;
                    end
                end
            endcase
        end
    end

    // 数据包的大小
    always @ (posedge clk) begin
        if (rst == 1'b0 || debug_en_i == 1'b0) begin
            need_to_rec_bytes <= 8'h0;
        end else begin
            case (state)
                S_REC_FIRST_PACKET: begin
                    need_to_rec_bytes <= `UART_FIRST_PACKET_LEN;
                end
                S_REC_REMAIN_PACKET: begin
                    need_to_rec_bytes <= `UART_REMAIN_PACKET_LEN;
                end
            endcase
        end
    end

    // 读接收到的串口数据
    always @ (posedge clk) begin
        if (rst == 1'b0 || debug_en_i == 1'b0) begin
            rec_bytes_index <= 8'h0;
        end else begin
            case (state)
                S_GET_BYTE: begin
                    rx_data[rec_bytes_index] <= mem_rdata_i[7:0];
                    rec_bytes_index <= rec_bytes_index + 1'b1;
                end
                S_REC_FIRST_PACKET: begin
                    rec_bytes_index <= 8'h0;
                end
                S_REC_REMAIN_PACKET: begin
                    rec_bytes_index <= 8'h0;
                end
            endcase
        end
    end

    // 固件大小
    always @ (posedge clk) begin
        if (rst == 1'b0 || debug_en_i == 1'b0) begin
            fw_file_size <= 32'h0;
        end else begin
            case (state)
                S_CRC_START: begin
                    fw_file_size <= {rx_data[61], rx_data[62], rx_data[63], rx_data[64]};
                end
            endcase
        end
    end

    // 烧写固件
    always @ (posedge clk) begin
        if (rst == 1'b0 || debug_en_i == 1'b0) begin
            write_mem_addr <= 32'h0;
            write_mem_data <= 32'h0;
            write_mem_byte_index <= 8'h0;
        end else begin
            case (state)
                S_REC_FIRST_PACKET: begin
                    write_mem_addr <= `ROM_START_ADDR;
                    write_mem_data <= 32'h0;
                    write_mem_byte_index <= 8'h0;
                end
                S_CRC_END: begin
                    write_mem_data <= {rx_data[4], rx_data[3], rx_data[2], rx_data[1]};
                    write_mem_byte_index <= 8'h5;
                    if (write_mem_addr > 0)
                        write_mem_addr <= write_mem_addr - 4;
                end
                S_WRITE_MEM: begin
                    write_mem_addr <= write_mem_addr + 4;
                    write_mem_data <= {rx_data[write_mem_byte_index + 3], rx_data[write_mem_byte_index + 2], rx_data[write_mem_byte_index + 1], rx_data[write_mem_byte_index]};
                    write_mem_byte_index <= write_mem_byte_index + 4;
                end
            endcase
        end
    end

    // CRC计算
    always @ (posedge clk) begin
        if (rst == 1'b0 || debug_en_i == 1'b0) begin
            crc_result <= 16'h0;
            crc_bit_index <= 4'h0;
            crc_byte_index <= 8'h0;
        end else begin
            case (state)
                S_CRC_START: begin
                    crc_result <= 16'hffff;
                    crc_bit_index <= 4'h0;
                    crc_byte_index <= 8'h1;
                end
                S_CRC_CALC: begin
                    if (crc_bit_index == 4'h0) begin
                        crc_result <= crc_result ^ rx_data[crc_byte_index];
                        crc_byte_index <= crc_byte_index + 1'b1;
                        crc_bit_index <= crc_bit_index + 1'b1;
                    end else begin
                        if (crc_bit_index < 4'h9) begin
                            crc_bit_index <= crc_bit_index + 1'b1;
                            if (crc_result[0] == 1'b1) begin
                                crc_result <= {1'b0, crc_result[15:1]} ^ 16'ha001;
                            end else begin
                                crc_result <= {1'b0, crc_result[15:1]};
                            end
                        end else begin
                            crc_bit_index <= 4'h0;
                        end
                    end
                end
            endcase
        end
    end

endmodule