APB Slave Design

module apb_slave
#(
  REG1_ADDR = 8'h00,
  REG2_ADDR = 8'h04,
  REG3_ADDR = 8'h08
)
(
  // input signals
  input pclk,
  input presetn,
  input psel,
  input penable,
  input pwrite,
  input [31:0] pwdata,
  input [31:0] paddr,
  output reg [31:0] prdata,
  
);

// 读写信号
wire apb_write;
wire apb_read;

// 定义三个寄存器
reg [31:0] reg1;
reg [31:0] reg2;
reg [31:0] reg3;

reg [31:0] dummy_reg; 

// 产生读写信号
assign apb_write = pwrite && psel && penable;
assign apb_read = (!pwrite) && psel && penable;

// 写操作
always @ (posedge pclk or negedge presetn) begin
  if(!presetn)
    begin
      reg1 <= 32'b0;
      reg2 <= 32'b0;
      reg3 <= 32'b0;
    end
  else if(ahb_write)
    begin
      case (paddr[7:0])
        REG1_ADDR:reg1 <= pwdata;
        REG2_ADDR:reg2 <= pwdata;
        REG3_ADDR:reg3 <= pwdata;
        default:dummy_reg <= pwdata;
      endcase
    end
end

always @ (posedge pclk or negedge presetn) begin
 if(ahb_read)
    begin
      case (paddr[7:0])
        REG1_ADDR:prdata <= reg1;
        REG2_ADDR:prdata <= reg2;
        REG3_ADDR:prdata <= reg3;
        default:prdata <= dummy_reg;
      endcase
    end
end

endmodule