ELEC70056-HSV-CW2/rtl/AHB_GPIO/AHBGPIO.sv

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module AHBGPIO
( input  wire        HCLK
, input  wire        HRESETn
, input  wire [31:0] HADDR
, input  wire [ 1:0] HTRANS
, input  wire [31:0] HWDATA
, input  wire        HWRITE
, input  wire        HSEL
, input  wire        HREADY
, input  wire [16:0] GPIOIN
, input  wire        PARITYSEL
, input  wire        INJECT_FAULT
	//Output
, output wire        HREADYOUT
, output wire [31:0] HRDATA
, output wire [16:0] GPIOOUT
, output wire        PARITYERR
);

  localparam [7:0] gpio_data_addr = 8'h00;
  localparam [7:0] gpio_dir_addr = 8'h04;

  reg [15:0] gpio_dataout;
  reg        gpio_parityout;
  reg [15:0] gpio_datain;
  reg        gpio_parityerr;
  reg [15:0] gpio_dir;
  reg [15:0] gpio_data_next;
  reg [31:0] last_HADDR;
  reg [ 1:0] last_HTRANS;
  reg        last_HWRITE;
  reg        last_HSEL;

  integer i;

  assign HREADYOUT = 1'b1;

// Set Registers from address phase
  always_ff @(posedge HCLK)
    if(HREADY) begin
      last_HADDR <= HADDR;
      last_HTRANS <= HTRANS;
      last_HWRITE <= HWRITE;
      last_HSEL <= HSEL;
    end

  // Update in/out switch
  always_ff @(posedge HCLK, negedge HRESETn)
    if(!HRESETn)
      gpio_dir <= 16'h0000;
    else if ((last_HADDR[7:0] == gpio_dir_addr) & last_HSEL & last_HWRITE & last_HTRANS[1])
      gpio_dir <= HWDATA[15:0];

  // Update output value
  always_ff @(posedge HCLK, negedge HRESETn)
    if(!HRESETn)
      {gpio_parityout, gpio_dataout} <= 17'd0;
    else if ((gpio_dir == 16'h0001) & (last_HADDR[7:0] == gpio_data_addr) & last_HSEL & last_HWRITE & last_HTRANS[1]) begin
      gpio_dataout <= HWDATA[15:0];
      gpio_parityout <= ~^{HWDATA[15:0],PARITYSEL,INJECT_FAULT};
    end

  // Update input value
  always_ff @(posedge HCLK, negedge HRESETn)
    if(!HRESETn)
      gpio_datain <= 16'h0000;
    else if (gpio_dir == 16'h0000) begin
      gpio_datain <= GPIOIN[15:0];
      gpio_parityerr <= ~^{GPIOIN,PARITYSEL,INJECT_FAULT};
    end
    else if (gpio_dir == 16'h0001)
      gpio_datain <= GPIOOUT;

  assign HRDATA[15:0] = gpio_datain;
  assign GPIOOUT = {gpio_parityout, gpio_dataout};
  assign PARITYERR = gpio_parityerr;

  //check behaviour
    
  assert_parity: assert property
    ( @posedge(HCLK) disable iff (!HRESETn)
      !PARITYERR;
    );

  assert_gpio_write: assert property
    ( @posedge(HCLK) disable iff (!HRESETn)
      ((gpio_dir == 16'h0001)
        && (HADDR[7:0] == gpio_data_addr)
        && HSEL
        && HWRITE
        && HTRANS[1])
      |-> (GPIOOUT[15:0] == $past(HWDATA[15:0], 1))
    );

  assert_gpio_read: assert property
    ( @posedge(HCLK) disable iff (!HRESETn)
      ((gpio_dir == 16'h0000)
        && (HADDR[7:0] == gpio_data_addr)
        // && HSEL // HSEL not used in Read always_ff
        && !HWRITE
        && HTRANS[1])
      |-> (HRDATA[15:0] == $past(GPIOIN[15:0], 1)
           && HREADYOUT)
    );

  assert_gpio_dir: assert property
    ( @posedge(HCLK) disable iff (!HRESETn)
      ((HADDR[7:0] == gpio_dir_addr)
        && HSEL
        && HWRITE
        && HTRANS[1])
      |-> (gpio_dir == $past(HWDATA[15:0], 1))
    );

endmodule