virtual register of FAP video card

cpu_vreg.v

module cpu_vreg(
	input wire clk,
	input wire copy_in_progress,
	input wire cpu_rd,
	input wire cpu_wr,
	input wire cpu_mreq,
	input wire [15:0] cpu_addr,
	inout wire [7:0] cpu_data,
	output reg back_vram_wr_low,
	output reg [12:0] back_vram_addr,
	output reg [7:0] back_vram_data
	);

always @(posedge clk)
begin
	if(copy_in_progress == 0 && cpu_wr == 0 && cpu_mreq == 0 && cpu_addr >= 16'h8000) begin
		back_vram_addr = cpu_addr[12:0];
		back_vram_data = cpu_data;
		back_vram_wr_low = 0;
	end	
	else begin
		back_vram_wr_low = 1;
		back_vram_addr = 13'bzzzzzzzzzzzzz;
		back_vram_data = 8'bzzzzzzzz;
	end
end

endmodule