///////////////////////////////////////////////////////////////////////////////////////
//
// PROM MODULE - 1k Words program memory.
//
///////////////////////////////////////////////////////////////////////////////////////

// Timescale Directive
`timescale 100ps / 10ps

// 1024 words of ROM
`define rom_top 1023

module prom( Data_bus, Address_bus );

//
// I/O Declarations
//
input [31:0] Address_bus;
output [31:0] Data_bus;

//
// Extra declarations for "Backdoor" programming
//
reg PROMwrite;
reg PROMclear;
reg [31:0] PROMaddress;
reg [31:0] PROMdata_in;

//
// Register Declaration
//
reg [31:0] Data_stored [ `rom_top:0 ];
reg [31:0] a;
reg [31:0] Countfrom;

//
// Continuous Assignment
//
assign Data_bus = (Address_bus[1:0] == 0) ? Data_stored [Address_bus[31:2]] : 32'bx;


//
// For "backdoor" programming
//
initial
begin
	PROMwrite = 0;
	PROMclear = 0;
	PROMdata_in = 0;
	PROMaddress = 0;
end

always @(posedge PROMwrite)
begin
	$display("Update PROM[%d] = %d",PROMaddress[31:2],PROMdata_in);
	Data_stored [PROMaddress[31:2]] = PROMdata_in;
	PROMwrite = 0;
end

always @(posedge PROMclear)
begin
	$display("Clear PROM");
	for (a = 0; a <= `rom_top; a = a + 1)
		Data_stored[a]='h80000000;
	PROMclear = 0;
end


////////////////////////////////////////////////////////////////////////////
// PROGRAM INSTRUCTIONS
////////////////////////////////////////////////////////////////////////////
initial

begin

// Set repeat variable
Countfrom = 20;

//	Initialise all to NOP
for (a = 0; a <= `rom_top; a = a + 1)
	Data_stored[a]={32'b10000000000000000000000000000000 };

//	ADD R0,1, R1
Data_stored[0]={2'b10, 5'b00001, 6'b000000, 5'b00000, 1'b1, 13'b0000000000001 };

//	ADD R0,2, R2
Data_stored[1]={2'b10, 5'b00010, 6'b000000, 5'b00000, 1'b1, 13'b0000000000010 };

//	ADD R0,3, R3
Data_stored[2]={2'b10, 5'b00011, 6'b000000, 5'b00000, 1'b1, 13'b0000000000011 };

//	ADD R0,4, R4
Data_stored[3]={2'b10, 5'b00100, 6'b000000, 5'b00000, 1'b1, 13'b0000000000100 };

//	XOR R2,7, R5
Data_stored[4]={2'b10, 5'b00101, 6'b000011, 5'b00010, 1'b1, 13'b0000000000111 };

//	SLL R3,R1, R6
Data_stored[5]={2'b10, 5'b00110, 6'b100101, 5'b00011, 1'b0, 8'b00000000, 5'b00001 };


end


endmodule