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////////////////////////////////////////////////////////////////////////////////////////////////
////                                                              							////
////                                                              							////
////  	This file is part of the project                 									////
////	"instruction_list_pipelined_processor_with_peripherals"								////
////                                                              							////
////  http://opencores.org/project,instruction_list_pipelined_processor_with_peripherals	////
////                                                              							////
////                                                              							////
//// 				 Author:                                                  				////
////      			- Mahesh Sukhdeo Palve													////
////																						////
////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////
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//// 					This source file may be used and distributed without         		////
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//// 					the original copyright notice and the associated disclaimer. 		////
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//// 					This source file is free software; you can redistribute it   		////
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////////////////////////////////////////////////////////////////////////////////////////////////
 
`include "timescale.v"
`include "defines.v"
 
 
module timer (clk, en, reset, type, preset, DN, TT, ACC);
 
	input clk, en, reset;
	input [`tcTypeLen-1:0] type;
	input [`tcPresetLen-1:0] preset;
 
	output DN, TT;
	output [`tcAccLen-1:0] ACC;
 
	reg DN = 0, TT = 0;
	reg [`tcAccLen-1:0] ACC = 0;
 
	reg [`tcTypeLen-1:0]	TimerType;
	reg [`tcTypeLen-1:0]	typeNext;
 
 
 
	parameter	OnDelayTimer			= `tcTypeLen'b0;
	parameter	OffDelayTimer			= `tcTypeLen'b1;
	parameter	RetOnDelayTimer		= `tcTypeLen'b10;
	parameter	defaultType				= `tcTypeLen'b11;
 
	always @ (type)
	begin
		case (type)
 
		`timerType1		:	begin
								typeNext = OnDelayTimer;
								end
 
		`timerType2		:	begin
								typeNext = OffDelayTimer;
								end
 
		`timerType3		:	begin
								typeNext = RetOnDelayTimer;
								end
 
		default			:	begin
 
								$display("\nTimer is defined for unknown type.\n Valid types: On-delay, Off-delay, retentive-on-delay");
								end
 
		endcase
	end
 
 
	always @ (posedge clk or posedge reset)
	begin
		if (reset)
		begin
			$write ("\ntimer module is reset	");
			TimerType = defaultType;
		end
		else
		begin
			TimerType = typeNext;
		end
	end
 
 
	always @ (posedge clk)
	begin
 
 
		case (TimerType)
 
		OnDelayTimer	:	begin
										if (reset)
										begin
											ACC = `tcAccLen'b0;
											DN = 1'b0;
											TT = 1'b0;
										end
										else
										begin
											if (en)
											begin
												if (ACC < preset)
												begin
													ACC = ACC + 1'b1;
													DN = 1'b0;
													TT = 1'b1;
												end
												else if (ACC >= preset)
												begin
													ACC = ACC;
 
													DN = 1'b1;
													TT = 1'b0;
												end
											end
											else
											begin
												ACC = `tcAccLen'b0;	// if not enabled
												DN = 1'b0;
												TT = 1'b0;
											end
										end
									end	// end this case
 
		OffDelayTimer	:	begin							// not correct implementation!
										if (reset)
										begin
											ACC = `tcAccLen'b0;
											DN = 1'b0;
											TT = 1'b0;
										end
										else
										begin
											if (!en)
											begin
												if (ACC < preset)
												begin
													ACC = ACC + 1'b1;
													DN = 1'b0;
													TT = 1'b1;
												end
												else if (ACC >= preset)
												begin
													ACC = ACC;
													DN = 1'b1;
													TT = 1'b0;
												end
											end
											else
											begin
												ACC = `tcAccLen'b0;	// if not enabled
												DN = 1'b0;
												TT = 1'b0;
											end
										end
									end	// end this case
 
		RetOnDelayTimer	:	begin
 
										if (reset)
										begin
											ACC = `tcAccLen'b0;
											DN = 1'b0;
											TT = 1'b0;
										end
										else
										begin
											if (en)
											begin
												if (ACC < preset)
												begin
													ACC = ACC + 1'b1;
													DN = 1'b0;
													TT = 1'b1;
												end
												else if (ACC >= preset)
												begin
													ACC = ACC;
													DN = 1'b1;
 
 
 
 
													TT = 1'b0;
												end
											end
											else
											begin
												ACC = ACC;	// retain ACC
												DN = 1'b0;
												TT = 1'b0;
											end
										end
									end	// end this case
 
 
				default		:	begin
									if (!reset)
									$display("\nError in timer type	");
									end
 
				endcase
 
	end
 
 
endmodule