FPGAWorkshop16Notes

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//////////////////////////////////////////////////////////////////////////////////
// Company: 
// Engineer: 
// 
// Create Date:    11:23:27 01/28/2010 
// Design Name: 
// Module Name:    frequency_counter 
// Project Name: 
// Target Devices: 
// Tool versions:  
// Description: Verilog implementatino of the frequency counter reference
// design from Xilinx for Spartan 3E Starter Kit
//
// Dependencies: 
//
// Revision: 
// Revision 0.01 - File Created
// Additional Comments: 
//
//////////////////////////////////////////////////////////////////////////////////
module frequency_counter(
    output [7:0] led,
    input [4:0] sw,
    output strataflash_oe,
    output strataflash_ce,
    output strataflash_we,
    inout [7:4] lcd_d,
    output lcd_rs,
    output lcd_rw,
    output lcd_e,
    input sma_clk,
    input clk_50mhz
    );

	// signals for counting the test clock
	reg [3:0] ab_switch_delay;
	reg a_count_ce, b_count_ce;
	reg [31:0] a_count, b_count;
	reg a_count_rst, b_count_rst;
	reg freq_for_measurement;
	wire test_clk;
	
	// signals for 1 second interrupt generation and couter switching
	reg ab_switch;	
	reg [99:0] interrupt_delay;
	reg [25:0] one_second_count;
	reg one_second_pulse;
	reg interrupt;
	reg [7:0] source_control;

	// signals for processor interconnect
	reg [7:0] in_port;
	wire [7:0] out_port;
	wire write_strobe, read_strobe;
	wire [7:0] port_id;
	wire interrupt_ack;
	wire [17:0] instruction;
	wire [9:0] address;

	// lcd wires
	reg [7:0] lcd_reg;
	wire lcd_drive;
	wire lcd_output_data;

	// led reg
	reg [7:0] led_reg;

	// ring osscillator instantiations
	ring_osc logic_oscillator (.reset(source_control[6]),.osc_out(ring_oscillator));
	ring_osc2 logic_oscillator2 (.reset(source_control[6]),.osc_out(ring_oscillator2));

	// frequency selection mux - purely combinational
	always@(sma_clk or clk_50mhz or ring_oscillator or ring_oscillator2)
		if(source_control[1:0] == 2'b00)
			freq_for_measurement = sma_clk;
		else if(source_control[1:0] == 2'b01)
			freq_for_measurement = clk_50mhz;
		else if(source_control[1:0] == 2'b10)
			freq_for_measurement = ring_oscillator2;
		else
			freq_for_measurement = ring_oscillator;

	// global clock buffer the test clock		
	BUFG buffer_clkin(.O(test_clk), .I(freq_for_measurement));		

	// counter switch control
	always@(posedge test_clk)		
	begin
		ab_switch_delay <= {ab_switch_delay[2:0], ab_switch};
		case(ab_switch_delay[3:1])
			3'b000: begin
				a_count_ce <= 1;
				b_count_ce <= 0;
				end
			3'b111: begin
				a_count_ce <= 0;
				b_count_ce <= 1;
			end
			default: begin
				a_count_ce <= 1;
				b_count_ce <= 0;
			end
		endcase
	end
	
	// test counters
	always@(posedge test_clk or posedge a_count_rst)
		if(a_count_rst)
			a_count <= 'b0;
		else if(a_count_ce)
			a_count <= a_count+1;
		else
			a_count <= a_count;

	always@(posedge test_clk or posedge b_count_rst)
		if(b_count_rst)
			b_count <= 'b0;
		else if(b_count_ce)
			b_count <= b_count+1;
		else
			b_count <= b_count;	

	// one second interrupt generation and clock switching
/*	always@(posedge clk_50mhz)
	begin
		// divide by 50,000,000 to generate pulse
		if(one_second_count == 26'd49999999)
		begin
			one_second_count <= 'b0;
			one_second_pulse <= 1'b1;
		end
		else
		begin
			one_second_count <= one_second_count + 1;
			one_second_pulse <= 1'b0;
		end
		
		// delay 100 clock cycles before generating interrupt
		interrupt_delay <= {interrupt_delay[98:0], one_second_pulse};
		
		// interrupt generation
		if (interrupt_ack == 1'b1)
			interrupt <= 1'b0;
		else if (interrupt_delay[99] == 1'b1)
			interrupt <= 1'b1;
		else
			interrupt <= interrupt;
			
		// counter selection switch toggle's each second
		if (one_second_pulse == 1'b1)
			ab_switch <= ~ab_switch;
	end*/
always@(posedge clk_50mhz)
	begin
		// divide by 50,000,000 to generate pulse
		if(one_second_count == 26'd49999999)
		begin
			one_second_count <= 'b0;
			one_second_pulse <= 1'b1;
		end
		else
		begin
			one_second_count <= one_second_count + 1;
			one_second_pulse <= 1'b0;
		end
	end
always@(posedge clk_50mhz)

begin
			// delay 100 clock cycles before generating interrupt
		interrupt_delay <= {interrupt_delay[98:0], one_second_pulse};
end

always@(posedge clk_50mhz)
	begin
			// interrupt generation
		if (interrupt_ack == 1'b1)
			interrupt <= 1'b0;
		else if (interrupt_delay[99] == 1'b1)
			interrupt <= 1'b1;
		else
			interrupt <= interrupt;
end		

always@(posedge clk_50mhz)
begin
	// counter selection switch toggle's each second
		if (one_second_pulse == 1'b1)
			ab_switch <= ~ab_switch;
		else
			ab_switch <= ab_switch;
		end
		
		
	// picoblaze instantiation
	kcpsm3 processor (.address(address), 
		.instruction(instruction),
		.port_id(port_id),
		.write_strobe(write_strobe),
		.out_port(out_port),
		.read_strobe(read_strobe),
		.in_port(in_port),
		.interrupt(interrupt),
		.interrupt_ack(interrupt_ack),
		.reset(reset),
		.clk(clk_50mhz));
	fc_ctrl program_rom (.address(address),
		.instruction(instruction),
		.proc_reset(proc_reset),
		.clk(clk_50mhz));
		
	// processor input ports
	always@ (posedge clk_50mhz)
		case(port_id[7:4])
			// read A counter
			4'b0000: in_port <= a_count[7:0];
			4'b0001: in_port <= a_count[15:8];
			4'b0010: in_port <= a_count[23:16];
			4'b0011: in_port <= a_count[31:24];			
			// read B counter
			4'b0100: in_port <= b_count[7:0];
			4'b0101: in_port <= b_count[15:8];
			4'b0110: in_port <= b_count[23:16];
			4'b0111: in_port <= b_count[31:24];		
			// read slide switches
			4'b1000: in_port <= {3'b000, ab_switch, sw};
			// read LC Ddata at address 90 hex
			4'b1001: in_port <= {lcd_d, 4'b0000};
			// original design used a dont care condition
			// I've decided to let it retain its value.
			default: in_port <= in_port;
		endcase	
	
	// output ports
	always@ (posedge clk_50mhz)
		if(write_strobe)
			case(port_id[3:0])
				// LED register at address 0x01
				4'b0001: led_reg <= out_port;
				// Counter reset controls at 0x02
				4'b0010: begin
					a_count_rst <= out_port[0];
					b_count_rst <= out_port[1];
					end
				// LCD data/controls at 0x04
				4'b0100: begin
					lcd_reg			<= out_port;
					end
				// Source selection and control at 0x08
				4'b1000: source_control <= out_port;
			endcase

	// LCD controls
	assign lcd_rw_control = lcd_reg[1];
	assign lcd_drive = lcd_reg[3];
	assign lcd_output_data = lcd_reg [7:4];
	// LCD Outputs
	assign lcd_e = lcd_reg[0];
	assign lcd_rw = lcd_rw_control && lcd_drive;
	assign lcd_rs = lcd_reg[2];
	assign lcd_d = ((lcd_rw_control == 1'b0) && (lcd_drive == 1'b1)) ? lcd_output_data : 4'bZZZZ;
	
	// LED assignment
	//assign led = led_reg;
	// Debug assignments
	assign led[7]=led_reg[7]; //A counter
	assign led[6]=led_reg[0]; //B counter
	assign led[5]=a_count[10]; // should toggle at 8hz when enabled
	assign led[4]=b_count[10]; // should toggle at 8hz when enabled
	assign led[3]=one_second_count[24]; // should toggle very fast.
	assign led[2]=one_second_pulse; // once per second
	assign led[1]=interrupt_ack; //interrupt ack
	assign led[0]=interrupt; //interrupt

	// strataflash chip enable signals to disable onboard strataflash
	assign strataflash_we = 1'b1;
	assign strataflash_ce = 1'b1;
	assign strataflash_oe = 1'b1;

endmodule