module
IntervalTimer

// Measures fixed time interval to activate solenoid and LEDs.

(
// Clock and reset:
iG$MasterClock,		// Master clock
iG$MasterReset,		// Master reset (active high)

// Control point signals from controller:
iC$InitializeTimer,	// Set timer to beginning of interval
iC$EnableTimer,			// Allow timer to operate

// Condition signals to controller:
oS$IntervalIsComplete,	// Indicates end of time interval

// Data outputs:
oD$IntervalTimer	// Value of interval timer


);

parameter p$TimeInterval = 20;	// Number of clock periods (assumes
											// 10-Hz master clock.

input	iG$MasterClock;
input	iG$MasterReset;
input iC$InitializeTimer;
input iC$EnableTimer;

output oS$IntervalIsComplete;
output [4:0] oD$IntervalTimer;

reg [4:0] oD$IntervalTimer;


always @ (posedge iG$MasterClock or posedge iG$MasterReset)
	if (iG$MasterReset) 
		oD$IntervalTimer <= p$TimeInterval-1;
	else
		if (iC$InitializeTimer)
			oD$IntervalTimer <= p$TimeInterval-1;
		else if (iC$EnableTimer) 
			oD$IntervalTimer <= oD$IntervalTimer - 1;
		
assign oS$IntervalIsComplete = (oD$IntervalTimer == 0);

endmodule