-- @param pulse length in ticks
local pulseLength = 5

-- @param clock speed in ticks
local clockSpeed = 20

-- @param pulse direction
local pulseSide = "down"
local inputSide = "front"

-- @param redstone signal to disable clock
-- true = redstone turns on
-- false = redstone turns off
-- nil = ignore redstone
local redstone = nil

while true do
	-- use redstone signal to determine if the clock is on or off
    while redstone == nil or redstone == rs.getInput(inputSide) do
        rs.setOutput(pulseSide, true)
        sleep(pulseLength / 20)

        rs.setOutput(pulseSide, false)
        sleep((clockSpeed - pulseLength) / 20)
    end

	-- if we dropped out of the clock loop, wait for redstone
    event = os.pullEvent("redstone")
end