function timer_cb(Ihandle /*ih*/)
    IupUpdate(canvas)
    return IUP_IGNORE
end function

Ihandle timer = IupTimer(Icallback("timer_cb"), 1000)

function key_cb(Ihandle /*ih*/, atom c)
    if c=K_ESC then return IUP_CLOSE end if
    if c=K_F5 then
        iteration = 0
        IupSetInt(timer,"RUN",1)                -- (restart timer)
    end if
    return IUP_CONTINUE
end function

IupSetCallback(dlg, "K_ANY", Icallback("key_cb"))