ON TIMER(n)

The ON TIMER statement sets up a timed event to be repeated at specified intervals throughout a program when enabled.

Syntax

ON TIMER(seconds%) GOSUB {lineLabel|lineNumber}

ON TIMER([number%,] seconds!) { SUBprocedure | GOSUB {lineLabel|lineNumber} }

In the first syntax, the INTEGER seconds% parameter can be from 1 to 86400 seconds (one day).
A TIMER ON statement must follow an ON TIMER event setup to initiate it.
TIMER STOP disables timer events but remembers previous events when enabled again by a TIMER ON statement, and the recorded events may be executed immediately if a timer event has occurred.
TIMER OFF disables timer event trapping. Events will not be remembered in a subsequent TIMER ON statement.
ON TIMER events will interrupt a SLEEP call and RETURN to running program procedures.
Only one TIMER event can be set at a time using this legacy syntax and all TIMER code must be in the main code, as it uses GOSUB.

QB64 can use multiple numbered timer events and SINGLE floating point second values down to one millisecond (.001).
The TIMER number% must be obtained from the _FREETIMER function. Store _FREETIMER numbers in a variable or an array to be able to reference them later.
If the TIMER number is omitted or ON TIMER(0, seconds!) is used, then the TIMER used is the base TIMER (same as in the legacy syntax above).
SUB procedures are allowed to be referenced, but CALL must not be used.
SUB parameter values are passed by value and should be SHARED or literal values.
Specific TIMER events can be turned on, suspended, turned off or freed using TIMER(n) ON, STOP, OFF or FREE.
Use TIMER(n) FREE to release a timer event after it has been turned off or is no longer used.
- The base TIMER cannot be freed.
QB64 allows TIMER statements to also be inside of SUB and FUNCTION procedures.
ON TIMER events will interrupt a SLEEP call and RETURN to running program procedures.
$CHECKING:OFF can disable all QB64 event checking. Setting $CHECKING:OFF is only designed for 100% stable, error-less sections of code, where every CPU cycle saved counts.

The TIMER function can be used to find timed intervals down to 1 millisecond(.001) accuracy.
The _DELAY statement can be used to delay program execution for intervals down to milliseconds.
_LIMIT can slow down loops to a specified number of frames per second. This can also alleviate a program's CPU usage.

Example: Using a numbered TIMER to check the mouse button press status in QB64.

DIM SHARED Button AS LONG 'share variable value with Sub t1 = _FREE TIMER 'get a timer number from _FREETIMER ONLY! ON TIMER(t1, .05) MouseClick TIMER(t1) ON DO LOCATE 1, 1 IF Button THEN PRINT "Mouse button"; Button; "is pressed."; ELSE PRINT SPACE$(70) END IF _DISPLAY LOOP UNTIL INKEY$ = CHR$(27) TIMER(t1) OFF TIMER(t1) FREE 'release timer END SUB MouseClick DO WHILE _MOUSEINPUT IF _MOUSEBUTTON(1) THEN COLOR 10: Button = 1 ELSEIF _MOUSEBUTTON(2) THEN COLOR 12: Button = 2 ELSE Button = 0 END IF LOOP END SUB