Count Active Play Ticks in BBC Micro BASIC

A pause menu should not quietly use up the player’s time allowance. This clock counts serviced active-play ticks, so menu activity and play time can follow different rules.

Include and initialise

Reserve public L/H/P/R/O, private T and lines 3000–3200. There are no arrays. Combine routines.bas and your caller with build.py and keep END, STOP or a jump before the helper. C64/BBC use GOSUB; Spectrum uses GO SUB.

Call 3000 at a new-session boundary. It clears all public fields. L/H retain a low-byte-first unsigned counter, representing L + 256*H. Set a different starting counter afterwards if the game needs one.

Supply pause and reset state

Set P to the current pause flag and R to a reset request, then call 3100. Any nonzero byte means true. Reset takes priority: it clears L/H even while paused. Without reset, a paused call leaves the counter alone; a running call adds one modulo 65,536. P/R survive.

Reusable numbered routines

3000 LET L=0: LET H=0: LET P=0: LET R=0: LET O=0: RETURN
3100 LET O=0
3110 IF L<0 OR L>255 OR L<>INT (L) THEN RETURN
3120 IF H<0 OR H>255 OR H<>INT (H) THEN RETURN
3130 IF P<0 OR P>255 OR P<>INT (P) THEN RETURN
3140 IF R<0 OR R>255 OR R<>INT (R) THEN RETURN
3150 LET O=1
3160 IF R<>0 THEN LET L=0: LET H=0: RETURN
3170 IF P<>0 THEN RETURN
3180 LET T=L+256*H+1
3190 IF T>65535 THEN LET T=0
3200 LET H=INT (T/256): LET L=T-256*H: RETURN

All four inputs/state must be integral bytes. Invalid input clears O and leaves L/H/P/R untouched. Validation occurs before reset; a reset request does not silently repair damaged non-byte fields. Use the known initialisation entry at a deliberate recovery boundary.

Separate menu time from play time

The normal client starts at 254, services run/pause/pause/run and checks 256. The custom start at 255 checks 257, crossing the carry one call earlier. Both then reset while paused, remain paused and run once, finishing at one. The native table separately checks the 65,535-to-zero wrap.

Example calls from the maintained caller

70 GOSUB 3000: LET AA=0: LET BB=0
80 LET L=254: LET H=0
90 LET P=0: LET R=0: GOSUB 3100: GOSUB 2000
100 LET P=1: LET R=0: GOSUB 3100: GOSUB 2000
110 LET P=1: LET R=0: GOSUB 3100: GOSUB 2000
120 LET P=0: LET R=0: GOSUB 3100: GOSUB 2000
130 IF L+256*H=256 THEN LET AA=1
140 LET P=1: LET R=1: GOSUB 3100: GOSUB 2000
150 LET P=1: LET R=0: GOSUB 3100: GOSUB 2000
160 LET P=0: LET R=0: GOSUB 3100: GOSUB 2000
170 IF L=1 AND H=0 THEN LET BB=1
180 PRINT "TIME RESULTS";AA;BB
190 ?(MB+995)=AA: ?(MB+996)=BB: ?(MB+997)=GD: ?(MB+998)=WC-256*INT (WC/256): ?(MB+999)=INT (WC/256): ?(MB+1000)=239: STOP

Line 2000, AA/BB/JJ (Z on Spectrum) and mailbox writes are diagnostics. A game supplies one service per intended tick and can keep another always-running clock for menu animation. No hardware clock or interrupt is installed by this helper. If the caller withholds service during pause instead, remember that a reset still needs its own path.

Customise duration and wrap

These are ticks, not seconds. Conversion depends on the actual service rate. The 16-bit counter eventually wraps; a subtraction-based deadline must use its own documented safe interval rather than treating a wrapped value as a lifetime total. Wider counters postpone wrap at a storage and arithmetic cost.

An ordinary BASIC scalar may be a simpler active counter when binary interchange is unnecessary. The two-byte version makes the assembly/shared-data representation explicit. Decide whether slow-motion, an options menu or an end-of-level tally counts as active play, then supply P consistently. The routine cannot choose that rule for the game.

Mistake and repair

The wrong caller forces P to zero before every call. Time continues through the two pause samples, and after reset it also counts the paused sample. Both saved checks fail. Supply the actual pause state or deliberately stop servicing active time. Repaired source and loaded program match normal exactly.

Cost and Maths for Games

Each valid call has a bounded reset, hold or increment path. The increment widens before splitting the result, so the carry and full wrap are deliberate. It allocates nothing and makes no display or device calls.

Maths for Games connects modular counters, place value and elapsed intervals. The Craft connects pause behaviour and timed decisions to fair, predictable play.

Global names and line numbers

BASIC numeric names, arrays and numbered lines are global. To combine helpers, rename public and private fields and renumber the helper together with every GO SUB/GO TO reference. Keep each state block under one owner. The maintained build.py rejects duplicate line numbers; it does not automatically namespace or renumber routines.

Machine and measured size

This helper uses scalar numeric fields and allocates no arrays. Its diagnostic uses MODE 7 and HIMEM=&6000 to separate program storage, mailbox and screen. The helper itself changes neither mode nor HIMEM.

The numbered helper occupies 311 tokenised program bytes on this interpreter, including line headers. This excludes the caller, test tables, numeric scalar/array storage, interpreter stacks and ROM. Tokenised size is not machine-code size or a hardware-cycle count. No real-time or whole-game performance budget is inferred from the diagnostic. The caller’s AA/BB, JJ and RAM mailbox are observation machinery, not required game state.

Execution evidence

Working, custom, deliberately wrong and exact repaired callers executed through BBC Micro’s stock BASIC interpreter under Emu198x 0.44.2. Build198x 0.2.9 tokenises C64 PRG and Spectrum TAP programs. C64 enters stock RUN, Spectrum uses ROM tape loading, and BBC enters every numbered source line through MOS/BASIC. Actual loaded program bytes, complete state packets, positive completion/count/guards and visible result pixels are checked. After the positive completion marker, the observer advances two complete display frames before capturing, so a partially scanned final character cannot masquerade as a finished picture. Firmware is not distributed.

An independent mathematical/order model checks the trace and rejects altered source, configuration, loaded program, state, completion and image evidence. Host exhaustive checks complement the native boundary/sequential examples; those host ranges are not claimed as natively exhaustive. The supplied diagnostic callers deliberately end with STOP; the interpreter report is expected. The wrong caller prints 0,0 and the normal/custom/repaired callers print 1,1.

Public CI checks retained evidence; it does not execute restricted firmware. Refresh with python3 scripts/verify-basic-temporal.py pause-clock bbc-micro --tools /path/to/extracted/releases and inspect with python3 scripts/check-basic-temporal.py pause-clock.

Explore further

Compare the assembly technique. The BASIC game-flow routine makes session boundaries explicit. Complete source and native evidence.