The JOYSTIK editor (BASIC front-end)

This describes the BBC BASIC program in voltmace-delta-14b-driver-joystik.bas — the user-facing half of the Voltmace Delta 14B JOYSTIK software. Line numbers below refer to that program.

What it is for

The Delta 14B handset has a two-axis analogue joystick, two fire buttons, and (via the Delta 14B/1 adaptor) a keypad. Games written for the keyboard can't use it directly. This program lets you map joystick directions, fire buttons and keypad keys onto keyboard keys, then installs a small machine-code resident driver that makes those inputs look like key presses to any game that reads the keyboard with INKEY(-key) (lines 500–510 explain that convention to the user).

You pick a joystick configuration, choose a ready-made mapping for an Acornsoft game (or define your own), optionally test and tune it, and finish. The resident driver then stays at &A00–&AFF while your game is loaded and run.

The companion machine code — the two resident driver variants this program installs — is covered by the disassemblies in driver-a.asm and driver-b.asm.

Shape of the program

Startup and protection (10–170)

Line 10 is a REM whose length byte is stored as 0 and repaired to &17 by the loader before the program runs. Line 50 selects MODE 7, clears Z%, and saves the current BYTEV (OVL%=?&20A:OVH%=?&20B) — the previous OSBYTE vector, which the resident driver will chain to. As in the KEYPAD editor, Z% is a resident integer (at &468) that selects protected behaviour (Z%=0) over an unprotected/developer mode (Z%=1); it is 0 here and nothing changes it, so the protected path always runs. Lines 60–80 accordingly reprogram the BREAK key: a BBC Micro has no f10 key, so soft key 10 (*KEY10) is the "break string" a soft (single) BREAK types into the input. They set it to a self-destruct — empty the program at PAGE, zero &1902–&5000, and print "PROGRAM PROTECTED" — arming the trap rather than firing it now. Line 90 reads the OS version (?&F0C7/?&F0C8); line 130's *FX200,2 additionally clears user memory on the next BREAK (OSBYTE 200 bit 1) while leaving ESCAPE (bit 0) working as the handled "restart" path; and lines 140–150 dimension the working arrays.

Intro and joystick configuration (280–520)

PROCINTRO shows the copyright, then (lines 350–400) asks which configuration is in use:

• Single joystick (S) — line 370 sets H%=7, so PROCASSEM later installs the joystick-only resident driver (variant A), read through the analogue port.
• 1 or 2 joysticks + adaptor box (1/2) — lines 380–390 set H%=35, so the joystick + keypad resident driver (variant B) is installed (which also scans the keypad matrix). Lines 480–481 warn that some programs pulse User-Port P7 and can disturb the keypad.

Lines 420–510 explain that the resident driver simulates up to J% keyboard keys and is compatible with games that read the keyboard via INKEY(-key).

Choosing a mapping (610–990)

PROCGAME lists eight choices (line 610): user-defined plus seven Acornsoft games (named in the T$ table, line 1150). Selecting one (line 640) RESTOREs to the matching DATA line (810–960 for single joystick, 890–960 for the adaptor configurations) and reads a preset list of INKEY key numbers into V%() — the key each joystick input should emulate for that game.

Initialisation tables (1080–1190)

PROCINIT sets the sensitivity (SEN%, and the thresholds SL%/SH%, line 1080), then reads:

• K$() (line 1100) — printable key names (f0…f9, A…Z, digits, symbols, ESCAPE, cursor keys, …).
• N%() (line 1120) — the INKEY (negative-INKEY) value for each of those keys.
• T$() (line 1150) — the game names.
• C$() (line 1170) and CH%() (line 1180) — the on-screen labels and ADC channel for each joystick input (direction, fire, keypad cell).

Defining and displaying keys (1000–1240)

For user-defined mappings, PROCEDIT (line 1020) restores the saved BYTEV so the keyboard reads normally, then PROCKEY (line 1200) waits for you to hold a key, identifies it by scanning INKEY(-N%(n)) for every key, and records its INKEY value in V%(). PROCDEFAULTPRINT (line 1040) shows the current mapping.

Building the resident driver (1720–1870)

PROCASSEM turns the mapping into a working resident driver:

• Line 1730 recovers the previous BYTEV (R%) to chain to.
• Line 1740 points TBL% at &AB0 — the resident driver's joystick_map.
• Line 1750 chooses the resident driver source: &1A00 (variant A) when H%=7, else &1B00 (variant B).
• Line 1760 copies that 256-byte resident driver down to &A00.
• Lines 1780–1830 poke the mapping into joystick_map: each 2-byte entry gets the negated INKEY value (-V%(...)) the resident driver should respond to.
• Line 1840 patches the chain slot: ?&AFA=&4C (a JMP opcode) with &AFB/&AFC set to R%, so non-INKEY OSBYTEs pass to the original vector.
• Line 1850 writes the sensitivity thresholds into &AFD/&AFE.
• Line 1860 CALL &A00 runs the install routine, hooking BYTEV.

Test, tune and finish (1380–2010)

PROCTERM (line 1380) offers Edit / Test / Alter sensitivity / Finish. PROCTEST (line 1470) shows a live grid: PROCDISAD/PROCDISLOW/PROCDISHIGH threshold the analogue axes (ADVAL), PROCDISFIRE reads the fire buttons (ADVAL(0)), and PROCDISUP reads the keypad matrix through the User VIA. PROCJOY (line 1880) re-computes SL%/SH% from a 1–9 sensitivity and re-pokes &AFD/&AFE live. PROCFINI (line 1250) tells you how to *SAVE the resident driver (*SAVE <name> A00 +100) and re-install it later (*KEY10 CALL &A00). The finish code (lines 1960–2010) blanks and detaches the program, leaving only the configured resident driver.