Console Physics skill

console-physics

The Physics Tuner finds the constants behind how a game feels and changes them. PS2 games do their physics in single-precision floats (the EE's FPU has no doubles), so a top speed, a gravity or a jump impulse is a 32-bit float somewhere: in the ELF's data, or built straight into the code by two instructions. The tool finds the candidates; PCSX2 tells you which one is the real one; /console-mod builds the winner into the port.

Honest limits: a value the game computes while it runs (from a car's stats file, a level script, a menu setting) is not in the ELF. Then you find it in RAM while playing and change the code or the file that sets it. Units are rarely obvious: 9.8 may be stored as 980, 0.163 (per frame) or 588 (per second squared at 60 fps). And frame-rate unlocks are often more than one number.

${CLAUDE_SKILL_DIR} below is this skill's folder (where this SKILL.md lives).

python3 "${CLAUDE_SKILL_DIR}/tune.py" scan SLUS_203.12 --value 9.8              # data floats + lui/ori/mtc1 constants
python3 "${CLAUDE_SKILL_DIR}/tune.py" scan SLUS_203.12 --value 9.8 --tol 0.05   # a wider net
python3 "${CLAUDE_SKILL_DIR}/tune.py" fps SLUS_203.12                           # 1/60, 1/30, 60, 30, PAL 50/25
python3 "${CLAUDE_SKILL_DIR}/tune.py" patch SLUS_203.12 --addr 0x0034A2C0 --float 12.5

Flags: --json on all three, --limit N, --place 0|1|2 (pnach place; the default is 0 for data, 1 for code), --exact (refuse rather than round when a lone lui cannot hold the new value).

What it reads and writes

file	what
the game's main ELF	read only: data words, code, sections, $gp
stdout	hits, the instructions around them, pnach lines, TOML blocks, the override write
nothing else	the user (or /console-mod) puts the lines where they belong

How a float hides in a PS2 ELF

form	looks like	scan reports	patch prints
a word in data (.data, .rodata, .lit4, .sdata)	0x411CCCCD = 9.8	DATA, plus the lwc1/lw that read it (through lui or $gp)	one pnach line and the override write /console-mod bakes in at load
built in code	lui $v0, 0x411C + ori $v0, $v0, 0xCCCD + mtc1 $v0, $f12	CODE with the instructions around it	two pnach lines (new lui and ori words) and two TOML instruction patches
lui + addiu	the low half is sign-extended	CODE	the high half is adjusted for the carry
a lone lui	values with a zero low half (1.0, 0.5, 12.5, 60.0)	CODE	one word; a value needing a low half is rounded to the nearest one it can hold (said plainly, exit 1)
set at run time	zero-filled BSS, heap	nothing in the ELF	a place 1 pnach line and the /console-mod frame-hook route

Float encodings, unit tricks and the Ghidra and PCSX2 steps are in reference/float-hunting.md.

The method

1. Name the feel and guess the number. "The car is too slow": top speed, acceleration, a drag factor. Ask what the game shows (a speedometer, a jump that clears two crates). Start from a value you can see.
2. Scan. tune.py scan <ELF> --value N. Too many hits: narrow by section (physics constants live in .rodata/.lit4 or in code next to mtc1), by the readers (one lwc1 in a function Ghidra calls UpdateCar beats 40 readers), or by a second related value nearby. None: widen --tol, try other units, or go to step 3.
3. Find it while playing (when the scan cannot): PCSX2's debugger memory search for the float, change it in game (jump, brake), search again; then a write breakpoint on the address shows the code that computes it, and that code's constants are what you tune. With GhydraMCP (optional, see /console-reverse) ask for the function's xrefs and decompile it.
4. Change it in PCSX2 first. tune.py patch <ELF> --addr ... --float ... prints the pnach lines. Put them in the game's pnach (/console-mod pnach.py crc names the file), enable, play. One value at a time, write down what changed.
5. Bake it in with /console-mod: code constants go in the game's TOML (patch prints the [[patches.instructions]] blocks; re-run ps2_recomp), data constants go in a game override (pnach.py override on the pnach, or paste the printed Ps2FastWrite32 line into an override.py module).
6. Playtest with /console-tester, then play the part of the game it touches. A shared constant (patch warns when several instructions read it) changes everything that reads it.

Typical targets

feel	look for	note
top speed, acceleration	the max-speed clamp and the per-frame add	often per frame: divide km/h by the frame rate
gravity, jump height	a negative per-frame velocity add, the jump impulse	jump height grows with the square of the impulse
grip, friction	a multiplier just under 1.0 (0.95, 0.98) applied every frame	small changes are large
damage	integers more often than floats: find them in RAM, see /console-mod	tables live in data
camera FOV	a float near 0.75 to 1.3, or a focal length near 1.0 to 2.0	/console-graphics widescreen.py scans the aspect ones
frame rate	tune.py fps; the vsync wait count in the main loop	read the caveat below

Frame rate, plainly: fps lists candidates, not answers. Many games pace frames with a vsync count (wait 2 vsyncs for 30 fps), an integer the scan cannot see. A 60 fps unlock also needs the game's logic to scale by the frame time: if movement, physics or animation are counted per frame, doubling the frame rate doubles the game speed. Test in PCSX2 first.

Guard rails

1. Bring your own game. Only a game the user owns, dumped from their own disc. Never download or look for ISOs, ELFs or BIOS files, never ask for them. PS2Recomp needs no BIOS.
2. Nothing from the game gets published. Share the pnach lines, TOML patches and override files. Never the ELF, the disc or the generated runner/*.cpp.
3. Not affiliated with Sony. PlayStation is a trademark of Sony Interactive Entertainment.
4. The tool only reads. It never edits the ELF, the TOML or the runtime: the user decides what gets applied, PCSX2 first. Change one value per test.

Hands off to

• /console-mod to bake a tested value into the port (TOML or override).
• /console-graphics for camera aspect and widescreen.
• /console-tester to playtest the change and check nothing else broke.