heyspacebuck / pokepinball-romhack

Disassembly of Pokémon Pinball, modded for link cable stuff

Pokémon Pinball for Serial Peripherals

This is a fork of the Pokémon Pinball disassembly by PRET.

The original instructions for setting up the repository are at INSTALL.md.

From Rumble to Serial

In home.asm, options_screen.asm, and some of the files in engine/pinball_game/object_collision/, you can find lines like this:

ld a, $ff
ld [wRumblePattern], a
ld a, $60
ld [wRumbleDuration], a

The first value (0xff in this example) sets the intensity of the motor based on the number of high bits (so, 100% intensity in this example). The second value (0x60) sets the duration of the rumble, in frames (60₁₆ = 96₁₀, so at 60 fps this would be 1.6 seconds of rumble).

Before each of these sets of rumble instructions, I have inserted my own instructions:

ld a, $f6
ld [rSB], a
ld a, $1
ld [rSC], a
ld a, $81
ld [rSC], a

Writing a value to the rSB register and then writing 0x81 to the rSC register causes the game to transmit the rSB value over the serial cable. Setting rSC to 0x01 before setting it to 0x81 doesn't seem necessary, but that's how the "real" link cable instructions do it so I tried to put that in when possible.

Within the game there are a few different rumble patterns used that work out to 25% intensity, 50% intensity, or 100% intensity. And they run for either 1, 3, 4, 8, 64, or 96 frames. So, whenever a rumble event occurs, these new lines send that info out as a single byte for the peripheral to decode. Is it possible to transmit more than a single byte? Probably. But I haven't tried yet.

The Peripheral

When the game sends an instruction over serial, it puts out an 8 kHz clock signal. Data gets read on the rising clock edge. I've set up an Arduino Uno to read the data line on clock rising-edge interrupts, which I'll put in the repo unless I forget. Right now that Arduino doesn't do anything with the data it receives; the next plan is to drive a DC motor through a MOSFET, and later use it to control a Hitachi/Doxy magic wand.

I Am Not Good at Assembly

When building blue_stage_resolve_collision.asm, the linker(?) writes one particular jr instruction that is out-of-bounds (it tries to jump 128 lines, but the only valid range is -128 to 127). Instead of looking up ways to address this, I just commented out the ld a, $1 line. This might affect the rumble/serial when hitting the Pikachu on the Blue Table.

Every time I tried adding a serial-transmit instruction to red_stage_resolve_collision.asm, I received the error

ERROR: main.asm(81) -> engine/pinball_game/draw_sprites/draw_red_field_sprites.asm(569):
    Section 'bank5' grew too big (max size = 0x4000 bytes, reached 0x4002).

Instead of learning how banks work and stuff, I just commented out the original rumble instructions and it compiles now. So this means, if you somehow put this ROM onto a cartridge with a built-in vibrator, it won't vibrate on the Red Table. But the serial port will work.