In the emulator

The pictures on this site do not come from the emulator: tools/graficos.py draws them from the bytes of the ROM. The emulator is used for the opposite, which is checking that those pictures are true.

Dumping the real VRAM

"C:/Program Files/openMSX/openmsx.exe" -machine Philips_VG_8020 \
    -cart pingpong.rom -script tools/omsx_vram.tcl

The script lets the game run and, at seven moments spread over the startup and the match, dumps into work/omsx/:

• the 16 KB of VRAM exactly as the VDP sees them
• the eight registers, which say where each table is
• the variables that say what was being drawn: scene, subscene, mode, level, game, rally phase and both scores

It sets no breakpoints at all: the dumps are scheduled on emulated time, which is the only thing that does not choke the emulator. And it carries a real-time watchdog, so a broken script cannot leave it hanging.

Comparing

python3 tools/coteja_vram.py pingpong.rom work/omsx/vram_01.bin logotipo
python3 tools/coteja_vram.py pingpong.rom work/omsx/vram_03.bin titulo
python3 tools/coteja_vram.py pingpong.rom work/omsx/vram_04.bin nivel

It compares the four tables -colour, patterns, names and sprite patterns- byte for byte, and says in which and in how many bytes they differ. What comes out today:

scene	bytes different out of 16,384
logo	0
table with the menu	0
title	1

The one byte left is the eighth of the small "KONAMI" at 0x3868: the dump catches that animation half-way through, it is not a format error.

Sprite attributes are not compared: they change every frame. What is compared is the scenery, which is what graficos.py claims to reproduce.

What the registers confirmed

info_00  regs 02 E2 0E 7F 07 76 03 E4   scene 0, subscene 2
info_02  regs 02 E2 0E 7F 07 76 03 E0   scene 1, subscene 3
info_04  regs 02 E2 0E 7F 07 76 03 E0   scene 3, subscene 5

Three things at once:

• the eight registers are the ones the table at 0x47D6 says, with R3=0x7F and R4=0x07, that is, VRAM the other way round
• R7 changes from 0xE4 to 0xE0 between the logo and the player selection
• and in the demo, level 3, which confirms the fixed value set by 0x40A9

Playing it

With any MSX1 emulator and the cartridge in page 1. With openMSX:

openmsx -machine Philips_VG_8020 -cart pingpong.rom

Player 1's keys are the arrows and the space bar; player 2 has their own keys, spread over four rows of the matrix, and both joystick ports work too.