In the emulator

The emulator here is not for taking captures: it is for checking that what we say is true. The pictures on this site are drawn by Python running the cartridge's own steps, and the emulator is what says whether those steps are read right.

Starting it

openmsx -machine Philips_VG_8020 -cart soccer.rom

It is a 32 KB cartridge with an "AB" header and a single entry point, so it starts on any MSX1 with 8 KB of RAM.

Dumping the VRAM

make vram

That does three things:

1. launches openMSX with tools/omsx_vram.tcl, which sets not one breakpoint: the dumps are scheduled on emulated time, which is the only thing that does not choke the emulator;
2. at seven moments dumps the 16 KB of VRAM, the eight VDP registers, the 4 KB of working RAM and a screenshot;
3. compares the dumps against what tools/graficos.py builds, byte for byte, with tools/coteja_vram.py.

The script has a 240-second watchdog on real time: a broken script cannot leave the emulator hanging.

What the comparison says

titulo   COLOUR 0    PATTERNS 0    NAMES 0
campo    COLOUR 0    PATTERNS 0    SPR PATT 0
         MAP at 0xE600, 80x23:   2 of 1840
         WINDOW of 23x32:       44 of 736, and 42 are player patches

The title screen comes out identical across all three tables. On the pitch, the three graphics tables too, and the differences that remain are explained:

• the two map tiles are the two goalkeepers, which do not come in the compressed block: they are stamped when the play starts;
• of the 44 in the window, 42 are the 3x3 patches of the players who happened to be on screen at that moment, and the other two are those same goalkeepers.

The comparison deliberately leaves out the sprite attribute table —it changes every frame— and tiles 0x5C to 0x63, which the match rewrites as it runs to stamp the patches. That the pitch map uses none of them —its tiles run from 0x01 to 0x58— is what makes it possible to draw the whole pitch without playing the game, and there is a test watching it.

The eight registers, checked

The table at 0x4889 says 02 E2 0E 7F 07 76 03 E4, and the emulator returns exactly that on the start-up screen. During the match only R7 changes, to 0x00: the pitch's backdrop is black.

Looking at the RAM

The dump includes the 4 KB from 0xE000 to 0xEFFF, and the whole state of the match can be read there: the two kit palettes at 0xE051 and 0xE056, the twelve pieces from 0xE100, the pitch map at 0xE600, and the four strides per frame at 0xE06A-0xE071. At level 1 they come out as 0x0100 and 0x0150 for the human's side and 0x00E0 and 0x0130 for the machine's, which is what the table at 0x57EF says.

One caveat

tools/omsx_vram.tcl crosses the menu by pressing the space bar at fixed times. If Konami changed its mind, or if a slower machine is used, the dumps can land on a different scene: each info_NN.txt carries the scene and the sub-state written down, so it shows up straight away.