7,882 bytes of code and 8,502 of data. 492 named routines, 1,368 anchored comments, 32.4% of the listing commented and no routine under 10%.
0x4010 is a whole frame of the game. It reads the VDP status, marks 0xE01D so nobody else touches the VDP behind its back, reads the controls, runs the sound — which plays on every frame, whatever else happens — and then, if there is a match on, the nine tasks of the frame, in order, from 0x4070:
0x6D12 swap the doubles pairs
0x555D give each player his frame
0x6E97 rotate the pairs between points
0x6B25 play the opponent
0x678D decide his shot
0x51FE move the ball
0x6ED2 the umpire's eyes
0x7932 award the point
0x7F56 put everyone back in place0xE0D9 spreads that work over frames: not all of it fits in one.
The cartridge does not store screens as VRAM dumps. It stores scripts.
Tile lists (0x43EA) are the simple one: each entry starts with its VRAM address in two bytes and then bytes that go to the data port, with 0xFE n b to repeat and 0xFF to close. Two 0xFF in a row close the list.
Scripts (0x445F) start with a block count, and each block carries a command:
0 raw bytes, with 0x11 n b to repeat
1 patterns by index into the table at 0x489D, eight bytes each
3 one address and then pairs of count and value
* one address, a repeat count, and a pointer to an eight-byte patternAnd a rule that runs through all of it: any counter at zero means 256, because the Z80 decrements before it tests.
A pose is five stacked 16x16 sprites. 0x5961 is a table of 58 entries; each points at a twelve-byte description — five pattern pointers plus one pointer to the five (y,x) pairs. 0x58A9 loads the patterns, 0x58D4 places them.
The sprite decompressor is 0x5932 and always writes 32 bytes, with one rule: 0x00 n writes n zero bytes, everything else goes through as it is.
There is no multiply or divide on a Z80, so the cartridge builds its own: 0x54AA shifts and subtracts eight times, 0x54CA shifts and adds sixteen, and 0x547E divides by counting how many times the divisor fits. The ball's flight is built out of those three.
Three channels, eleven bytes of state each from 0xE211. A tune is read by the high nibble of each byte: 0x1x duration, 0x2x volume, 0xDx vibrato step, 0xEx octave, 0xFx vibrato width, 0xFE up an octave, 0xFF end. Anything else is a note — high nibble the semitone, low nibble the duration — and the period comes from the twelve-entry scale at 0x7C5D, doubled once per octave.