It carries Konami's hidden mark

At the end of the ROM, behind the filler, Konami hid in many cartridges its catalogue number and the title in katakana; Manuel Pazos (@ManuelPazosMSX) found it. Here it is: the last eleven bytes from 0x7FF5 are the title reversed, its length, the 18 of RC-718 in BCD and the 0xAA that closes it.

One dead loop, and the whole machine in the interrupt

INIT hooks the interrupt to 0x4051 and falls into a jr to itself. From there the main program does nothing: each frame the interrupt reads 0xE000 (the state, 0 to 8), jumps through a table of nine handlers, and inside each one the byte 0xE001 splits the sub-states with djnz chains.

The road is a table of shapes indexed by curvature

There is no geometry: 0x68D0 reads 0xE074 —the curvature and position of the track— and indexes the table at 0x767C to pick which road shape to draw. The stripes move toward the player by scrolling a buffer (0x707A) at the speed's pace, and the depth scaling of the roadside objects comes from the tables at 0x6CD5.

Twelve stages from eight composers, and two of them at night

0xE060 runs from 1 to 0x0C and with it, through the table at 0x481A, the background composer of each stage is chosen: eight routines cover the twelve, and stage 12's composer calls stage 5's. The parameter 0xE061 (table at 0x4372) is a bit field holding what is particular about each stage: bit 1 is the slippery snow, 0x01 the tunnel, 0x10 the storm and 0x08 the night. In the two night stages, 0x71AC runs a field of sixteen stars across the sky, at pixel precision and at the pace of the car's speed.

The sound is the house's three-channel player

The engine at 0x5FB7 walks three fourteen-byte records (0xE010), reads the melodies with its command interpreter and writes the PSG through the BIOS. It is the same player framework Konami spread across its MSX cartridges; 0x5ED9 starts a melody or an effect by its number, checking priority first so it does not step on what already plays.

The player car is six sprites, and rivals collide by depth

The car is assembled from six sprites (template at 0x66E2) that 0x65FA repositions every frame from the wheel. The three rivals keep their records at 0xE138/48/58; 0x7C34 sorts them by nearness before drawing, and 0x7F89 halves your speed when you hit one.

An opponent has no path of its own

0x7CCB was in the listing as the impact, and it does not touch your speed: the only thing it writes is the opponent's position, to which it adds (the opponent's speed − yours) / 16. In a 45-second race without a single hit it ran 1329 times. And 0xE09C, which the listing called the opponent's colour, is its speed: forced to 0 you eat all of them, forced to 255 they all get away. The arithmetic redone in Python reproduces 102 of 102 cases read inside the routine itself.

There is no pyramid drawn anywhere in the ROM

In the desert the road does not scroll: 0x707F diverts the scroll to SUBEN_PIRAMIDES. And there is no pyramid stored anywhere: there is a 32-byte window at 0x7351 —sixteen zeros, then the triangle— that slides one step each time 0xE071 reaches one of the sixteen thresholds at 0x7371. The right half of the pattern is the left one through INVIERTE_BITS, the same trick as the rival car.

An opponent coming closer changes material on the way

It does not grow: it stops being sprites and becomes screen. Table 0x7D94 gives twenty steps, and the two low bits of each pattern say how many sprites light up —one far away, two closer, and four in two overlaid colour layers, which is how you paint a two-colour car out of sprites that only take one colour each—. When byte 0 of the record drops below 0x28, 0x7B21 writes Y = 0xE0 into all four sprites and RIVAL_MEDIO (0x7AD1) repaints it with twelve tiles of the name table.

And of those twelve, the cartridge only stores half: 0x2A is 0x24 with its bits reversed, and so on up to 0x2E. The other half is put there by DESC_DOBLE (0x44B0), which runs the same block twice and sends the second pass through the relocated core at 0xE310, which falls into INVIERTE_BITS.