A day at the races - CHIP-OTTO version 0.4 (ZX Spectrum Next)

I'm not talking about the album by Queen or the film by the Marx Brothers, but about VIP Animal Race. It is a fun game for CHIP-8, programmed by Brian Hastle. Five different animals race against one another and you have to bet on the winning one. I don't usually like to gamble, but today I made an exception :)

When, at the beginning of the 90's, the CHIP-48 and SUPER-CHIP interpreters were coeded for the HP 48SX graphing calculator, some incompatibilities (often referred to as "quirks") with the original CHIP-8 interpreter were introduced. So, some games could not run on many modern interpreters, whose implementation is based on the SCHIP documentation. VIP Animal Race is one of these.

Today I finally overcame this problem in CHIP-OTTO, my CHIP-8/SCHIP interpreter for the ZX Spectrum Next, by adding a new bitmask configuration called Legacy compatibility flags.

By setting some of the flags in the game configuration file, the way the interpreter executes some opcodes can be changed; in particular:

• Bit 0: Shift operations (opcodes 8xy6, 8xyE):
  • 0: Vx is shifted 
  • 1: Vy is shifted and the result is stored in Vx
• Bit 1: load/store operations (opcodes Fx55, Fx65): 
  • 0: I is incremented (I = I + x + 1) 
  • 1: I is not incremented
• Bit 2: memory overflow in opcode Fx1E
  •  0: if I > 0xFFF VF is set to 1; otherwise to 0
  • 1: VF is not altered

So, today I was finally able to run VIP Animal Race in CHIP-OTTO, as you can see in this video:

You can get your free updated CHIP-OTTO copy which includes the configuration for VIP Animal Race from: https://retrobits.itch.io/chip-otto.

Play responsibly!