Adventures in PC Emulation

Writing a cycle-accurate emulator for a computer system is more than just understanding all the CPU instruction timings. A computer is a complete system with peripherals, interrupts, IO bus signals, and DMA. All this comes with an array of different timings and quirks. When software like Area 5150 is written that requires perfect cycle timing, it can be a challenge to provide the level of accuracy needed for the software to function. Area 5150 in particular requires precise coordination with the CGA's CRTC chip and timer interrupts to begin the end credits demo effect at precisely the right time. Getting this right is crucial to whether the demo effect produces this: Artwork by VileR Or this: It would be very handy then if we could somehow peek into the operation of the system while it was running and understand how all these parts interact.  As it turns out, we can! This process is typically referred to as 'bus sniffing', and there's a lot of a technical information ou...

The Book8088 is an interesting little machine. It is essentially a 1980's computer in a laptop form factor. With apologies to Sergey Kiselev , whom the manufacturers of the Book8088 did a little dirty , I couldn't resist ordering one myself to tinker with.  The Book8088 is trying hard to basically be compatible with the original IBM PC, containing some of the same or equivalent chips. It's natural to want to put it through its paces, and one of the best tests for IBM PC compatibility has to be the 8088MPH demo .  If 8088MPH will run we must be operating pretty darn close to the original.  Looking at the specs of the Book8088, there's good reason to be optimistic.  The machine supports a real 8088 CPU.  Even better, there's a socketed CRTC chip, so the complex CRTC abuse the demo performs doesn't need to be emulated in any fashion. My Book8088 came with an NEC V20 CPU.  This CPU is a lot faster than the 8088, we'll need to replace it: Additionally, the ...