QBX: PC Speaker Emulation

I'm excited by this. 🙂

Getting closer to running NIBBLES. The latest advancement: PC speaker sound emulation.

You might think, looking at this, that it's not _really_ PC speaker sound emulation, it's QBASIC PLAY statement emulation, right?

Wrong 🙂

Behind the scenes, there's a simulated 8253 timer chip. Its Timer 2 configuration is linked to a simulated 8042 keyboard controller chip (well, this last one is a bit of a stretch, because it only cares about the two speaker control bits). (For performance reasons, it simulates frequencies and ticks instead of communicating actual raw ticks.)

The function in charge of playing a note as part of a PLAY statement does so in a manner that reconfigures the 8253 to generate the target frequency. The sound you're hearing is the raw square wave resulting from the simulated output from the timer chip. Woohoo!