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Comment by geocar | Hacker News Reader

> I don't know how IT got PC speaker emulation down, but they did IIRC through some sort of high precision timer magic such that it didn't need a sound card per se

You can check!

https://github.com/jthlim/impulse-tracker/blob/main/SoundDri...

No magic I can see.

> basically by copying whatever glyphs would be under/around the mouse cursor to each sacrificial replacement glyph and dynamically drawing a fraction of a mouse cursor over each, and then writing the magic text chars to the text buffer.

Exactly correct.

> legacy FreeBSD text console

I never knew that. I wrote one for Linux because I like the visual feedback of what row I'm on by the mouse cursor changing.

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Cool beans. "Magic" isn't literal. No magic, any time. ;) It's also probably in one of my vintage PC programming books or vintage programming text file collection. It reprograms timer0 (the system timer) of the 8254 and chains the interrupt handler for IRQ 0 (interrupt 8), and then bangs data out the speaker port relatively fast compared to "dumb" beeps.

Text mouse cursor: I think I first came across this trick in the 1st ed of PC Intern.

Artifact on "normal" default VGA text mode 3: the right-most pixel is duplicated from an 8x16 source glyph is displayed as an 9x16 sprite on a 720x400 (pixels) hardware frame buffer, so the cursor trick periodically has a stair-step artifact when in-between characters. The pixel is duplicated so box and line drawing and other glyphs can be gapless, and it's 9 pixels wide as characters look better than squished into 8x16. The source glyph in the table remains 8 pixels wide because it's exactly one byte wide (1 bit per pixel), because 9 pixels would take up 32 more bytes in the standard glyph table (or 64 bytes more in a 512 character table). This won't happen in 8 pixel wide glyph modes like 80x50 X 8x8 (640x400 - mode 66h) IT uses.

TIL: Linux may have a text mouse console driver that works, I'm guessing, with a coordination between kernel settings and gpm.

It's an old/good trick. The linux kernel offers an ioctl to set the font tables, and has for years. I think the kms people want to remove them which is a little sad.

Until then you can also use a tool called SVGATextMode to set the registers and get 80x50 or even a 160x100. I still think text-mode is great. I don't know very much about FreeBSD; I last used OpenBSD almost 20 years ago. Before Linux my unix was Solaris or SCO.

These days, I have a tegra (nvidia arm64) system and it still has a x86 vga bios in there(!!!) so linux actually ships an x86 emulator to "read" the outb/w instructions. Amazing.

Cool. I really worry about emulation failing to have options to be faithful to real hardware limitations or faithfully reproduce bugs and artifacts of particular steppings and versions. On real hardware, I/O port instructions often require delay cycles before other operations can proceed. VGA monitors had an overscan area that could be set to a specific color in the palette, which is rarely emulated. Video tearing is rarely emulated properly. Snow and garbage that happen between video mode changes or boot cycles too. And, where's the degauss button? ;-P

I remember FastTracker needed the overscan to tell you if you were in Edit mode or not (or I guess you could just try keyjamming). I think I saw someone announced a clone recently and I noticed they didn't implement that. Now that you say this I wonder if their only experience was in an emulator.

But we still have snow: remember rowhammer? Basically snow on purpose. So I'm not so worried that kids will lose knowledge of analog effects just because we don't have CRTs anymore.

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