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update PC speaker doc

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tildearrow 2022-06-03 01:32:56 -05:00
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papers/doc/7-systems/pcspkr.md
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40 years of one square beep - and still going! Single channel, no volume control...
# real output
so far this is the only system in Furnace which has a real hardware output option.
to enable it, select file > configure system... > PC Speaker > Use system beeper.
be noted that this will only work on Linux as Windows does not provide any user-space APIs to address the PC speaker directly!
you may configure the output method by going in Settings > Emulation > PC Speaker strategy:
- `evdev SND_TONE`: uses input events to control the beeper.
- requires write permission to `/dev/input/by-path/platform-pcspkr-event-spkr`.
- is not 100% frequency-accurate as `SND_TONE` demands frequencies, but Furnace uses raw timer periods...
- `KIOCSOUND on /dev/tty1`: sends the `KIOCSOUND` ioctl to control the beeper.
- may require running Furnace as root.
- `/dev/port`: writes to `/dev/port` to control the beeper.
- requires read/write permission to `/dev/port`.
- `KIOCSOUND on standard output`: sends the `KIOCSOUND` ioctl to control the beeper.
- requires running Furnace on a TTY.
- `outb()`: uses the low-level kernel port API to control the beeper.
- requires running Furnace as root, or granting it `CAP_SYS_RAWIO` to the Furnace executable: `sudo setcap cap_sys_rawio=ep ./furnace`.
real hardware output only works on BIOS/UEFI (non-Mac) x86-based machines! attempting to do this under any other device **will not work**, or may even brick the device (if using `/dev/port` or `outb()`)!
oh, and of course you also need the beeper to be present in your machine. some laptops connect the beeper output to the built-in speakers (or the audio output jack), and some other don't do this at all.
# effects
ha! effects...