Hi, I think you can try out using speaker.drv from Windows 3.1 era and see how far things go.
To my understanding both Covox and PC Speaker are being CPU-driven, there's no dedicated hardware, no DMA.
Interrupts might might be supported, depending on the driver version, so the mouse cursor doesn't feeeze during playback of PCM samples.
But merely as long as the audio buffer hasn't been running out.

Last time I tried it - probably 30 years ago - it only allowed to play short PCM samples in RAM, and didn't allow to do anything else while playback.
Same as the PC Speaker WAVE driver.

So, before you make a Covox, you can try the PC Speaker drivers (I think there's more then one), and see what's possible with non-DMA sound devices...

The problem with pc speaker is that it is 1-bit device, or something. So I am pretty sure that it will be very demanding. But covox is 8-bit device. So I want to know if it is possible to use it as a sound device with games like quake3.

PlaneVuki wrote on 2024-05-07, 10:53:

The problem with pc speaker is that it is 1-bit device

modern fancy Class D amplifiers are also 1bit, so were CD players with 1-bit Sigma Delta DACs 😀

PlaneVuki wrote on 2024-05-07, 10:53:

So I am pretty sure that it will be very demanding. But covox is 8-bit device. So I want to know if it is possible to use it as a sound device with games like quake3.

no, Covox requires CPU to stop everything its doing at precise time intervals to program value into LPT port. Not only is it very cpu intensive, but also tight timings are highly problematic in multitasking OS.

This is why Disney came up with Disney Sound Source - Covox with 16 8-bit words FIFO allowing for random timing burst data delivery Reversing the Disney Sound Source

I just had a look at some code for PCM playback via PC Speaker and Covox...

There shouldn't be significant difference in CPU load between those two devices:
- timer interrupt frequency is the same
- for Covox, the interrupt routine simply outputs a Byte to the LPT port
- for PC Speaker, the interrupt routine outputs to the $42 port the following: Byte shr 1 + 1

Yes, Covox may provide better sound quality than PC Speaker, but can't make it easier for the CPU.

Grzyb wrote on 2024-05-07, 18:35:

I just had a look at some code for PCM playback via PC Speaker and Covox... […]
Show full quote

I just had a look at some code for PCM playback via PC Speaker and Covox...

There shouldn't be significant difference in CPU load between those two devices:
- timer interrupt frequency is the same
- for Covox, the interrupt routine simply outputs a Byte to the LPT port
- for PC Speaker, the interrupt routine outputs to the $42 port the following: Byte shr 1 + 1

Yes, Covox may provide better sound quality than PC Speaker, but can't make it easier for the CPU.

So does this mean that for the same sound quality, covox is much less load on cpu than pc speaker?

Perhaps in that code the programmer kept loads equal for both?

PlaneVuki wrote on 2024-05-08, 06:04:

So does this mean that for the same sound quality, covox is much less load on cpu than pc speaker?

No.
Can't achieve the same quality.
Covox is a normal DAC, and - properly built - can be as good as any 8-bit sound card.
But I've never heard PC Speaker playing PCM at comparable quality.

Perhaps in that code the programmer kept loads equal for both?

Well, that's possible.
There's more than one technique for PCM playback on PC Speaker.
Obviously, one of the techniques involves timer interrupt frequency equal to the sampling rate.
But I believe I've seen some other code, using 8 x greater frequency.