SwinSID and Dropzone. Bizarre.

[oracle_jedi]

So I picked up a scrap C64 a while back, and was able to bring it back to life with a new PLA and a new SID chip. 

 

Since the prices of SID chips are insane, I used a SwinSID.   I read up on the limitations, it doesnt support paddles, it sounds a little different, but that was all fine.  It did what I needed.  And it seemed to work great.

 

Then I converted the 64 to PAL to play those PAL-only games including Dropzone.  I love Dropzone on the Atari 8-bit, and I wanted to try the 64 version.

 

But something was wrong.  The scientist explorers wandering the planet surface were all bunched together in one spot.  The star background didn't scroll right.  And when I hit an alien, instead of the expected glorious explosion, the debris flew off in 4 distinct directions - up, down, left and right.  

 

I tested the image on VICE, and on VICE it all worked as expected.  But on the physical 64 is was buggy.  I suspected I had a bad PAL VICII chip and put the unit away until I had the energy to investigate.

 

Well tonight I did.  And I replaced, just as a test, the SwinSID with a real SID chip.  And lo and behold Dropzone now plays flawlessly.  Exactly as it does on VICE.

 

Is this a known issue?  Is this just my C64?  I think its a Rev D motherboard.  Originally NTSC.  I thought the SID was only for sound generation and reading the paddle controllers?

 

 

 

[hofster]

Just guessing here because I have no knowledge of SwinSID internals but it sounds like the game is using functions of the SID chip for randomization. Functions that for some reason behaves differently in the SwinSID.

As you say, some functions are missing on the SwinSID. Analog controllers of course, but also audio input.

I hope someone has a better explanation to how this affects the game in question.

[+OLD CS1]

8 hours ago, hofster said:

sounds like the game is using functions of the SID chip for randomization.

The SID's random number register pulls from the third voice's noise generator.  My understanding is the original SwinSID's randomization is an issue and not quite so random, and the SwinSID Ultimate produces better randomized numbers.

 

Edit: Check this out: https://ilesj.wordpress.com/2016/04/24/swinsid-ultimate/

 

If I read this correctly, it looks like the third voice registers are not readable in the original SwinSID, which would tend toward your issues.

[hofster]

1 hour ago, OLD CS1 said:

If I read this correctly, it looks like the third voice registers are not readable in the original SwinSID, which would tend toward your issues.

This is also an interesting note about randomizatiom on the SwinSID Ultimate compared to the SwinSID:

Quote

proper 23bit noise-waveform calculation –> better “random” numbers

That indicates the SwinSID offers some randomization but that it isn't perfect because the Ultimate is "better".

[oracle_jedi]

Thanks @hofster and @OLD CS1 

 

Really confused me for a long time, but this does make sense.   I have a local lead on a genuine SID replacement, so I am going to pull the SwinSID and put in the spares box.

 

[carlsson]

Aren't SwinSID and SwinSID Ultimate almost two different products?

 

But yes, the lack of random number generation is known. Try e.g. Paradroid with the SwinSID for very weird behavior.

[+OLD CS1]

1 hour ago, carlsson said:

Aren't SwinSID and SwinSID Ultimate almost two different products?

From different producers?  I have no idea -- I have not kept up with such details.  I suppose the Ultimate could be considered a different product being it has essentially three processors (not technically correct, I know,) readable registers, and a slew of other proper SID features.

[Mayhem]

The random number function was my first thought, and I see everyone else has the same opinion!

 

If you're going for a replacement, FPGASID is the recommended choice, if you can't afford that then ARMSID.

[eightbit]

For my money I'd go with an ARMSID. I've not experienced any compatibility issues with it at all, and the software and firmware upgrade process is quite awesome.

[R.Cade]

The SwinSID ignores reads, so you are just getting bus noise or pullup/pulldown behavior when you read anything there. Unfortunately it's not the same kind of random that a lot of programs need.

 

 

[hofster]

This also causes highly erratic pointer movement in programs that support a mouse, like the desktop environment of The Final Cartridge. It's totally unusable with a SwinSiD. It would have been so much better if it had returned somed fixed value.

That desktop environment wouldn't have been much less unusable either way but still...

[Mayhem]

Yeah I think I saw a couple of report issues when people were trying to play the Eye of the Beholder port.

[carlsson]

A new SID replacement just dropped, the KungFuSID: https://github.com/Sgw32/KungFuSID

[hofster]

Yes, I've been running that one for a couple of months and there have been some real improvements lately.

It still doesn't have analog support but at least it doesn't generate jitter the same way the SwinSID does.

I haven't tested it with the games in question so I don't know how well the ramdomization works.