CV64/3D, P96 and A4000 with strange graphical glitches

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Don't Panic. Please wash hands.
  • Hi,


    I'm just wondering if anyone else have had this issue. I have a CV64/3D that's been working perfectly for years in my A1200 ZIV busboard but today I moved it to my A4000 (for those sweet ZIII-speeds) but I get these strange graphical glitches in >800x600 resolutions (800x600 and below are perfect). The picture looks fine when everything is still but as soon as I start moving things around I get these odd flashes with graphical garbage made up of stuff that's on screen. It remains as long as I'm moving a window or resizing. NOT when moving the mouse or the picture is still.


    I've tried reducing clockrate but it does not appear to make a difference. I don't have other RTG cards to test, but there is no other indications that I have a problem with the busboard or motherboard. Both were recently overhauled and recapped and has been working perfectly. Only my CV64/3D is glitching.

  • This sounds like a flaky power supply (high ripple on 5V) or ageing RAM chips on the card. You also might want to check the daughter board connection (remove, clean and re-insert) and see if the board has been overclocked: 25MHz is the maximum you can do with any Buster version. Anything above that is pure luck.

  • Thanks for the reply Jens. I've got the newest buster and the board has not been overclocked. While cleaning connections and testing I tested higher colordepths as well (I normally only use 8bit) and 16bit and 24bit work perfectly no matter the resolution. Odd?

  • The S3Virge chip has two different methods of composing the picture. One is the old-fashioned VGA mode, the other is going through a so-called "stream processor". For (so far) unknown reasons, picture composition with the stream processor is more robust (my personal guess is that the VGA part was rarely used and the stream processor is properly pipelined).


    Unfortunately, the stream processor can't do everything that the standard VGA mode can do: It does not allow splitting screens, can't do double-scan and no double-clock modes. For that reason, the stream processor is switched off by the driver when needed.


    For double-clock modes, the VGA chip reads two 8-bit values at a time (same amount of data as with 16-bit modes), but the DAC will produce two 8-bit pixels from the data (instead of a single 16-bit value). This is something that the stream processor can't do. And here's where the chip may have difficulties, as this is two CLUT-lookups per memory access, which might be pushing it for that generation of chip technology.


    Double-Clock is only available for 8-Bit modes. It will be switched on starting at 85MHz pixel clock with the current driver. There may be a possibility to push this threshold a little, maybe by configuring the Fifo in a different way or by activating double-clock a little later. However, there's very little we can do without hardware. Remember that we've implemented this "almost blind". I used to own a CV64, but I have given it away to someone who sold it shortly after. If someone is willing to part with an S3 Virge-based Z2/Z3 card for a fair price, I'd be willing to buy it.

  • I used to own two of these cards, but sold one to afford a Cyberstorm 040. I cannot part with the only RTG-card I have, but I'm sure there are users out there (with more lavish hardware collections) who would not mind selling one at a good price, especially when it goes towards actual development. I mean, people are giving EXPENSIVE hardware away to youtuber's just for a mention in a "donations"-video..


    I would be happy to send you my card as a loan, however, but I understand if that's just a bit too complicated and risky.

  • Here's a driver that disables the blitter for those modes that don't use the stream processor - in an attempt to find the part of the chip that causes the glitches. Please report back if it improves anything (and yes, it's expected that some things are slower without the blitter).

  • Here's a driver that disables the blitter for those modes that don't use the stream processor - in an attempt to find the part of the chip that causes the glitches. Please report back if it improves anything (and yes, it's expected that some things are slower without the blitter).

    I gave it a try and yes, this appears to solve the issues, and as you noted: slow things down a little. Still an improvement overall :) Thanks!

  • I can still reproduce the issue, albeit only in the highest resolution 1280x1024x8

    Here's where I'd start measuring voltage on the 5V rail: At highest frequency, CMOS circuits tend to get more stable if they are operated at nominal voltage. However, the old power supplies in our Amigas often haven't been serviced in 30 years and may have dry electrolytic caps, resulting in high ripple and as a result, lower usable voltage.


    It is likely that with fresh electrolytic caps and voltage adjustment according to the load in your system, these glitches go away.

  • Done ;)

    So i assume there is A Card on the Way to iComp?!?

    On the other hand i would be willing to lend my card free of charge and taking the risk.

    I talked to thor on A1k and offered to lend my A4000 + GFX Card, he metioned I may should contact iComp first.

  • So i assume there is A Card on the Way to iComp?!?

    Not yet - I did have an offer from the US, but I was hoping to buy a card from "not so far away". I'd prefer owning one of these cards, as only this will ensure future updates and proper testing. Programming without a test bed is about the worst situation you can be in, and I'd like to avoid that.


    To my knowledge, Thor wouldn't need the whole computer - just the card would be sufficient.

  • Since this is my only CV64 3D selling is a bit unfotunate..... i got lucky not selling my soul.


    Sending the Card to thor for a a year or so might help.


    I will let him Know that my offer is still valid, then you or he may decide if you take it.

    Untli then i might find a second one.

  • I can report that after upgrading to P96 3.10 these issues went away, getting a stable image even in 1280x1024.

    Not a PSU problem after all.