STE Blitter bus arbitration glitches, BG needs small cap ?

[sporniket]

Hello, seen on Atari-forum, someone on the german forum observed some spikes on BG preventing the Blitter to takeover the bus (also, the spikes happens more often with an accelerator board), and solved that with a small capacitor (47pF, the location change depending whether one has a separate Blitter or a Blitter integrated in the MCU).

The original thread in german forum

The thread on atari-forum

[exxos]

I've only had a very quick look. But they do not appear to have posted any programs to actually specifically test for this problem ?

But also it is important to remember that resistor pack P100 was updated to 1.2K (Atari's own fix) which has some pullups on the bus grant signals. It does not appear to mention about various motherboard revisions either.

[Steve]

I've only had a very quick look. But they do not appear to have posted any programs to actually specifically test for this problem ?

But also it is important to remember that resistor pack P100 was updated to 1.2K (Atari's own fix) which has some pullups on the bus grant signals. It does not appear to mention about various motherboard revisions either.

I think the fix came about from two investigations, one which is here to do with a demo development: https://www.atari-forum.com/viewtopic.p ... 4&start=25

The other was a new accelerator development by the ThunderStorm team for the STe. Between these two separate investigations came this fix, from what I can see.

[exxos]

I think the fix came about from two investigations, one which is here to do with a demo development: https://www.atari-forum.com/viewtopic.p ... 4&start=25

I'm confused as to what is going on with what. To many conversations going on about various things. I don't have much time to read through it all unfortunately.

I remember replying to the video www.youtube.com/watch?v=ZRU6bvv_gJU&t=86s in the comments. It popped in my YT feed a couple weeks back. So I tested the 2 shifter revisions. One caused the wrap-around effect, the other didn't. So don't know what that has to do with bus grant issues on a accelerator.

Anyways, If someone wants me to specifically test a program on my STEs to see if I have this fault and the capacitor fix fixes it. Then I can do that at least.

[exxos]

I had a quick look through that thread again. Someone posted a demo https://www.atari-forum.com/viewtopic.p ... 45#p438145

So I downloaded it and tried it on both shifter revisions and basically looks fine other than what appears to be something like four black pixels towards the bottom right, which seems to wrap around for maybe 100 pixels which are then the wrong colour. It is barely noticeable but it is rocksolid consistent.

I tried with a stock STE (Later board with integrated blitter) and also then inserting my simple 32Mz booster (running 8Mhz mode) and made no odds either.

1.JPG

I tried 33pF and 100pF caps as mentioned on the German forum and it made no difference at all.

As also mentioned I replied to the video where pixels had the infamous "wrap around" issue. But that was relating to shifter IC versions.

One video shows screen wobble down the left-hand side. I have seen that on the STFM in the video circuit was failing. On the STE video faults can be down to parity simms or bad connections on the shifter etc.

So as it stands I cannot replicate the problem, though I'm not really sure what the problem is supposed to be exactly.

[sporniket]

Thanks for your time :)

[Badwolf]

I've had a chat in the past where ground and power lines were also mentioned in relation to an STE integrated blitter bug. Suggestion was running auxiliary ground and power lines to the area near the combo chip and adding a 1uF cap across the existing decoupler.

I've not actually got around to trying that as I've not done any DSTB1 work for a while.

BW

[exxos]

I've had a chat in the past where ground and power lines were also mentioned in relation to an STE integrated blitter bug. Suggestion was running auxiliary ground and power lines to the area near the combo chip and adding a 1uF cap across the existing decoupler.

I really do wonder how much of the metal shielding Atari was using as a actual ground. While these boards indeed really dislike being manhandled. So malfunction anyway. I wonder how many "faults" become attributable to not been clamped down on the shielding any more.

[Oldskool]

Also tried the mod. Indeed no effect on a stock ste. Probably something they need for the Twister.