Falcon IDE read failing at higher frequencies

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mikro
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Falcon IDE read failing at higher frequencies

Post by mikro » Wed Sep 19, 2018 7:24 pm

I'm aware that after this post all the remaining bits of my reputation and pride will be gone but hey, it's always better ask more experienced people. :-)

Yesterday I was *this* close to have my CT2 Falcon finished - various clever IDE solutions, everything tidy, fitting in the standard case etc. One of the last components to install was a small 44pin SD standalone adaptor (fits between the IDE connector and PSU!), basically PCB with an SD connector soldered to it.

And don't ask me why, I just mounted the thing (its rear side is very close to the PSU voltage wires) without any insulation. It didn't obviously touch, I did several experiments with it (finding the best position etc), so all in all it must have run at least two hours with breaks. And then, when everything was closed for good and working, after 10 minutes... bzzz... PSU gone (no, this time it wasn't yours Chris :)), SD adaptor gone, SD card gone (!) Fortunately there wasn't any explosion or smoke.

What most likely happened was a short circuit between SD adaptor (IDE) pins and +5V and/or GND (most likely +5V as crossing few pins to GND perhaps wouldn't do much harm). Well, apart from broken parts (PSU, adaptor, card) it looked the Falcon has survived. Until the next boot.

After countless tests I have found out that reading from IDE is corrupted by random bits if running in CT2's TURBO mode (i.e. accelerated CPU, Combel & SDMA). IDE writing is fine, floppy r/w is fine, SCSI r/w is fine. So this leads me to the conclusion that perhaps I didn't kill any important IC but most likely some passive component in charge of filtering IDE signal(s). So it happens to work in 16 MHz mode only by chance.

Have you ever experienced something similar? Where would you recommend start looking? First I was thinking the resistors leading to IDE data wires but perhaps that's stupid - if a resistor blew up, it wouldn't work anymore in 16 MHz. Of course anything between IDE and Combel (maybe DMA, too?) are the prime suspects but if I could narrow this down a little...

Petari
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Re: Falcon IDE read failing at higher frequencies

Post by Petari » Wed Sep 19, 2018 8:11 pm

Most likely Combel is damaged - injured, not killed.
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exxos
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Re: Falcon IDE read failing at higher frequencies

Post by exxos » Wed Sep 19, 2018 9:28 pm

If its working on a stock config, but not accelerated bus, then the bus is running to fast for it to be reliable.
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mikro
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Re: Falcon IDE read failing at higher frequencies

Post by mikro » Wed Sep 19, 2018 9:42 pm

exxos wrote:
Wed Sep 19, 2018 9:28 pm
If its working on a stock config, but not accelerated bus, then the bus is running to fast for it to be reliable.
But what could make it to run 'faster' ? And only for reading? It worked like a charm before the accident.

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exxos
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Re: Falcon IDE read failing at higher frequencies

Post by exxos » Wed Sep 19, 2018 9:54 pm

mikro wrote:
Wed Sep 19, 2018 9:42 pm
But what could make it to run 'faster' ? And only for reading? It worked like a charm before the accident.
You say yourself you are accelerating the CPU, so it will read the IDE bus faster... Assuming you now using a different SD card & adapter, just probably was a fluke combo of hardware which made it work before and not now.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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KyleB
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Re: Falcon IDE read failing at higher frequencies

Post by KyleB » Thu Sep 20, 2018 2:22 am

I would imagine mikro is sensible enough to have tested this thoroughly and confirmed that the symptoms he's reporting are accurate. He says he has, so believe him.

I've certainly never heard of the CT2 ballsing up the IDE as a normal behavior (honestly, would anyone buy one if they did?). Is the replacement PSU trustworthy?

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Re: Falcon IDE read failing at higher frequencies

Post by mikro » Thu Sep 20, 2018 6:53 am

Chris, that's a very pessimistic conclusion. ;-) That way the Nemesis, Phantom, CT2, CT60's bus acceleration would be just flukes, although from technical point of view it wouldn't be necessarily a lie.

Everything has been replaced for a new component, incl. the PSU (I was using Centuriontech's PSU due to its smaller size - I was heartbroken to realise that the SD adaptor doesn't fit with Exxos PSU but in the end you see, if it weren't for the adaptor...) so I'm pretty confident this is the final state of things.

So far I'm going to assume the Combel is fine (although Petari may be right - who knows what happens if you drive/short-circuit +5V on one of the IDExxx pins) and focus on two directions: clocks (there could be a damage from the +5V, esp. on the master clock crystal) and passive components (U25, IRQ pull down resistor, yes also those data lines resistors, ...). Fortunately, there isn't that many things between the CPU and IDE, there's no controller or some other logic involved, more or less CPU bus naked to the outside.

Btw thanks to the diagnostics I've had the opportunity to experience the true 90s - SCSI, spinning (and noisy) disks, terminators, chaining all together. A lot of fun, must have been 15+ years since I was doing this on Falcon.

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Re: Falcon IDE read failing at higher frequencies

Post by exxos » Thu Sep 20, 2018 7:47 am

They are exactly that, flukes. Not everyone's machine will over clock the same. Some won't run stable past 20mhz. Some may over clock more.some may work for years at higher speeds then not. Ambient temp is also a factor. Its down to specs of items.

My machine would run stable at 24mhz for hours, the next day it would be unstable as hell. In the end I took nemesis out. Back in the day peoples machines were being killed by it and I didn't want to risk killing my machine. I sure wouldn't fit one again. If I did I'd redesign it to work properly.

Take PC CPUs, some over clock more than others. Such things are overclocking things well over spec, so of course your asking for trouble. A couple ns in the wrong place or a few mv of noise in the wrong place is all it takes.

So yes, it probably was a fluke it just happens to all work before, you may well have damaged something pushing it out of spec than it was before. If its stable at stock the clearly the over clock is causing the issues, its not difficult. Go change a load of random things and you may well get working again. But that's not really solving the problem of borderline bus timings. These things should be fixed by delaying dtack to the CPU, but they never are. I think the design is terrible and needs more work. But hey, I'm the only one who will think that. 20 years of it mostly working properly is good enough for some people.

In any case, its clear you guys think otherwise. I'm sure you will get it going in the end one way or another..
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

mikro
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Re: Falcon IDE read failing at higher frequencies

Post by mikro » Thu Sep 20, 2018 7:52 am

On the contrary Chris, I value your opinion. Just look at it from the user point of view - it worked, user messed something up, now it doesn't. So the explanation "it was never supposed to work" might be true but it doesn't solve the user's problem. :)

It's similar as with the infamous "We don't break users" linux rule -- even if somebody finds a terrible, terrible bug (like an uninitialised pointer), it's forbidden to fix and *and* put a kernel panic error in case of such pointer is detected again. Because what? It used to work and the user doesn't care about unitialised pointers. It worked for him. Not everyone agrees with such policy but it's an interesting way of looking at bugs and design flaws.

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Re: Falcon IDE read failing at higher frequencies

Post by Petari » Thu Sep 20, 2018 9:04 am

It is clear that IDE works not well now, after that shortcut, when it is overclocked. And that before it worked. I don't think that replaced IDEtoSD or SD card, especially the later have some influence in it. Surely they are not all same, some can work faster, some not. It is just that they are new devices, made for much higher speeds that Falcon, overclocked Falcon can.
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