The LaST Upgrade - Part 15 - Bad DMA "fix"

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The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby exxos » Fri Jul 18, 2014 10:53 pm

http://exxos.www.idnet.com/IMPULSE/atari/last/DMAfix/

I had a hour tonight so uploaded the image of the cap mods to the DMA so the mod can be tried on any Atari Machine.

I am not saying this is a "fix all" solution as it is not. Though if you are suffering from random not booting from hard drive, or getting random corruption viewing files in GEM, then its most probable my fix will solve your problems. Of course you need to make sure your PSU is good to start with as that could be the reason the DMA appears to be going faulty, as a side note, the floppy drive will come up random faults too. Using Ecopy, it flags up sectors it cannot format, but those sectors that error are already random. If they were always the same sector then the floppy would be bad. So floppy drive issues can be linked to hard drive issues if the PSU has gone bad.

If people can post what hard drives work and don't work, with what machine and motherboard revision number, and with what number of DMA, then we might be able to get to the bottom of the DMA related issues once and for all. It would help if people could verify their PSU is good as it could otherwise taint the results, A scope to check the 5V ripple is needed.
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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby FujiMan » Sun Jul 20, 2014 4:57 pm

Very cool. :D

I have a 1040Ste4 that has issues booting a Supradrive (which has ICD host adapter + 540mb IBM drive).
I have recapped the PS, so I'll be trying this mod out shortly.

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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby frank.lukas » Sun Jul 20, 2014 6:18 pm

I believe not in this DMA Fix in a STE Machine, so please report back ...
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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby GadgetUK164 » Mon Jul 21, 2014 8:57 pm

I've posted about this before, but thought I would reply again here.

My STFM was not always booting from my UltraSatan - probably 10 to 20% of the time. After adding the caps it now boots every single time. With regards to the STe DMA bug, I am convinced there's was an actual fault in the first batch of chips, so not sure whether there's a work around for that. I know Lotharek did some extensive investigation into those faulty chips and couldn't find a way around the problem. That said, there are other models that suffer from not very well documented design features - like the DMA issue which stopped my STFM booting. Incidentally I've got the exact same revision as the one in the photos on Chris's site.

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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby exxos » Mon Jul 21, 2014 10:30 pm

AFAIK, the general "word" was the -38 would not work in the STE?, which does not hold true in my tests.

If there was a batch of actually faulty -38's when the STE's were made then that could be what jookie saw/had. Though as I have not had a "faulty" STE I can't say if the fix will work or not on the STE. If there is a blown pin on the -38's on the STE, then no, the mod will not solve that. Though other than jookie, I have not seen anyone else saying about actual faulty chip. People just seem to assume its faulty as its a -38 in a STE.

As for the circuit, the STE's DMA is almost identical to the STFM, with exception there are buffers on all the pins, EXCEPT the 2 pins where my caps go. In that respect the STE circuit is identical to the STFM. So any faults on the STFM are most probably on the STE aswell.

My 2 STE's work fine with the -38. AFAIK, people with hard drives have had random issues, not simply "dead" issues, but it is very difficult to obtain users results on it all unless more people get onboard to help with the stuff.

I had one revision STFM board which would work 50% of the time with a -38, but other revisions of board simply would not work at all, I could say in that case the DMA is dead, but the DMA worked perfectly in the STE. So that isn't the problem. The timings on the ST are all running borderline, a 1% tolerance on something is enough for it to either work or not work totally, thats how bad the ST design seems to actually be. Changing to the new DMA is "just" enough to tip it over back into the working state. This does not mean the old DMA is bad. Ironically the -38 could actually be a better chip as it shows up the faults :lol:

For me, fitting a new DMA in a STFM did not work, so the STFM has DMA issues regardless of what DMA chip is used. My mods fix that. Until someone comes along with a "iffy" STE to try the mod on, nobody in the world will ever know if it works or not. I myself simply cannot do anymore work here as I do not have a STE which has a "bad DMA". I have tried about 10 -38s in my STE, no problems at all. I urged people who replace their old suspected duff DMA with the newer one, to send me their old DMA for testing to see if it works in my machine or not. so far nobody has come forward and I posted that request some months ago now.

This is all why I urge people to document motherboard revisions, and try with and without the mod and report back. The mod may work for some STE owners, but not all. It could depend on the hard drive or the PSU, MANY factors. If anyone had a suspected bad STE, they are welcome to send it to me and I will test my Gigafile on it without and without the mod.

GadgetUK has mentioned many times already its solve his STFM problems with US, it solved my problem with GigaFile too. So that is 2 hard drives on the STFM which are now stable after the mod. MORE hard drives NEED testing, and MORE ST/E's.

We can all sit around and debate it for the next 10 years. So unless people get off their rear ends and actually try things out, then everyone suffers with these problems and will continue to do so.
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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby GadgetUK164 » Tue Jul 22, 2014 8:23 am

Totally see where you are coming from! I will look out for one of the -38 DMA chips and have a go with my STe. Can't help but wonder how many chips were binned in the past. I do also wonder if some of the drives themselves have added to the problem.

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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby exxos » Tue Jul 22, 2014 12:44 pm

GadgetUK164 wrote:Totally see where you are coming from! I will look out for one of the -38 DMA chips and have a go with my STe. Can't help but wonder how many chips were binned in the past. I do also wonder if some of the drives themselves have added to the problem.


From what I remember nobody had any issues with the proper Atari drives, it wasn't until 3rd party drives came out that the problems began. I suspect Atari drives used the slower 74xxx logic chips, and later 3rd party drives used 74LSxxx chips. Of course it could also mean Atari used 500ns micros, others 100ns micros. But Its hard to tell unless someone can open up some drives and see whats in there and what chips are used. I suspect its simply a interface speed problem.

Yeah there must be loads of people who have changed the -38 out of a STE because its not been working right, and then changed it and it worked. Though its what's happened to the -38s, probably binned.

Atari must have known there was a problem, I'm sure there was some article by Atari blaming 3rd party drives for not implementing things correctly and that's why 3rd party drives didn't work correctly. Though I think it is just noise on the motherboard, Atari drives using slower logic didn't not care about it, but newer drives using faster logic could respond to noise and cause problems. Though Atari did buffer the DMA on the STE, so clear Atari knew of some problems relating to the DMA. Though I guess they realised the buffering did not solve the problems, so they got some other manufacture to produce the DMA's, still same chip, just different number, and those just happened to work. That's my take on it all :lol:
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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby Dio » Tue Jul 22, 2014 3:38 pm

exxos wrote:From what I remember nobody had any issues with the proper Atari drives, it wasn't until 3rd party drives came out that the problems began. I suspect Atari drives used the slower 74xxx logic chips, and later 3rd party drives used 74LSxxx chips. Of course it could also mean Atari used 500ns micros, others 100ns micros. But Its hard to tell unless someone can open up some drives and see whats in there and what chips are used. I suspect its simply a interface speed problem.

Schematics are out there. On the SH205, ACK is taken off the straight connection between the DB19s via a 62ohm resistor and a diode. This feeds two 74LS chips, and a PAL, with a 5V pullup.

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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby exxos » Tue Jul 22, 2014 5:37 pm

I never thought to look for the Schematics of the Atari drives, though I found it and a quick look, I can see there is a lot of logic going on there. Items like ICD LINK just used a single PAL, so propagation delays throughout would be a lot lower.

On the ST there is a LS inverter, the input "sometimes" triggers the output, if it does, then the DMA faults. The capacitors I add there stop the signal from triggering the LS output, so the DMA behaves. If that LS inverter was a slower TTL type, then the spikes on the input would never trigger a output, but on the LS, it just about can keep up, which is where the problems start. If the signals are passed via 2 LS devices, then chances are input to output simply wouldn't happen, and then no DMA fault.

Maybe somewhere here who has used the ICD link cables or equivalent can shed some light on if they behave on the STFM and STE machines and what DMA chip is being used... I did have a DMA cable, 2 or 3 in fact years ago, but I do not remember ever having any problems with them, but the chip used could have been a slow 500nS or so device anyway. It would be interesting to find out what hard drives out there work and don't work to great, or work on the STE but not STFM.. Even so, I suspect any devices which are faster than LS speeds are likely to have problems.

It would be very hard to draw any solid conclusions without a lot of support from the community as there are so many factors/variables involved. Anyone who has random boot failures or the hard drive not been seen at all (intermittently) , or booted to GEM than showing corrupt file names (intermittently) , should really try this mod and report back if it solves the problems or not, along with what hard drive they are using, motherboard revision number, DMA used.
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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby oehansen » Fri Aug 01, 2014 3:39 pm

What i discovered on my ste, is that it is connected to the timing. This dma chip does not hold the timing that is needed ... I used a pic32 on the other end to experiment with it. If i recall correctly, the papers say 120ns timeout. But reality is closer to fifty.


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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby Guest » Fri Aug 01, 2014 9:47 pm

the problem is reset
just start the hdd train from a floppy copy of hddriver
you can just add no driver to the hdd train
and the floppy copy does it all
the trick is to load the floppy copy with a dam bad dma chip##
as did the owners of the bad dma chips not patched out and ever easily fitted mostly
so use the work around
power all hdd and externals
start the ste or mega ste from a floppy { no issue } then !! use a boot menu app to reload the driver {obviously has a dif name }
and it will all auto boot from then on as long as you dont turn the power off
even cold warm restart then works {rht shft leftsht ctrl alt del} even
and all is well just never turn it off and on
i would also add some value to the capacitor for reset
replace the caps in ataris they are all dried up by now for sure
the flap is over
ignore the bad dma chips crap it means very little
if the floppy copy has the same info on it as the hdd copy does
just then patch your tos rom to remove any delay to floppy or hdd
still think a flip flop double throw on the reset pin of the chip
and two throw power and boot might work
the chip does work after a double reset
hard and soft then hard and soft again ....
where hdd driver just reset as cold and warm at boot
a simple flip flop and a trigger is all thats needed to wake it up once its booted
there is a solution
looking a jookies findings its possible by adding a flipflop and perhaps a latch to hard patch it

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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby SteveBagley » Fri Aug 01, 2014 10:57 pm

exxos wrote:Maybe somewhere here who has used the ICD link cables or equivalent can shed some light on if they behave on the STFM and STE machines and what DMA chip is being used... I did have a DMA cable, 2 or 3 in fact years ago, but I do not remember ever having any problems with them, but the chip used could have been a slow 500nS or so device anyway. It would be interesting to find out what hard drives out there work and don't work to great, or work on the STE but not STFM.. Even so, I suspect any devices which are faster than LS speeds are likely to have problems.


I wrote up (when I was 18!) my experience with the bad DMA chip in my STE for 'Atari Computing' -- that was with a Top-link controller cable (I still have it, and it still works). After an initial issue with a bad Top-link adapter, the STE and drive were fine for probably about a month until it just corrupted the catalog on one partition. I then had the CO25913-38 chip replaced with the C398739 and the system was fine for the next three years. I kept the 25913 for years but I think I binned it in the 2000s with loads of other atari stuff (aka a mistake)…

The articles in ST Format/ST User at the time it first hit (late-90/early-91) certainly suggest the problem also affect Atari drives, and blames the length of the DMA cable (which would alter the capacitance). One thing that's occurred to me as whether we actually know if the C398739 was manufactured for the STE? I notice that the TT also uses the same chip. I wonder if the 25913 didn't work at the faster bus speed of the TT and so they made the C398739 and it also solved the problem in the STE (which would be a very easy fix for Atari since it is pin compatible, existed and required no redesign of the motherboard).

Actually, I also recall a reader's letter in one of 'The ST Club' magazines (either ST Applications or the newsletter) that described a very similar issue with his Mega that was resolved by replacing the motherboard…

Steve

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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby exxos » Sat Aug 02, 2014 9:42 am

I don't know if any other Atari machines used the DMA faster than 8mhz bus ? Length of cable issues is probably why they buffered the DMA on the STE, though they did not buffer the 2 problematic lines. Amazing the fault is still on the STE when its a totally different motherboard and uses different ICs. Though the problem is common on STE and STFM, and its not the DMA which is the common factor, it is something else.

I don't think the DMA is at fault, its the actual implementation and circuit design & layout which is the problem. Replacing the motherboard also makes a difference on the STFM. Its not limited to just the DMA. So its clear there is something else going on. Replacing the DMA isn't a cure, its more of a "cover the problem up" solution.

It really needs a lot more investigation by someone who has LOTS of free time and a lot of motherboards to try out.
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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby Guest » Mon Aug 04, 2014 9:02 pm

its a missing flag on most controllers bridge from 8 overlay to 16 bit

missing masking bit

if you turn off the machine at any point before you turn off the drive

if you have a faulty dma chip you simply turn off the drive then the machine

so the sequence is different

with a good dma turn off the drives anytime
with a bad dma chip turn off the drives before you turn off the machine

its easier with CF sdcards etc

this is the only workaround past load the driver from floppy
turn the machine on turn on the drives then cold boot or use boot floppy
but turn on the machine then after it boots reset THEN turn on the drives
and it will auto boot even

it takes a cold and warm reset to make the drives work with a bad dma chip {two resets init and init chip {with power}}

then it works fine

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Re: The LaST Upgrade - Part 15 - Bad DMA "fix"

Postby Guest » Mon Aug 04, 2014 9:06 pm

i have built a c dma block for pic in picc c and c++ dll in proteus for the dma controller

its a very easy chip to copy

i am making a riser board from dip to prob a pic 32

so any input is helpful but not needed really as it works under stimulus down to 1ns


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