Re: PCI Bus, ongoing

From: Keith Williams (krw_at_att.bizzzz)
Date: 08/25/04 

Date: Wed, 25 Aug 2004 14:52:12 -0400

In article <412cb74a$2$woehfu$mr2ice@giganews.aros.net>,
mountains@iname.com says...
> >> things. First thing I did was download the PCI configuration using one of the
> >> utilities that was pointed out by someone here.
>
> Guess it wouldn't hurt to state the obvious, that I got the configuration
> while using a PC that gets along with the PCI card in question :-)

Gee, the failing configuration would get you much more information! ;-)

> >All Via chipsets? Via has had problems here. There wouldn't be any Creative
> >Labs (SoundBlaster &such) cards in these systems? They're well known to be
> >problematic. Though they should at least POST.
>
> I make sure there are no other cards in the board, except for the AGP video.
> It works on one PC with a VIA chipset, but not another......

Different brands? Different models? Same brand/model?

> I am limited to
> how many PCs are laying around. Certainly not as many to choose from as the
> entire customer base. I am unable to find any consistencies with chip sets
> among those I have to work with.

Can you get feedback from customers with failing units so you can do a
correlation?

> >Unlikely. The PCI standard hasn't changed in years. It could be a crappy
> >chipset implementation though.
>
> I am narrowing it down to either crappy MB designs, or crappy PCI card
> layout...... :-)

Ouch.

> Seems the PLX device is PCI 2.1 compliant, and so are the MBs I am using.

That's what they claim, anyway. PCI 2.1 has been around for years, so
I'm doubting that it has any thing to do with the spec.
 
> >> The failure is a total lockup of the machine on powerup. No boot,
> >> nothing. No beeps from the BIOS. All I get is the fan coming on :) The
> >> video never inits, as the monitor power light stays on amber.
>
> >Are you *sure* the card mechanicals are correct and nothing is getting
> >shorted out? There *is* a reset on the PCI channel? If you'renot getting
> >any beeps it's likely not even fetching POST code from memory, which coudl
> >happen if the card is shorting out the PCUI channel (BIOS is often handing
> >off the southbridge on the ISA side of the PCI/ISA bridge.
>
> I have gone over the board, and am sure in the sense that the same card works
> in every other PC around here, except for one other, that seems to share no
> common characteristics.
>
> I don't think it is a short issue, but I am pretty convinced the card is
> absolutely hanging the bus, as there are no beeps, and no disk activity at
> all.
>
> >You might see if
> >you canborrow a POST card to see how far it goes.
>
> Oooohhhh, good idea. I have no idea where to borrow one :-) but its something
> to check out and try.

I'm fairly certain I've seen 'em cheap in catalogs. I just did a quick
search and only found them in the low-mid $hundreds though. Maybe you
could rent a PCI bus analyzer for a month? Dunno what your financial
commitments are...

As an aside, I thought it interesting that my motherboard had a POST
display integrated in. Nice touch, but Murphy would dictate that any
with this nice feature would always work. ;-)

> >> I then did the purely scientific test of putting some tape over a group
> >> of pins to remove them from the bus, and the PC booted up fine. I tried
> >> narrowing it down, in hopes of getting a clue, but as some of you will
> >> guess, it is basically just a matter of covering any of the address/data
> >> lines and the PC will boot. I got it all the way down to just one
> >> address line and it still allowed the PC to boot, but of course, the
> >> card did not appear in any configuration, or in the software that
> >> controls the card itself.
>
> >Good deductions. Which address pin? You might have a short there.
>
> Any address pin..... any one at all, which indicates??

...that my brain hurts? Masking any *single* AD pin allows it to boot?
I gotta think on that one.

> >> I am attempting to contact PLX and get an application engineer to give
> >> me a hand, but I am hoping there might be some ideas here to move this
> >> along if I can. It seems that the PLX chip is certainly not
> >> initializing, and of course, and its hanging the bus.
>
> >If it didn't initialize it should *not* be hanging the bus.
>
> I agree.

There's an idea. Perhaps you can force a reset on the PLX chip. Maybe
change from fast to slow boot (more memory testing) in BIOS. I'm
thinking that there may be a boot timing issue and the PCI controller
and card are dueling (a long shot).
>
> >I *doubt* that it's the problem, but the clock line should *not* be short
> >(the spec calls for 2.5" +/- .1"). Indeed to meet spec it should be a
> >serpentine around the bottom of the card.
>
> The clock line is 1.2" Could be a mixup there I guess. I am not so proud as
> to confess to such errors :-) but it works unfailingly in so many machines,
> for so many years, I am having a hard time accepting that as an issue.

The spec is there for a reason. The board maker may be assuming you're
following the spec. That said, my first PCI board had the exact same
Ah $#!+ as yours (there was a reason I pulled this spec out of my
@$$ ;). Though, I got lucky and it worked. I had the added advantage
that it only had to work in a small number of systems (exactly one ;-).
Were it a product, I'd have been more worried.

> I can
> go along with crappy MB design making the problem appear. The MB in front of
> me is an ASUS P5, not exactly new, and not really a poor MB, IMO.

The P5 is failing? Ohhh! I found that ASUS products of this era were
usually very good. I used to "reverse-engineer" such boards for
comparability testing.

> Care to venture a guess as to the idea of cutting the clock line and using
> jumper wire to prove a point?

Do you have inner planes on your board (I thought there was an issue
here). Without the planes getting the timing down pat would be a
problem. I'm not giving it a high percentage of success, but it's
worth a try, if you have to guess (insufficient test equipment
available).

> >> Anyone use the PLX chip before who knows a bit about it, or a similar
> >> device?
>
>
> >Aw, coem on! Hardware is where the fun is! Crap on C/C++. ;-)
>
> :-) I was in it up to my neck for over a dozen years. Stuff happened in life,
> layoffs, and I ended up as a PCB designer (not that this board is my best work
> <g>) and then got canned from that almost three years ago after the WTC fell.
> Haven't been able to find full time work since, so I have been doing other
> stuff. Programming is not in my blood. I would prefer a full time hardware gig
> again, but circumstances have conspired against me. Seems that unless one can
> do hardware and write code, the opportunities are quite limited. For the first
> 18 months after the attacks, there were no jobs, and being out that long
> doesn't impress HR folks......I live in Utah, and at one time, there was lots
> of work. Now, its mostly moving overseas and to the south. Few positions, lots
> of people looking.

Definitely not good. I managed to make it through (in a few cases I
really don't know how). My project was canceled, no assignment for five
months when the layoffs came. The programmer I was working with was
laid off and the boss told me to "go see the verification folks; they
need help". To which I answered; "I can do that". ;-)

I just turned the 30-year corner a few months ago (retirement locked in
and all that good stuff :-). I've looked around out in the wild and
there are hardware jobs, but one has to be ready to move to them. I'd
really like to do more such hardware design, but the paycheck shows up
on time and I think again.

> Anyway, gotta get this done first. I am loathe to have to tell this small
> business that the layout "might" be an issue, and redo it unless I can
> convince myself the cash outlay for them will be a good investment. If you
> have worked with the PLX, you know that its not a real simple layout from
> that big 160 pin PLCC to PCI pins in the first place. Internal planes would be
> good, but cost is a real concern for them.

The PLX chip was easy. It laid itself out (fan-out was perfect for two
layers - no crossings). The FGA680 and BGA256 FPGAs, and the BGA
processor were somewhat more of a challenge. ;-)

> Thanks a lot for the ideas and conversation.

Good luck! ...and do tell us what you find. It's good to keep a bag-
o-tricks up one's sleeve. 

-- 
  Keith

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