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'[PIC]: I2C sniffer'
2002\05\16@102606 by Lawrence Lile

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On an analog scope, a burst of I2C data looks like a stream of bullets.
After beating my head against the lab bench during the last encounter with
I2C, I've concluded that one needs an I2C sniffer to really troubleshoot one
of these systems.  (Unless of course one has a $10,000 scope ;-)  This would
be a passive beast that would sit on the I2C bus and report when it sees a
start bit, address, ACK or data, and also report which is which.  I could
imagine sending the info out over an RS232 line, and also displaying it on a
4-line LCD, since a lot of conversations on an I2C bus might be pretty
short.  Didn't find any such animal in the PIClist archives.  Has anybody
looked  into this?


-- Lawrence Lile
Sr. Project Engineer
Salton inc. Toastmaster Div.
573-446-5661 Voice
573-446-5676 Fax

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2002\05\16@104910 by Trevor Page

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Lawrence,

I was recently asked to build an I2C monitor.

My first approach was to use the Philps PCF8584 I2C / parallel interface
chip. This IC has a special monitor mode, which is very convenient if you
wish to implement a basic 100KHz bus monitor. Wire it up to a 16F877 or
something to send the data via RS232, and there you go. It's not the best
monitor in the world - personally there are a few things I don't like the
8584 chip. For instance, IIRC the 8584's interrupts cannot be used when in
monitor mode, which is plain stupid (I could be wrong on that detail, but I
remember it was something like that). I think you end up having to waste
lots of processor time polling a bit instead to check on activity...
something like that. I think this is all to do with the fact that the
monitor mode was really an afterthought on the 8584.

The 8584 is rated for bus speeds up to 100KHz but a friend of mine has
claimed that his PCF8584-based monitor circuit worked perfectly well on a
400KHz bus.

I also implemented a monitor using just a fast AVR, with some external logic
(flipflops + inverters) to detect start / stop conditions. I used a USBMOD2
USB interface to pipe the data to the PC. My intention was to produce a
better 400KHz monitor without using the PCF8584 - but this was surprisingly
difficult to do using a mid-range AVR. Given the chance, I'd probably do it
again using a Ubicom (Scenix) processor, or with a CPLD or something. In
fact the reason I tried the AVR approach and ditched the 8584 was because I
never believed it would work reliably at 400KHz since the datasheet clearly
states that it goes 100KHz tops - I was gutted when my friend proved me
wrong, but there you go ;o)

I reckon the easiest approach might be to take a PCF8584 and maybe wire it's
parallel interface directly to your PCs parallel port, and write a nice
Windows monitor application? Erm.. maybe that's what I should have done :)

Regards

Trevor.




> {Original Message removed}

2002\05\16@110341 by Alan B. Pearce

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>On an analog scope, a burst of I2C data looks
>like a stream of bullets. After beating my head
>against the lab bench during the last encounter
>with I2C, I've concluded that one needs an I2C
>sniffer to really troubleshoot one of these systems.
>(Unless of course one has a $10,000 scope ;-)

Well I am hoping that my TDS2024 will do this for me. I suspect that pretty
well any DSO would be suitable, the biggest problem being the length of
message you could look at.


>This would be a passive beast that would sit on the
>I2C bus and report when it sees a start bit, address,
>ACK or data, and also report which is which.  I could
>imagine sending the info out over an RS232 line, and
>also displaying it on a 4-line LCD, since a lot of
>conversations on an I2C bus might be pretty short.
>Didn't find any such animal in the PIClist archives.
>Has anybody looked into this?

An ordinary PIC with I2C hardware cannot do this as it requires to match the
I2C address to something you program inside. It could be done with a Pic
otherwise (with limitations) if you only monitored one address. You could do
it by rehashing a software I2C implementation so it did not look for an
address.

However Philips have been smart in this area, and one of their parallel
interface chips can be put into a monitor mode and monitor all I2C traffic.
Check out the PCF8584 chip. Hooked to a PIC should do what you want. If you
want to go straight to a PC then Elector Magazine did an I2C analyser using
this chip hooked to a printer port. I would have to look out the issue
number if you want it.

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2002\05\16@110752 by Lawrence Lile

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I'll look into the 8584 when I get more serious about this project.  An I2C
sniffer is definitely one of the tools I need to have in my bag of tricks,
as important as an RS232 breakout box was in the '80's.   Does anybody make
a commercial one?

--Lawrence
----- Original Message -----
From: "Trevor Page" <trevor.pagespamKILLspamPACE.CO.UK>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Thursday, May 16, 2002 9:46 AM
Subject: Re: [PIC]: I2C sniffer


{Quote hidden}

logic
> (flipflops + inverters) to detect start / stop conditions. I used a
USBMOD2
> USB interface to pipe the data to the PC. My intention was to produce a
> better 400KHz monitor without using the PCF8584 - but this was
surprisingly
> difficult to do using a mid-range AVR. Given the chance, I'd probably do
it
> again using a Ubicom (Scenix) processor, or with a CPLD or something. In
> fact the reason I tried the AVR approach and ditched the 8584 was because
I
> never believed it would work reliably at 400KHz since the datasheet
clearly
> states that it goes 100KHz tops - I was gutted when my friend proved me
> wrong, but there you go ;o)
>
> I reckon the easiest approach might be to take a PCF8584 and maybe wire
it's
> parallel interface directly to your PCs parallel port, and write a nice
> Windows monitor application? Erm.. maybe that's what I should have done :)
>
> Regards
>
> Trevor.
>
>
>
>
> > {Original Message removed}

2002\05\16@113436 by Alan B. Pearce

face picon face
>Does anybody make a commercial one?

again Philips seem to have something under the model number OM1022, which
looks like it is a board you use with a PC and comes with software as well.
Sounds like it is an 8584 :)

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2002\05\16@121206 by Alan B. Pearce

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www.avsc.nl/i2c_chapc.htm

Check this for some possible pointers to I2C development tools. have not
checked to see if they are still valid. May require some searching, but
there are some free development tools quoted.

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2002\05\16@121900 by Alan B. Pearce

face picon face
www.mcc-us.com/pr20010100.htm

Ya might also like to check this one out for a commercial device. Must be
getting closer to your neck of the woods than I am :)

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2002\05\16@123939 by Mike Mansheim

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> I'll look into the 8584 when I get more serious about this project.  An
> I2C sniffer is definitely one of the tools I need to have in my bag of
> tricks, as important as an RS232 breakout box was in the '80's.   Does
> anybody make a commercial one?

Probably pricy, but Micro Computer Control makes commercial i2c stuff,
including bus monitors.    http://www.mcc-us.com/
Don't know what your scope budget is, but our HP (Agilent) 54622 works
VERY nicely for i2c work.  It can trigger on i2c stuff, including
address, but more importantly, the so-called "deep memory" on this scope
lets you capture a ton of data, which can still be expanded and examined
one pulse at a time.
I prefer the scope over a bus monitor, especially if you are brewing your
own i2c code.  There's no substitute for looking at the pulse train, vs.
what a monitor thinks that pulse train means.

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2002\05\16@124431 by Richard Crossley

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> -----Original Message-----
> From: pic microcontroller discussion list
> [RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU] On Behalf Of Alan B. Pearce
> Sent: 16 May 2002 16:03
> To: spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU
> Subject: Re: [PIC]: I2C sniffer
>
>
> >On an analog scope, a burst of I2C data looks
> >like a stream of bullets. After beating my head
> >against the lab bench during the last encounter
> >with I2C, I've concluded that one needs an I2C
> >sniffer to really troubleshoot one of these systems.
> >(Unless of course one has a $10,000 scope ;-)
>
> Well I am hoping that my TDS2024 will do this for me. I
> suspect that pretty well any DSO would be suitable, the
> biggest problem being the length of message you could look at.

I was a able to see enough with a 100KHz bus using the TDS2024.
As you say finding the right part of the message is a pain, do expect to
spend hours fiddling with the trigger delay, I was dealing with packets
varying in size from 6 to 53 bytes and all the PICs were handling timer
and external interrupts in addition, and using SCL clock stretching so I
had to put 'marker bytes' into the packets in debug mode to find out
just where I was in the stream.
My system has up to 30 18C452s all running, completely asynchronously,
as both multi-master and slave. The 'really fun' parts were tracking
down both faults in the arbitration logic and my own DHCP like address
allocation system (all devices boot with identical I2C address and
discover their peers).
Small value resistors inline with each device's SDA/SCL were invaluable
in detecting just which device was pulling the bus low.

Richard.

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2002\05\16@130531 by Peter L. Peres

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There is a I2C/Rs232 converter someone is selling. I think it is
PIC-based. Of course you can build your own. Since usually the reason to
troubleshoot I2C is incorrect timing or signal levels a DSO is the way to
go. A cheap one that does 1MHz and 2 channels (Game Boy ?) should do it.

Peter

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2002\05\16@132417 by Herbert Graf

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I actually built a PC based logic analyzer that worked out really well for
debugging I2C problems, I'm planning on posting it, eventually but any of
the cheap PC based logic analyzers out there with a sample rate above about
2MHz will work fine for any I2C situation. TTYL

> {Original Message removed}

2002\05\16@161125 by Micro Eng

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Just bought an I2C serial interface....$200 I think...



{Quote hidden}

> > {Original Message removed}

2002\05\16@161134 by Micro Eng

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also....

http://www.mcc-us.com


{Quote hidden}

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2002\05\16@162742 by Micro Eng

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Thats the unit I have....works pretty good

>From: "Alan B. Pearce" <spamBeGoneA.B.PearceSTOPspamspamEraseMERL.AC.UK>
>Reply-To: pic microcontroller discussion list <KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU>
>To: EraseMEPICLISTspamEraseMEMITVMA.MIT.EDU
>Subject: Re: [PIC]: I2C sniffer
>Date: Thu, 16 May 2002 17:18:03 +0100
>
>http://www.mcc-us.com/pr20010100.htm
>
>Ya might also like to check this one out for a commercial device. Must be
>getting closer to your neck of the woods than I am :)
>
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>


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