Open source Logic Analyser

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hi all.



I have recently found myself in a position as, I'm sure many of you that
have worked with embedded systems have, where a logic analyser would be of
great advantage to debugging my projects. I have now come up agains a couple
of situations where my CRO just won't cut it.



Unfortunately I am not able to afford a DSD oscilloscope or a commercial
logic analyser. My requirements are much lower then most of the commercial
logic analysers I've come across anyway, I'm looking for something that can
handle a maximum frequency of about 20~40 MHz.



I've decided that I'd like to try and make my own, at the moment I'm
planning a modular architecture based around 74F serries logic and a mcu.
The plan at the moment is to have a control module that is responsible for
interfacing the capture devices to a computer for display. And have up to 8
capture modules (of 8 bits each) that interface to the a 3.3/5V circuit
under test. Also I'd like to try and keep the cost of each module to less
then $100AUD.



I am aware of a design that was published in Elector electronics some months
ago. It was lacking one particular feature that I deem as essential in any
logic analyser. That is the ability to set trigger conditions based on input
conditions, a feature I plan on implementing in my design.



Obviously this design is of a "one-off" nature for myself. I feel that this
is the sort of project that would be of interest to many people involved in
embedded systems at a hobbyist to semi-professional level. So I am
considering a open hardware type approach to this project so that other
people can partake, and I dare say I can learn something from the
experience.



Which brings me to the point of this post. Does anyone know of a good
sourceforge type site for open hardware development.  I was aware of
openh.org but they seem to have disappeared off the face of the internet.
Also I was hopping to gauge the level of interest in people, would anybody
in this newsgroup be likely to use such a product if it was developed.



Regards



Craig Rodgers




Re: Open source Logic Analyser
Craig ,

This isn't really an answer to your question about open-source hardware,
rather an idea of a way to get your logic analyzer.

Consider using an FPGA.

Altera Cyclone is an excellent part for this:

The EP1C6Q240 has :

4 dedicated clock lines for sampling
Loads of IO
4 IO banks, each of which can operate from different voltage levels
Embedded memory arrays for waveform storage
Lots of embedded logic / latches to create complex multi-state triggers
Free development software

One thing that might be a pain is that it isn't directly 5v tolerant, but a
few 5v tolerant low voltage buffers isn't much of an overhead.

Gary.


Quoted text here. Click to load it
couple
can
8
months
input
this
in



Re: Open source Logic Analyser
I had actually given the idea of an FPGA based design some thought. I would
love to be able to be let loose on an FPGA, I think I've got enough VHDL &
Verilog under my belt to give it a decent go.

But getting access to the synthesis tools always seems to cause issues. The
"free" ones from the manufacture always seem overly crippled.

Also, this one seems to be something that I've missed along the way, how the
F**k do you program the buggers once you've synthesized your design. I think
that the old school PLD's from Xilinx etc used to require an external EPROM
to store the binary mask in. I think the manufactures finally started
providing Flash based ones but I've got no idea how you'd go about actually
downloading the mask to one with out requiring some expensive programmer.

FPGA's at the moment seem too expensive, the per component cost is high, the
cost of development tools is large. And the price of the development boards
I've seen is some what excessive.

If I do this project I'd like to do it in such away that it affordable and
accessible for almost everyone. I think that means I'm going to have to
accept some loss of flexibility and stick to readily available components. I
feel that 74F series components are probable the most widely available set
of components suitable for the job. May be I'm wrong I'd love to hear
suggestions, particularly those regarding free/low cost FPGA development
tools

Craig



Quoted text here. Click to load it
a
of
commercial
mcu.
for
to
less
any
internet.
anybody



Re: Open source Logic Analyser
Atmel still has external eeprom type-fpgas I think. I have a few I never
used.

Quoted text here. Click to load it
would
The
the
think
EPROM
actually
the
boards
I
but
in
that
be
commercial
that
circuit
involved
other



Re: Open source Logic Analyser
Altera's web edition of Quartus II software is free, and is pretty much full
featured - the limitations are in devices supported (i.e not their screaming
high end Stratix devices) and there are no third party synthesis/simulation
tools bundled (Altera's native ones seem fine to me)

The EP1C6Q240 is around USD 24 in development quantities, and Altera have a
low cost serial FLASH configuration device (don't know what low cost means
in practice) that can be JTAG ISP'ed using a cheap ByteBlaster parallel
cable.

I don't know about evaluation boards and device programmers - Altera's
website lists Cyclone development kits down to USD 500.

I hadn't used an FPGA for 10 years, but I just completed a design with the
above part and it was a breeze.

Quoted text here. Click to load it
would
The
the
think
EPROM
actually
the
boards
I
but
in
that
be
commercial
that
circuit
involved
other



Re: Open source Logic Analyser
On Fri, 27 Jun 2003 14:29:31 +1000, "Craig Rodgers"

Quoted text here. Click to load it

Hi Craig,
While it is possible to do a logic analyser with 74F/AC series logic,
it's a logistic nightmare, and no one will be interested in building
it, even if it's got supposedly "easy to get" 74 logic.
Trying to do fully maskable triggering, with 8 bit busses running
everywhere, skew, timing, buffering, storage/retrieval, latching, all
across dozens of channels is a big pain in the ass from a PCB
perspective. You'd be talking dense 4 layers boards, and the cost of
those would more than offset the cost of going the PLD/FPGA solution.
It would also be physically BIG, and if you were to go to a modular 8
channels per card approach, you'd have to sort out motherboard
mounting, bus interfaces and many other issues. It's ugly, don't do
it, you'll regret it.

Many of the FPGA/PLD vendors have free tools available, even if they
are limited. Lattice and Atmel also have suitable FPGA/PLD solutions.
If you have to pay much for software/hardware to do FPGA/PLD then you
are going about it the wrong way. Flash devices are serial JTAG
download, and you can often build your own serial cable from info
available on the net. Same for the other FPGA, but they serial
download into an external Flash or EEPROM device.
A logic analyser is not complex, so you don't ned anything super
fancy, a low level PLD will suffice, perhaps even one per 8 or 16
channels. That way you can stick to easy to use packages. External
SRAM is cheap and easy, use cache RAM from old PC's, they can be had
for FREE!. Using SRAM in an FPGA might seem neat, but it pushes up you
FPGA complexity curve and you are looking at big QFP or BGA packages -
yuk. Once again, not many enthusists are going to touch that, in fact
I'd be willing to say none.

The biggest issue with logic analysers though is probing, as others
have mentioned. It's complex, and there is no easy solution to it.
It's a major reason why DIY logic analysers are not, and never will be
popular.

Regards
Dave :)
---------------------------
(remove the "_" from my email address to reply)

Re: Open source Logic Analyser
Circuit Cellar INK, Issue 89, Dec. 97
"A Simple Multipurpose Logic Analyser"
by Janusz Mlodzianowski
http://panda.bg.univ.gda.pl/~janusz /

Might be a useful reference.




Re: Open source Logic Analyser
http://panda.bg.univ.gda.pl/~janusz/software.html#anlog

"The analyser consists of up to 40 TTL channels, connects to a host PC via
parallel printer port and is capable of capturing data at a frequency of up
to 50 MHz (external, and 16 internal frequencies). The trigger word can be
set to any combination of "Low", "High" and "Don't care" states. In
addition, a preset number of Triggers and samples after the final Trigger
can be specified. The Logic Analyser buffer is 2048 samples wide."



Re: Open source Logic Analyser
Except no documentation...

Quoted text here. Click to load it
up



Re: Open source Logic Analyser
Quoted text here. Click to load it

Logic analysis is one of my favorite rant topics, so buckle up.
What do you mean by 20-40 MHz?  If you mean state analysis of a system
that has states that can change every 25 ns, you have one set of
problems.  If you mean you want to look for timing problems on a system
that changes state every 25 ns, you have a different set of problems.

If you want to do it with affordable hardware, ie hardware that's only a
few times faster performance to what you're debugging, plan on
pipelining your word recognizer.

A LOGIC ANALYZER IS USELESS IF YOU CAN'T TRUST IT COMPLETELY!!

Channel skew will drive you buggy.  You wanna build 64 channels spread
across 8 cables and keep the skew low.  Getting the signal from the
source without loading it and with well defined notions of 1 and 0 and
without adding skew and crosstalk and, and, and is a VERY difficult
problem.  This was 20 years ago at Tektronix, we got to
10 MHz, just barely, by using ribbon cable with a ground plane along the
whole length.  The higher speed stuff used lots of twisted pairs in a
round cable.  Remember that typical cable is made by running one wire
down the center and twisting the others around it.  This is DISASTER
for a logic analyzer.  You need special cables.

There's an interesting technique that revolves around a FPGA.  You
compile the trigger recognizer state machine on the spot and download
it to the FPGA.  Years ago, when I approached FPGA vendors about the
subject, they flatly refused to disclose how to program their parts.
More recently, there's a commercial analyzer on the market that appears
to work just that way.  Don't remember the name, but they sell 'em at Fry's.

I built a probe hooked to a socket, programmed a GAL20V8 as a word
recognizer and used that to trigger my scope or simple LA that had
insufficient trigger capability.  Was a pain to program each time, but
I was able to do things I couldn't do otherwise.

I've found that most problems where you're in control of the design fit
into two categories.
1) you can make indirect measurements and determine the source of the
problem logically.
2) It's very complex and intermittent and even the best LA won't help
you. ie debugging the innards of a CPU.

Yep, there are situations in between where a good LA will help, but as a
percentage, it ain't much.

And there's always that ole chicken-egg problem.  It takes a logic
analyzer to debug a logic analyzer design.

I could go on for days, but I'm tired.

Bottom line:
If your time has any value, go buy a used logic analyzer.  Make sure it
comes with probes.

If you're just in it to build one and don't really care if you can trust
it, go right ahead and have fun with it.  Start with the biggest FPGA
that you can afford the tools to program.  Choose your glue logic family
from those who's 0 and 1 propagation delays are the same.

mike

--
Bunch of stuff For Sale and Wanted at the link below.
21' RV, 400cc Dirt Bike
We've slightly trimmed the long signature. Click to see the full one.
Re: Open source Logic Analyser
Quoted text here. Click to load it

More analysis of a system that can change states upto each 50ns or so.
I realise that in reality I'm dreaming if i think i can pick up glitches a
magnitude smaller in a system at this speed using off the self components.

Quoted text here. Click to load it

agrred, and so long as you realise the limitations of your equipment I feel
you should be able to trust it.

Quoted text here. Click to load it

Thank you this is an area I hadn't thought about. Clearly I'm going to have
to give it some more thought particuarly channel skew. Although I was under
the impression that most of the twisted pair cables aroung today were of a
resonable quality. Surely if I can transmit Gbs down CAT 5 even taking into
account the pulse shaping to help limint the ISI then it's not unreasonable
to
think i can recieve 20MHz signals down a similar twisted pair with minimal
cross talk problems..

Quoted text here. Click to load it
Fry's.

May be a suitable alternative for me at the moment.

Quoted text here. Click to load it

I don't expect a logic analyser to be a magic bullet in any circumstances.
I do expect to get some time savings from it from not having to repeat
the fault condition every 2 minuets in order to take another reading.


Quoted text here. Click to load it

if I could i would.

Quoted text here. Click to load it

Thanks for the tip.

Craig



Re: Open source Logic Analyser
Hi!

Quoted text here. Click to load it

Thanks for the description. You surely pointed out a number of problems. How
about this approach: put all the high-freq part of the LA into an FPGA, put
a small uC/DSP by side of it, fix the whole thing up with a USB/Ethernet
port and stuff the whole thing into the box of the POD of a usual LA. The
cable length would be < 10cm (4 inches) in that case, the channel number
whould be 8-9, but definitely under 16. More of these could be connected to
a PC and be grouped into a wider virtual analizer. Triggering over multiple
PODs like this would be hard though...

Regards,
Andras Tantos

Re: Open source Logic Analyser
Quoted text here. Click to load it
<snip>
Quoted text here. Click to load it

 That's a good idea - very low cost :)
 - these days, you'd use CPLD like Atmels ATF150x family.
ISP progamming, low power, and 5V capable.
 Tools are free on the web.

 Logic Analysers are just dual-port memory load/read, once you
have the trigger qualified.

 -jg

Re: Open source Logic Analyser

Quoted text here. Click to load it
couple
can
8
months
input
this
in

look under projects on avrfreaks.

also you will find a few searching on google.

for a logic analyser have a look at www.rockylogic.com.
I have an ant8. Works very well for circuits under 100MHz.

for fpga.
may want to have a look at actel. have a flash based fpga so you
don't need a eeprom or data flash to store
your bitstram in.

also have a look on opencores.org

Alex



Re: Open source Logic Analyser

Quoted text here. Click to load it
of
commercial
entries,
that

no much help in your not in the US.
Note the op's email address   .au  = Australia.



Re: Open source Logic Analyser
Quoted text here. Click to load it

So what? Look at my e-mail address ( .ch ) which means Switzerland. I
bought 3 scopes and 4 analyzers for me and others from e-bay.com (i.e.
from the US). Ok, I had ot add ~$120 shipping but considering the fact
that you then get working systems which you can trust and that you are
not faced with X hours of developement time trouble etc. etc. made it
very worthwile. I haven't regretted yet a single purchase yet. Ok, if
the original poster does this for the fun of it and for learing
without pressure of having an analyzer to complete a task etc.
building his own might be the right decission - otherwise e-bay is
really a good option.

Just my 2 though

Markus

Re: Open source Logic Analyser

Quoted text here. Click to load it

Agreed. I've bought several items of test gear from the US via Ebay in
the last year or so, including a 1630G logic analyser (don't laugh :-)
with all probes and manual for ~$200. Not the latest and greatest, but
more than adequate for the micro and comms stuff i'm doing at the mo.
Looks like it had never been used internally. Shipping was around $80,
surface and took about 4-5 weeks. Ebay is the first place I look for
test gear now and with the $ at an all time low, some of the kit is a
real steal, even with the shipping and import duty.

Unless you have a real interest and pressing desire to build your own,
would recommend you buy, as you can't build one of the same quality for
the price and man hours...

Chris

Re: Open source Logic Analyser
On Fri, 27 Jun 2003 13:31:27 +1000, "Craig Rodgers"
Quoted text here. Click to load it

Hi Craig,
You may be interested in my old design that was published in
Electronics Australia many years back:
http://electronics.alternatezone.com/pcla.htm

Seriously, forget 74F series logic and go for a PLD/FPGA based design.
Interface to the PC via USB.
This has already been done here with the ANT-8, but it's not open
source:
http://www.usb-instruments.com/hardware-ANT8.htm
Bit expensive at over $300AU though.

Regards
Dave :)
---------------------------
(remove the "_" from my email address to reply)

Re: Open source Logic Analyser
Quoted text here. Click to load it

Check out Bitscope.

http://www.bitscope.com /

--

Regards
David Milne

Re: Open source Logic Analyser
Well I've been convinced. I think that a PLD based approach is probably a
reasonable one to take. The cost of the FPGA's themselves seem to have
dropped significantly since I last checked them. I'm off to start comparing
the synthesis tools from a few different vendors.





Quoted text here. Click to load it
couple
can
8
months
input
this
in



Site Timeline