Advice on Logic Analyzer

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Hi

I'm considering to purchase a pc based logic analyzer. After a bit of
shopping around I narrowed down my options to either the Logicport
from Intronix or the Annie-USB from Janatek, maybe even their Logic-16
as well.

Before I make the final decision, is there anyone of you that owns any
of these instruments?
The obvious reason for the logicport is the fact that it costs only U
$389 for 32 channels and 500Mhz sampling rate. I have however read
this little faq article on janatek's website on how to
evaluate(compare) between various logic analyzers and I'm having
doubts of buying a logicport. The Annie-USB although a tad more
expensive seems to be a really good quality instrument. Any of you
having thoughts on this.

Luckily the need is not pressing so I have a couple of days.

Re: Advice on Logic Analyzer
On Mon, 14 Apr 2008 06:31:32 -0700 (PDT), logicgeek

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I've never used a logic analyzer. A dual-trace digital scope and a
little thinking is usually enough.

John


Re: Advice on Logic Analyzer



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Strongly agree. "Little thinking" is the key part.
BTW, I've never had any use of ICE for the same reason.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Re: Advice on Logic Analyzer
On Mon, 14 Apr 2008 09:08:35 -0500, Vladimir Vassilevsky

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I do use a hex background debugger (the PEMicro pod, for the 68332)
when testing embedded code. It lets me load code into RAM (which will
later be eprom), run it, step it, breakpoint, patch, snoop registers
and ram. It also lets me directly thrash hardware interfaces. A
combination of untested digital+analog hardware, untested FPGAs, and
4-12 kilobytes of untested uP code, running on a brand-new pc board,
exceeds *my* ability to just think it through.

The bdm pod plugs into a little 10-pin header that we include on all
of our embedded products.

John


Re: Advice on Logic Analyzer



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I usually don't make many mistakes of the sort that can be helped by an
ICE. The ICE can be handy for troubleshooting of the minor technical
problems... but the best cure is not to create those problems at first time.

Initially, I develop the flashloader with the basic diagnostic facility
and the minimum hardware drivers for a new board. From there, the real
development starts. I can output whatever parameters I need through
whatever interface I have (Ethernet/CAN/RS232), without interferring
with the real time flow of the program and the states of cache and SDRAM.

I could never understand why some people need to look at the
SPI/I2C/UART/CAN lines when it is well known that the interface outputs
exactly what you are writing into it and exactly in the way you
configured it. The upper level protocol progress is better seen from the
inside of the machine rather then by observing the lines.

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I have to include the 14-pin JTAG connector, too, because some other
developers just can't live without it :)


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com


Re: Advice on Logic Analyzer
On Mon, 14 Apr 2008 08:19:02 -0700, John Larkin

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Do you use JTAG as well?

Re: Advice on Logic Analyzer

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Not so far. The Freescale BDM is sorta jtag, but not exactly. The
Xilinx FPGAs have a jtag port, but we don't use it: we program them in
slave serial mode, essentially SPI.

John


Re: Advice on Logic Analyzer
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Actually, there are bugs in some UARTs and similar bits of microcontroller
hardware.  Additionally, just because your code is good doesn't mean the code
or hardware you're talking to is -- I've seen plenty of examples of bit-banged
I2C code that violated the spec, and since usually the person who wrote the
code isn't aware of the fact (or didn't bother to document it even if they
did), the only way you'll find out exactly what's wrong is usually to probe
the actual data lines.

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Yes, once the lowest level interface is "trustworthy," I agree.




Re: Advice on Logic Analyzer
On Mon, 14 Apr 2008 17:57:59 -0500, Vladimir Vassilevsky

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It can be a real help when, e.g., bringing up CAN on a new (to me)
microcontroller family for the first time. CAN peripherals have
wonderful "smarts" but getting there means a different register set
for every manufacturer.

--
Rich Webb     Norfolk, VA

Re: Advice on Logic Analyzer
On Mon, 14 Apr 2008 07:01:47 -0700, John Larkin

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But hand-decoding an SPI data stream can get a little tiring. As the
saying goes: been there, done that, skipped a bit - had to start over.

The OP might also want to look at the Ant8 and Ant18 analyzers from
Rocky Logic http://www.rockylogic.com

That said, I've been using one of the Intronix LogicPorts for years.
Got it hooked up now watching a couple of CAN data streams, a 1 PPS
time mark, a UART's TX & RX, and a half-dozen discrete I/O pins. Their
latest firmware spin added the CAN interpreter to the existing SPI,
I2C, and async serial interpreters. Makes it very easy to check a
NMEA-to-CAN gateway.

--
Rich Webb     Norfolk, VA

Re: Advice on Logic Analyzer
On Mon, 14 Apr 2008 11:57:33 -0400, Rich Webb

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Scopes can do that these days, though some require extra $ to unlock
the feature in firmware.

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Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: Advice on Logic Analyzer
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You might just get a chance if you end up rolling your own PCI interface and
having to debug it. :-)




Re: Advice on Logic Analyzer
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Why would you do that in 2008?

Re: Advice on Logic Analyzer
On Mon, 14 Apr 2008 11:21:21 -0700 (PDT), snipped-for-privacy@netzero.com

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Amen, brother.

John


Re: Advice on Logic Analyzer
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There was a separate thread where he was discussing various ways of
interfacing to the PCI bus and doing anything from rolling your own interface
from scratch to using the simple/free PCI interfaces inside an FPGA to using a
full-fledged interface (still in an FPGA) to using the, e.g., PLX interface
ICs that do it all for you... hence I was just making the point that someone
who did choose to go the "roll your own" route would probably end up using a
logic analyzer, sooner or later, even though realistically I doubt John is
going to go that route and agree with you that, these days, very few people
could make a good case for doing so anyway.

Somewhat similar to spectrum analyzers these days where the basic performance
isn't really that much better than those of a decade past but where you're
paying to get a decoded trace of, e.g., a CDMA or WiMax RF sequence, a lot of
the "value add" in a logic analyzer is now in the decoding provided as well.
Even something as "simple" as USB is pretty difficult to "debug" on an
oscilloscope due to the bit stuffing and error correction, yet all but the
cheapest logic analyzers are fast enough (at least for full-speed USB @
12Mbps) to let your PC trivially do the decoding.  (Of course there are
specialized boxes/software just for USB decoding as well, and as I recall some
are even <$1k... dirt cheap for what you get.)



Re: Advice on Logic Analyzer
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OK, just curious. I'm a bit naive; how does a logic analyzer handle
the reflected wave switching thingy of PCI signals? Can it interpret
the levels correctly?

Re: Advice on Logic Analyzer
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The few that I've used let you adjust the switching threshold to either any
old voltage you liked or a handful of "common" standards.  As such, they just
don't "see" the incident wave and only transition low->high or vice versa on
the reflected wave.

Truth be told, unless you're dealing with a physically large (long time delay)
backplanes, often the incident/reflection "step" on the digital lines largely
gets swallowed up by the slew rate and loading of the drivers anyway.  On
little 4-slot MicroATX motherboards, it can be hard to see the step!  As far
as I can tell, the big emphasis on, "PCI uses reflective wave switching!"
wasn't so much because it was anything particular new or all that novel, but
rather an indicator that someone had sat down and actually thought about the
problem rather than just throwing something out there as many
then-contemporary standards such as ISA and IDE had been done or using the
brute-force high power/every line
terminated/high-velocity-cooling-fan-included-with-purchase approach that
minis and mainframes of the era were using.

---Joel



Re: Advice on Logic Analyzer

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No.

Check if the trigger logic can be programmed for what you need - for example
if you are looking for memory corruption you want to trigger on access to
the corrupted location which will be a sequence of adress words.




Re: Advice on Logic Analyzer

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I've used the logic port. It has way to little memory and it is not
very straightforward to use. If it where my money I would get the
janatek because it has 1mbit/channel memory.

--
Programmeren in Almere?
E-mail naar nico@nctdevpuntnl (punt=.)

Re: Advice on Logic Analyzer
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I've experienced that too. It is a nice simple analyzer but if you
want to do something a bit weird like sample an entire screenful of
TTL RGBI (old video standard on 8 bit computers) data it cannot do
this. With 2048 bytes per channel it can barely store one or two lines
even with compression. It just doesn't work for this application. It
does work great for looking at an entire scanline with state data from
the rest of the computer. But I needed the whole screen full. Oh well,
it's a good thing I stopped that project... :)

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