Hey Darren -
> Thanks for the information, I have seen the exact behaviour your have
> described with the CTS control line.
> Now that you describe it I can now see what is happening. So am I to
> understand it that you dont
use the
> /dev/ttyAM ports at all and use a usb to serial adapter on port /dev/ttyUSB0?
>
> I have done this and I have also set the terminal software to 19200 8N2.
> I was not able to get 19200 8N2 to work with the /dev/ttyAM0 port, the modem
> would not
> respond to commands with readable characters.
Ah - you're right about that one. I had forgotten about the AM* issues and two
stop bits.
On my current systems, I roll my own 2.6 kernel and OS. The 2.4 kernel that TS
ships with
the board has an issue with two stop bits on the internal AMBA based ports. Our
systems
had a TS-SER1 board that we were using and that handles the two-stop bits just
fine. The
new 2.6 kernels also work great. I don't think I tried COM3 with the default
2.4 kernel.
That serial port is implemented in their FPGA and thus has a completely
different driver.
Like yourself, I was in a bind with a set of experiments that were getting set
for
deployment and ran into a wall with the lock up issue. Thinking it was a flow
control
problem, we added a SER1 board that has a real 16550 UART (not emulated) and
can do
flow control on chip. That still failed. On a lark, we tried some USB
converters and
they worked. We have a combination of pl2303 and ftdi based devices. All of
them worked
and solved the problem. I did have to backport (make that just copy over and
compile)
the latest 2.4 versions of those drivers, but that wasn't too bad of a problem.
I can
send you the binaries if you want/need them. The systems that we ended up
shipping to
the field then all used the USB solution. I didn't like it, but we were stuck.
I did
manage to find a set of cold temperature rated USB-to-serial adapters which
made things
a bit more palatable.
The two-stop bit solution was discovered after those system were deployed. We
also
saw lockup failures, although to a much less extent, with the TS7800 as well as
some
486-based PC-104 boards. It is not limited to the 7260 by any means and is a
problem
in the transceiver.
Some of my current projects require UVC based webcams onboard, which need the
latest
2.6 kernels. I have a nice buildroot-based system for compiling everything,
from the
cross-compilers, the kernel and on through the root file system. The new kernel
fixes
the /dev/ttyAM0 problem with the two-stop bits and that is the serial port we
are using
for the Iridium comms at this point.
> The USB port has yielded better results in that the connection does not lock
> up.
> However I seem to get a lot of CRC and timeouts which reduces the overall
> performance
> to about 130cps rather than the maxmimum 300cps. But at least now it does
> not just lock up and
stop.
What data services are you using from Iridium? Is this a modem-to-modem dial up?
DirectIP? RUDICS?
Are you using commercial SIMs or the US DoD gateway?
Where is your antenna located? Does it have a clear view of the sky,
horizon-to-horizon? If
part of it is blocked, then you'll be in a shadow as the satellites move across
the sky. It
only takes about 10-minutes for them to pass overhead. We've seen lots of
incidents where
you get drop outs due to the shadowing. Having said that, call drops are part
of the nature
with Iridium. On average, in the polar regions, you should see calls nowadays
last for about
20-30 minutes. That's up from what it was a few years ago.
What you shouldn't be getting are any errors. Once you've got a connection,
bytes going into
the system are almost guaranteed to come out on the other side.
With our RUDICS connections, we can stream data at the full rate (about
2500bps).
> It is not an aerial/reception problem as transmission works fine on a Windows
> to Windows setup.
> So it still must be something to do with teh TS-7260 serial interface.
What else is happening on the 7260? Writes to USB or SD? Our systems run off the
internal flash and consist of a lot of Python-based code. They are quite busy
with a number of different tasks, but we don't miss characters.
> Which model Iridiums are you using, we have a couple of 9255As but the rest
> are 9255B series :
> A3LA-XM. I seem to get varing results depending on which modem I use.
You name it, we've got it. Our research group supports the communications
aspect of the NSF polar program in the Arctic. We have a couple hundred
handsets and transceivers.
The older A3LA-D and -I models were great for cold temperature operations.
They would run down to -50C. The newer -SA models only go to -30C, but can
vary widely in that regard. We are currently testing the newer -X models.
I actually was doing that yesterday and can confirm that they are working
for our setup. We've done cold temperature testing and the ones that we
have are working at -30C, but not any lower. If you can, you definitely
need to temperature test before deployment.
The -X models are new and the various groups that I know of are just
starting to get them working. One big change has been in the amount
of power they use - much more than the SA, which hurts in these low
power setups.
> Any thoughts, have I missed something obvious?
One other place to look at is the power supply for the modem itself.
We've seen problems where you have enough current to power the modem
and talk to it, but not enough to transmit (or transmit sporadically).
Since your Windows boxes work, that probably isn't the problem unless
you are powering them differently at that point.
If you don't mind, I'm going to cc the list with this response so
people searching in the future can find it.
Regards,
Todd
--
_______________________________________________________________________
Dr. Todd Valentic SRI International
Senior Research Engineer 333 Ravenswood Ave
Center for GeoSpace Studies Menlo Park, CA 94025
E-Mail : Office: (650) 859-4642
Website: isr.sri.com Fax : (650) 322-2318
_______________________________________________________________________
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