Cross talk on serial ports

[Stephen Bridges-3]

I have a verdex and robostix (and netwifi) combination, and access the
serial ports via the robostix.  When I run my app that sends lots of data
out of /dev/ttyS2 to another processor, I get garbage on ttyS0, corrupting
my serial console.  Keystrokes are being received, as I can run commands
from history and see that they are enacted, but the output is garbled.

The problem starts and stops when writing to ttyS2.

Stephen.


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[Dave Hylands]

Hi Stephen,

> I have a verdex and robostix (and netwifi) combination, and access the
> serial ports via the robostix.  When I run my app that sends lots of data
> out of /dev/ttyS2 to another processor, I get garbage on ttyS0, corrupting
> my serial console.  Keystrokes are being received, as I can run commands
> from history and see that they are enacted, but the output is garbled.
>
> The problem starts and stops when writing to ttyS2.

I've never experienced this particular problem with any of my robostix
boards (I have about a half dozen or so).

I'd check to make sure you've got good solid grounds. Is your console
connected to the GUMSTIX connector on the robostix?

Which revision of robostix do you have?

It's possibly due to a defective board. I took a look at the 1131
board layout, and there is one spot on the board where a via from the
Y0_TXD signal (console Tx) transitions from the top layer to an
internal layer, and is right next to a trace of the IR_TXD (which is
on the bottom layer). Otherwise the signals aren't even close to each
other.

If it is a defective board, then it's also quite possible that
transmissions on the console would also mess up the output on ttyS2.
Do you see any evidence of that?

Do you have any other daughter cards you could try? This would at
least help to extablish that the problem is with the robostix and not
the motherboard.

--
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

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[Stephen Bridges-3]

> I'd check to make sure you've got good solid grounds. Is your console
> connected to the GUMSTIX connector on the robostix?

Yes it is.

> Which revision of robostix do you have?

The 1131.

> If it is a defective board, then it's also quite possible that
> transmissions on the console would also mess up the output on ttyS2.
> Do you see any evidence of that?

I've not looked for it, I only use the console when I get other problems
(which I'll start a separate topic about).

> Do you have any other daughter cards you could try? This would at
> least help to extablish that the problem is with the robostix and not
> the motherboard.

I have a netwifi and tweener - obviously the tweener can't be inserted in
all that, and indeed wouldn't fit in the box made for it now.  I'll put a
scope on the line and look for noise when transmitting on the other serial
port.

Stephen.


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[Stephen Bridges-3]

On Tuesday 08 July 2008 10:03:59 Stephen Bridges wrote:

> I have a netwifi and tweener - obviously the tweener can't be inserted in
> all that, and indeed wouldn't fit in the box made for it now.  I'll put a
> scope on the line and look for noise when transmitting on the other serial
> port.

Interestingly, I can't see anything obviously wrong with the voltage levels.  
RS232 is such a pain, I have a slight suspicion that something weird is
happening, like my program that outputs on ttyS2 is reconfiguring ttyS0 and
mangling its baud rate.  Out of interest, how many instances of getty do you
have spawned?  I get one spawned at 38400 baud, which is interesting when the
serial console is running at 115200.

Stephen.

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