usb problems

[Nils Kassube]

Gene Heskett wrote:
> On Sunday 12 October 2014 07:37:21 Gene Heskett did opine
> And Gene did reply:
> > On Sunday 12 October 2014 02:41:15 Nils Kassube did opine
> > And Gene did reply:
> > > Gene Heskett wrote:
> > > > I am in need of a tool that will effectively do a ping against a
> > > > specified USB port, a port I know there is something on the
> > > > other
> > > > end of the cable and hub as I just had a printer do a test page
> > > > over the same cabling. Basically I want to send a $55 down the
> > > > cable once a second to a specified port, in thgius case
> > > > /dev/ttyUSB1, for oscilloscope troubleshooting, at least as long
> > > > as trouble doesn't shoot back... ;-)
> > > 
> > > If that /dev/ttyUSB1 device is a USB->serial converter, you could
> > > treat it like any terminal device. Therefore, you can use stty to
> > > disable the handshaking lines and set the desired speed (e.g. 100
> > > Baud). Then echo the desired characters to the device:
> > > 
> > > stty -F /dev/ttyUSB1 clocal ospeed 100
> > 
> > stty -F /dev/ttyUSB1 clocal ospeed 115200
> > stty -F /dev/ttyUSB1 clocal ispeed 115200

That should be possible with a single line:

stty -F /dev/ttyUSB1 clocal ospeed 115200 ispeed 115200

> > This works, I can see the once a second red led flicker.  But when
> > measured with the scope, the baud rate seems to be about 55800 (not
> > 57600) unless that "e" is a 2 bits high, 2 bits low etc character.

My fault - like Colin wrote already, it should be "U" instead of "e". 
But if you measure the entire character time from the start bit to the 
end, the exact value should not matter.

> and after trying to use it at 115200, something is resetting it to
> 9600?

Not here - maybe something else resets your device, but not the shell. 
Did you check it with

stty -F /dev/ttyUSB1 -a

or how do you know it is at 9600?

> I've taken the serial cable apart, its well soldered on both ends, and
> I've tried the 2nd of 2 identical converters, converters that worked
> just fine in April of this year.  Data is coming out of the CoCo3
> with about a 10 volt p-p swing centered on ground.  Humm, come to
> think about that, thats low,

No, it isn't. Usually the power for the converter comes from the 5V of 
the USB port with a voltage inverter, so 10 Vpp is fine.


Nils