Alan Stern wrote:
On Tue, 8 Feb 2011, Arvid Brodin wrote:
With the EHCI host controller:
=============================
[Terminal 1]
$ cat /dev/ttyUSB1
[Terminal 2]
$ echo "Something seems wrong here" > /dev/ttyUSB0
$ echo "Something seems wrong here" > /dev/ttyUSB0
[Terminal 1]
Something seems wrong here
Something seems wrong here
^C
$
Observe the extra new line after the strings. I'm not sure if this is a
bug in the ftdi driver, some other part of the serial subsystem, or if
it is the result of some terminal setting; with a USB analyzer I observe
the following sequence of packets (#-# == device-endpoint):
3-2 OUT: "Something seems wrong here"
3-2 OUT: 0x0D 0x0A
4-1 IN: 0x01 0x60 'S'
4-1 IN: 0x01 0x60 'o'
...
4-1 IN: 0x01 0x60 0x0D
4-1 IN: 0x01 0x60 0x0A
4-2 OUT: 'S' # The echo from the reading side starts here
4-2 OUT: 'o'
...
4-2 OUT: 0x0D 0x0A
4-2 OUT: 0x0D 0x0A # The newline pair is echoed twice - perhaps both
'CR' and 'NL' are converted to "CRNL" in the echo?
Not exactly -- CR is changed to NL upon input. That's what "icrnl"
means in your stty output.
Ok... so this is a bug then? The echo should really be 2x0A instead of
2x0D0A?
No, it's not a bug. The echo should be 0x0D 0x0A 0x0D 0x0A, which is
what it is. Upon output, each NL is converted to CR NL; that's what
"onlcr" means in the stty output.
I see. Thanks for explaining this!
Ok, I made another run, this time saving the usbmon output as well:
[Terminal 1]
# cat /dev/ttyUSB1
[Terminal 2]
# echo "This is isp1761 and something is wrong" > /dev/ttyUSB0
# echo "This is isp1761 and something is wrong" > /dev/ttyUSB0
# echo "This is isp1761 and something is wrong" > /dev/ttyUSB0
#
[Terminal 1]
This is isp1761 and something is wrong
761 and something is wrong
7This is isp1761 and something is wrong
61 and soThis is isp1761 and something is wrong
7This is isp1761 and something is T
^C
#
The usbmon dump shows this (ttyUSB0 is dev 4, ttyUSB1 is dev 5; endpoint
1 is the input stream and endpoint 2 is the output stream for each
serial port):
1) The string is output on ttyUSB0:
93a7b100 426649297 S Bo:1:004:2 -115 38 = 54686973 20697320 69737031 etc...
93a7b100 426652018 S Bo:1:004:2 -115 1 = 0d
93a7b100 426652343 C Bo:1:004:2 0 1 >
93a7b100 426652576 S Bo:1:004:2 -115 1 = 0a
(lots of NAKs on the bus here, and no callback just yet)
2) The string is received by 5-1 in three bulk IN transfers and echoed
one char at a time on 5-2. The CRNL pair is doubled.
3) Then, just after the setup packets to 4-0 for the next 'echo',
something interesting happens:
93971d00 427486550 S Bi:1:004:1 -115 512 <
93971d00 427487171 C Bi:1:004:1 0 32 = 01603736 3120616e 6420736f
6d657468 696e6720 69732077 726f6e67 0d0a0d0a
Note that this is the "761 and something is wrong" and multiple CRNL
from the 'cat' above. This is then echoed from 4-2 and again every CRNL
pair gets doubled to CRNLCRNL.
So your loopback setup is causing the echo from the second port to be
re-echoed by the first port. Maybe it would help if you disabled
echoing on the first port: stty -F /dev/ttyUSB0 -echo.
As far as I can see, the only question is why you did get the echoing
under one kernel and didn't get it under the other.
Yes, and why only part of the text gets echoed. Perhaps it is a timing
issue? Anyway, unless someone wants me to continue digging into this, I
consider this (the echo problem) solved now. Thanks!
--
Arvid Brodin
Enea Services Stockholm AB
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