Sorry, this was intended for the linux-usb list. -- Arvid Arvid Brodin wrote: > Hi! > > I get weird problems when I use a null modem cable between the two ports > on a FT232BM (2-port FTDI USB-to-serial converter) with an isp1761 host > controller. The same thing does not happen with an EHCI host controller. > Lengthy details follows: > > 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? > > Anyway, since 3-1 is never read, no feedback loop is created by the two > echoing devices. > > > With the isp1761 host controller, driver from 2.6.35.7 backported to > 2.6.27.54 and modified for platform endianness: > ============================= > > [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 > # 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 > > This is isp1761 and something is wrong > > This is isp1761 and something is wrong > > This is isp1761 and something is wrong > > This is isp1761 and something is wrong > > and something is wrong > (blank line x7) > This is isp1761 and something is wrong > > ^C > # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 > # cat /dev/ttyUSB1 > is wrong > (blank line x30 ca) > TThis is isp1761 and something is wrong > > ^C > # > > The exact look of the error differs, but it is quite easy to trigger by > echoing text several times in a row; also breaking the "cat" execution, > echoing some more text, and then starting cat again seems to trigger the > error often. > > On the bus the traffic looks something like this: > > 7-2 OUT: "This is isp1761 and something is wrong" > 7-2 OUT: 0x0D > 7-2 OUT: 0x0A (NAK) # The CRNL pair is split here and the NL is not > directly accepted by the device > 7-2 OUT: 0x0A (NAK) > Following this is lots and lots of "0x0A NAKs" intermixed with traffic > that looks quite like the EHCI case except that much of the traffic has > to be re-sent lots of times before it is accepted. The 0x0A is finally > accepted after all text has been received by 8-1 and echoed from 8-2. > This exact pattern is repeated every time text is written to the serial > port. > > Device 8 receives the characters and echoes them back to 7-1 as in the > EHCI case. But with isp1761, after a while device 7 for some reason > starts echoing parts of the received echo-text back. My guess is that > this should not happen since device 7 is never read from. Anyway, this > creates a feedback loop which would be the source of the spurious > characters in the "cat" run above and that sometimes is powerful enough > to make the terminal unresponsible. > > I've been trying to figure this thing out for a while now but quite > frankly I'm stumped; I can't figure out where and why things goes wrong. > Any ideas are welcome! Perhaps the NAK problem/bug triggers a > problem/bug somewhere in linux' serial terminal code? > > The terminal settings are the defaults and are the same during all > examples above on both serial ports: > > $ stty -a -F /dev/ttyUSB0 > speed 9600 baud; rows 0; columns 0; line = 0; > intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; > eol2 = <undef>; swtch = <undef>; > start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; > flush = ^O; min = 1; time = 0; > -parenb -parodd cs8 hupcl -cstopb cread clocal -crtscts > -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon > -ixoff -iuclc -ixany -imaxbel > -iutf8 > opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 > vt0 ff0 > isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop > -echoprt echoctl echoke > > $ stty -g -F /dev/ttyUSB0 > 500:5:cbd:8a3b:3:1c:7f:15:4:0:1:0:11:13:1a:0:12:f:17:16:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0 > > -- > Arvid Brodin > Enea Services Stockholm AB > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@xxxxxxxxxxxxxxxxx > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
