[linux-usb-devel] [usb-serial] Character loop

Aman, Magnus Thu, 28 Jul 2005 17:47:17 -0700

Hi,

I wonder what common pitfall I have encountered (?) but seek help nevertheless.

=== Problem ===

Sending "AT" to the modem, it echoes back "A". But before the "T" comes in, my driver sends out an "A" again in a blocking loop!

My termios are picked to disable echo and allow sending without involvement of CR LF of any kind.

I suspect termios having something to do with the problem anyway but so a confirmation/solution is welcome.

=== General info ===

Kernel 2.6.9, under /drivers/usb/serial I use a slightly modded usb serial generic driver (added USB controls for enabling the modem).

=== Termios altered by my application ===

void init_comm(struct termios *ptio)

{

ptio->c_lflag &= ~ICANON;

ptio->c_lflag &= ~(ECHO | ECHOCTL | ECHONL);

ptio->c_cflag |= HUPCL;

ptio->c_cc[VMIN] = 1;

ptio->c_cc[VTIME] = 0;

/* Standard CR/LF handling: this is a dumb terminal.

* Do no translation:

* no NL -> CR/NL mapping on output, and

* no CR -> NL mapping on input.

ptio->c_oflag |= ONLCR;

ptio->c_iflag &= ~ICRNL;

ptio->c_cflag |= CRTSCTS;

ptio->c_iflag &= ~(IXON | IXOFF | IXANY);

cfsetospeed(ptio, B9600);

cfsetispeed(ptio, B9600);

}

=== USB debug messages with comments ===

/home #
/home # mknod /dev/ttyUSB0 c 188 0
/home # ./wmlink_test /* Application starts with ttyUSB0 open method */

<7>drivers/usb/serial/usb-serial.c: serial_open

/* Here the initial four vendor specific USB control transfer debug messages have been removed */

<7>drivers/usb/serial/generic.c: usb_serial_generic_open - port 0

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf420 dev=7 ep=1in-bulk flags=0 len=0/64 stat=-115

wmlink> +AT /* Application places "AT" in transfer buffer and start a write cycle */

Added 2 characters
wmlink> -x /* Application sends transfer buffer [0x41 0x54 0x00] via ttyUSB0 write method */

<7>drivers/usb/serial/usb-serial.c: serial_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - returns 64
<7>drivers/usb/serial/usb-serial.c: serial_write - port 0, 2 byte(s)
<7>drivers/usb/serial/generic.c: usb_serial_generic_write - port 0
<7>generic ttyUSB0: usb_serial_generic_write - length = 2, data = "" 54

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf480 dev=7 ep=1out-bulk flags=0 len=0/2 stat=-115
<7>drivers/usb/host/ohci-dbg.c: data(0/2): 41 54 stat:-115
<7>drivers/usb/serial/usb-serial.c: serial_write_room - port 0
<7>drivers/usb/host/ohci-dbg.c: RET c0baf480 dev=7 ep=1out-bulk flags=0 len=2/2 stat=0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_bulk_callback - port 0
<7>drivers/usb/serial/usb-serial.c: usb_serial_port_softint - port 0

/* Here "AT" write cycle has been sent out and been acknowledged by modem */

<7>drivers/usb/host/ohci-dbg.c: RET c0baf420 dev=7 ep=1in-bulk flags=0 len=1/64 stat=0
<7>drivers/usb/host/ohci-dbg.c: data(1/64): 41 stat:0
<7>drivers/usb/serial/generic.c: usb_serial_generic_read_bulk_callback - port 0
<7>generic ttyUSB0: usb_serial_generic_read_bulk_callback - length = 1, data = ""

/* Here the first echoed character "A" has returned from modem*/

/* Below a single "A" character is sent out unexpectedly. ((Why this?)) */

<7>drivers/usb/serial/usb-serial.c: serial_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - returns 64
<7>drivers/usb/serial/usb-serial.c: serial_write - port 0, 1 byte(s)
<7>drivers/usb/serial/generic.c: usb_serial_generic_write - port 0
<7>generic ttyUSB0: usb_serial_generic_write - length = 1, data = ""

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf480 dev=7 ep=1out-bulk flags=0 len=0/1 stat=-115
<7>drivers/usb/host/ohci-dbg.c: data(0/1): 41 stat:-115

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf420 dev=7 ep=1in-bulk flags=0 len=0/64 stat=-115

/* Below a second "A" write cycle begins before the RET of the previous transmission. */

/* This time not passing serial_write_room but only the generic driver method ((??)) */

<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - port 0

<7>drivers/usb/host/ohci-dbg.c: RET c0baf420 dev=7 ep=1in-bulk flags=0 len=1/64 stat=0
<7>drivers/usb/host/ohci-dbg.c: data(1/64): 54 stat:0
<7>drivers/usb/serial/generic.c: usb_serial_generic_read_bulk_callback - port 0
<7>generic ttyUSB0: usb_serial_generic_read_bulk_callback - length = 1, data = ""

/* Here the second echoed character "T" has returned from modem*/

/* Here the second "A" write cycle is stalled; 'no room'. */

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf420 dev=7 ep=1in-bulk flags=0 len=0/64 stat=-115

<7>drivers/usb/host/ohci-dbg.c: RET c0baf480 dev=7 ep=1out-bulk flags=0 len=1/1 stat=0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_bulk_callback - port 0
<7>drivers/usb/serial/usb-serial.c: usb_serial_port_softint - port 0

/* Here the first single "A" write cycle is finished. */

/* Here the modem echoed back the first single "A" being sent. */

/* Below the second single "A" write cycle restarts. */

<7>drivers/usb/serial/usb-serial.c: serial_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - returns 64
<7>drivers/usb/serial/usb-serial.c: serial_write - port 0, 1 byte(s)
<7>drivers/usb/serial/generic.c: usb_serial_generic_write - port 0
<7>generic ttyUSB0: usb_serial_generic_write - length = 1, data = ""
<7>drivers/usb/host/ohci-dbg.c: SUB c0baf480 dev=7 ep=1out-bulk flags=0 len=0/1 stat=-115
<7>drivers/usb/host/ohci-dbg.c: data(0/1): 41 stat:-115

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf420 dev=7 ep=1in-bulk flags=0 len=0/64 stat=-115

/* Below a third "A" write cycle begins before the RET of the previous transmission. */

/* This time not passing serial_write_room but only the generic driver method ((??)) */

<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - returns 0
<7>drivers/usb/host/ohci-dbg.c: RET c0baf480 dev=7 ep=1out-bulk flags=0 len=1/1 stat=0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_bulk_callback - port 0
<7>drivers/usb/serial/usb-serial.c: usb_serial_port_softint - port 0

/* Here the second single "A" write cycle is finished. */

/* Here the modem echoed back the second single "A" being sent. */

/* Below the third single "A" write cycle restarts. */

<7>drivers/usb/serial/usb-serial.c: serial_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - returns 64
<7>drivers/usb/serial/usb-serial.c: serial_write - port 0, 1 byte(s)
<7>drivers/usb/serial/generic.c: usb_serial_generic_write - port 0
<7>generic ttyUSB0: usb_serial_generic_write - length = 1, data = ""
<7>drivers/usb/host/ohci-dbg.c: SUB c0baf480 dev=7 ep=1out-bulk flags=0 len=0/1 stat=-115
<7>drivers/usb/host/ohci-dbg.c: data(0/1): 41 stat:-115

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf420 dev=7 ep=1in-bulk flags=0 len=0/64 stat=-115

<7>drivers/usb/serial/usb-serial.c: usb_serial_port_softint - port 0
<7>drivers/usb/host/ohci-dbg.c: RET c0baf480 dev=7 ep=1out-bulk flags=0 len=1/1 stat=0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_bulk_callback - port 0
<7>drivers/usb/serial/usb-serial.c: usb_serial_port_softint - port 0

<7>drivers/usb/serial/usb-serial.c: serial_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - port 0
<7>drivers/usb/serial/generic.c: usb_serial_generic_write_room - returns 64
<7>drivers/usb/serial/usb-serial.c: serial_write - port 0, 1 byte(s)
<7>drivers/usb/serial/generic.c: usb_serial_generic_write - port 0
<7>generic ttyUSB0: usb_serial_generic_write - length = 1, data = ""
<7>drivers/usb/host/ohci-dbg.c: SUB c0baf480 dev=7 ep=1out-bulk flags=0 len=0/1 stat=-115
<7>drivers/usb/host/ohci-dbg.c: data(0/1): 41 stat:-115

<7>drivers/usb/host/ohci-dbg.c: SUB c0baf420 dev=7 ep=1in-bulk flags=0 len=0/64 stat=-115

Kind regards, Magnus Aman [EMAIL PROTECTED]

Texas Instruments Sweden

[linux-usb-devel] [usb-serial] Character loop

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