On Saturday 30 March 2013 03:20:15 Mike Verstegen wrote:
> - Downloaded the source code for the cdc_acm driver.
> - Added a bunch of printk debug messages and stack_dumps to follow what's
> going on.
> - I rmmod'd the "stock" cdc_acm and insmod'd my instrumented module.
> - All the device enumeration works, right driver attached, etc.
> - Since the code works on Ubuntu 12.04/Linux 3.2, I grabbed the 3.2 cdc_acm
> code and compiled that module on the Centos 6 / Linux 3.6 platform. Using
> that 3.2 module instead of the 3.6 module did not make a difference. I
> reverted to the 3.6 module.
> - Turned on the debug file system with usbmon and watched the USB traffic.
> I can see that there are extra characters being sent on the USB interface.
> - To watch what's going on, on top of the printk's in the cdc_acm module,
> I've merged the output of usb mon (cat /sys/kernel/debug/usb/usbmon/3u |
> logger) and the output of the test application (scan_example /dev/ttyACM0 |
> logger -s) so I have a single stream of time correlated debug trail.
> - The spurious characters sent on the USB endpoint are x5E x40 x5E x40 x5E
> x40 x5E x40 x41 (in ASCII its ^@^@^@^@A ) which looks like some sort of
> probing or trying to get the attention of a modem These characters are sent
> immediately after the application's write() causes the 4 hello bytes to be
> sent to the end point.
To clarify, is acm_tty_write() called with the additional bytes or isn't it?
Regards
Oliver
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
