[PD] Comport and UBW problems on Linux

Martin Peach martin.peach at sympatico.ca
Thu Oct 11 05:55:26 CEST 2007

Thomas O Fredericks wrote:
> I am creating an abstraction to ease the communication with an UBW 
> (USB Bit Wacker: http://greta.dhs.org/UBW/index.html 
> <http://greta.dhs.org/UBW/index.html>).
> The abstraction uses comport to communicate with the device. It is 
> considered as USB modem by the system. See the tail of dmesg when the 
> device is plugged in to my Ubuntu machine:
> [102406.169656] usb 1-5: new full speed USB device using ohci_hcd and 
> address 8
> [102406.381592] usb 1-5: configuration #1 chosen from 1 choice
> [102415.654264] usb 1-5: USB disconnect, address 8
> [102416.484598 ] usb 1-5: new full speed USB device using ohci_hcd and 
> address 9
> [102416.706005] usb 1-5: configuration #1 chosen from 1 choice
> [102416.708971] drivers/usb/class/cdc-acm.c: This device cannot do 
> calls on its own. It is no modem.
> [102416.708984] cdc_acm 1-5:1.0: ttyACM0: USB ACM device
> The problem is as follows:  The abstraction works fine in XP,
> but in Ubuntu,
> when I want to send more than three values
> (i.e. something like [77,65,49,42,13< ),
> comport complains that:
> "[comport] write returned -1, errno is 11
> Write error, maybe TX-OVERRUNS on serial line"
 From an errno.h:

#define	EAGAIN		11	/* Try again */

Maybe try sending the bytes one at a time slowly?
I'm guessing that EAGAIN means the data has not been sent yet, it's still in the queue.
I think it works in the XP version because write_serial() explicitly checks for an ERROR_IO_PENDING.
But the result should be the same, the data gets sent anyway, the error is bogus.
If that's the problem I'll fix it tomorrow in cvs.


> Now, ttyACM0 is a weird device because it does not have a baud rate. 
> It simply sends the data as fast as it can. So, this message DOES not 
> make any sense.
> I know it is not a problem with my configuration of Ubuntu because I 
> was able to establish proper communication with Perl.
> Anybody have a clue on how to solve this or modify comport? (I used a 
> version I compiled from pd cvs and another from pd-extended and both 
> failed).
> Tom
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