Re: PROBLEM: USB ACM device does not work

[Alan Stern]

On Wed, 1 Jul 2009, Arseniy Lartsev wrote:

> On Tuesday 30 June 2009 11:22:04 Oliver Neukum wrote:
> > Yet, your device shows bulk endpoints. Please enable DEBUG in cdc-acm.c
> > and recompile with CONFIG_USB_DEBUG.
> 
> I've recompiled four modules usbcore, ehci_hcd, ohci_hcd and cdc-acm with -DDEBUG.
> Here is kernel log:
> 
> ======================== Device plugged in ========================
...
> Jun 30 23:58:35 noteb00k kernel: usb 2-3: new low speed USB device using ohci_hcd and address 5                        
...
> Jun 30 23:58:35 noteb00k kernel: usb 2-3: config 1 interface 1 altsetting 0 endpoint 0x1 is Bulk; changing to 
> Interrupt
> Jun 30 23:58:35 noteb00k kernel: usb 2-3: config 1 interface 1 altsetting 0 endpoint 0x81 is Bulk; changing to 
> Interrupt                                                                                                                      

This looks like your problem.  Low-speed devices are not allowed to 
have bulk endpoints.  Linux internally changes them to interrupt 
endpoints with interval = 1 and maxpacket size no larger than 8.

Alan Stern

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