[Nut-upsdev] usbhid-ups fails with Belkin F6C120-UNV in nut-2.4.3

Charles Lepple clepple at gmail.com
Sat Mar 20 21:02:37 UTC 2010

On Mar 20, 2010, at 3:19 PM, Jon Burgess wrote:

> It appears that this UPS is a low speed device and the USB standard
> seems to say these only support transactions of up to 8 bytes in  
> length
>  usb 7-1: new low speed USB device using uhci_hcd and address 2
> There are a few mentions of 8 bytes in the lsusb output for the  
> device:

I haven't done much work with usbmon - is it showing the size of the  
transaction as requested by the application, or what goes out over the  

Along those lines, what kernel version are you using? Are you using  
libusb-0.1.x, or the 0.1 compatibility layer from libusb-1.0?

Several years ago on the linux-usb list, it was often pointed out that  
the kernel was supposed to honor the wMaxPacketSize field, and  
fragment the requests accordingly. While this was suggested for  
performance reasons (fewer round trips between user and kernel space),  
it should still hold true for less frequent transfers.

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