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
wire?
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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