On Thu, 27 Jun 2013 21:36:09 +0000 (UTC), Tormod Volden wrote:
Hi Tormod,
Lukasz Majewski writes:
This commit fixes problems with some non-standard requests send with device address instead of interface address (bmRequestType.Receipent field).
This happens with dfu-util (debian version: 0.5), which address non standard requests (like w_value=0x21 and bRequest=GET_DESCRIPTOR) to device.
Dear u-boot developers,
The above comment seems to imply that dfu-util is sending non-standard requests. For the record, that would be wrong. dfu-util is sending a standard "get descriptor" request. These always go to the device, not to an interface. The descriptor it is asking for is, although not mandatory per the core USB standard, a class-specific descriptor which is part of the DFU 1.0 standard. So this is all standard.
While on this topic, I would recommend that you include this descriptor in the configuration descriptor set, that is, in the complete configuration descriptor that the host OS usually requests during enumeration. Also this class-specific descriptor belongs here. In that case, the OS and libusb will keep a copy of this descriptor, and dfu-util will not have to send an explicit request (through libusb_get_descriptor()) to retrieve it.
Thanks for explanation. The commit about which we are discussing was a (reasonable) fix for the problem.
I need to look into this and came up with proper solution.
Without this fix, the above request is STALLED, and hence causes dfu-util to assume some standard configuration (packet size = 1024B instead of 4096B)
Note that this number is the "Maximum number of bytes that the device can accept per control-write transaction."
I need to check this, but AFAIR there was a problem with dfu-util (and probably libusb under the hood) version 0.1 (shipped with "ancient" old stable debian) and 0.5 which is currently in use.
The DFU transactions should work fine if a smaller packet size is used - as long as it is larger or equal to the bMaxPacketSize0. Of course, smaller packets will cause more overhead and be less efficient, but you must make sure that your device can handle this. I am not sure from these comments whether the smaller packet size caused errors in your implementation, or if the problem was just reduced performance.
The change was driven by the need to improve performance, when downloading large files (with roofts) and to silent warning on the dfu-util side.
Best regards, Tormod Volden
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