On Wed, 30 Mar 2005, Alan Stern wrote:
> On Tue, 29 Mar 2005, Jan Merka wrote:
>
> > On Tuesday 29 March 2005 04:16 pm, jklaas wrote:
> > > I have another question that I don't quite understand. With the FM Radio
> > > the TransferBufferLength in the URB going down is usually either 0x16 or
> > > 0xca. The URB coming back has the TransferBufferLength is 0x06. I
> > > guess I don't quite understand why they're different.
> >
> > In one direction (OUT or "goind down" in sniffusb's terminology), the length
> > of the buffer depends on the size of the command that you are sending to the
> > device. On the way back (IN or "going back"), the size tells how may bytes
> > were sent back by the device as a response to the received command. Assuming
> > that you don't have a description of those commands, the trick is to figure
> > out what they mean (and the responses).
>
> More accurately, for an OUT transfer (sending data to the device) the two
> lengths should be the same unless an error occurs. For an IN transfer
> (reading data from the device), the "going down" length indicates how much
> data the computer asked for whereas the "coming back" length indicates how
> much data the device actually sent. It's not an error for a device to
> send less data than it was asked for.
OK, I was just seeing different lengths being asked for depending on
whether the tuner was "idle" (the radio program was sending "no_op"s)
and when the program was tuning the radio. Somehow I thought that was
significant. Is it possible the device is somehow picking up on the
size request sent and interpreting that as some sort of command code?
> Alan Stern
>
>
--
James Klaas
Windows 95 - 32 bit extensions and a graphical shell for a 16 bit patch to an
8 bit operating system originally coded for a 4 bit microprocessor, written
by a 2 bit company that can't stand 1 bit of competition.
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