Re: [Linux-usb-users] USB: Non zero status

On Sat, 18 Aug 2007, Martin Bachem wrote:

> > I don't understand.  Are you talking about TX URBs?  How can you have 
> > too much pending data?  What are the intervals of the Iso endpoints?
> > It shouldn't be possible to send too much data for the device to 
> > handle.
> 
> 
> yes, it's about TX frames... The ISDN controller working within the
> device is a HFC-S USB (http://www.colognechip.com/hfc-s-usb.pdf ), which
> has a very small Fifo of 128 Bytes. If I start filling the beginning of
> an HDLC Frame into the Fifo, the fifo starts emptying this one to line
> interface immetiately. If the Fifo runs empty, it terminates the HDLC
> Frame. So I need to make sure the Fifo is well filled during the
> transmission of one HDLC frame. This is the matter: as long is the
> controller is transmitting one Frame, I need to keep the fifo well
> filled with this frame data, but have to make sure to produce no overun.
> 
> I configure each Fifo's fill level threshold to 64 bytes. The status
> info of 'threshold reached' is signalled by a state byte in the RX URBs.
> So at the time I care about the threshold reached bit (tx ISO
> completion), its outdated.
> The next issue is I do not know at what speed the fifo is emtied to line
> interface. The line interface speed is fixed to 8 byte per ms, but due
> to HDLC encoding the data amout gets increased by an unkown value (I
> could do software HDLC encoding to know exactly, but I want to avoid that).
> 
> So I start transmitting an HDLC frame by putting 8 bytes per ms in TX
> ISO URBs. As soon as I realize by analyzing the RX URBs that threshold
> is reached, I continue the TX stream by writing just 6 bytes into each
> ISO packet. This way I hope to alternate betweeen threshold reached and
> fill level below threshold smoothly, without messing with the fifos
> boundries...

You haven't answered my question about the Iso endpoints.  Please 
post the "lsusb -v" output for the device.

Alan Stern


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