Re: [Discuss-gnuradio] max capacity per USB channel

[Eric Blossom]

On Mon, Apr 09, 2007 at 04:24:23PM -0400, George Nychis wrote:
> Eric Blossom wrote:
> >Uhh, 30 requests of .5 is only 15MB/s, so there would be no problem
> >with additional requests up to an additional 17MB/s.  The tx and rx
> >channels are allocated indepently of each other, though all capacity
> >requests are changed against the same pool.
> 
> Right, it was part of the example.
> 
> Based on your response... I think we have a problem with our interface.

Take a look at usrp/host/lib/inband/usrp_server.mbh.
That's the real interface.  FYI, I've put a note in
inband-signaling-usb-host pointing to that file.


;; ----------------------------------------------------------------
;; usrp-channel
;;
;; The protocol class is defined from the client's point-of-view.
;; (The client port is unconjugated, the server port is conjugated.)

(define-protocol-class usrp-channel

  (:outgoing

   (cmd-allocate-channel invocation-handle capacity-reservation)

   ;; The cmd-allocate-channel message requests that the server
   ;; allocates a logical channel in the FPGA for use.
   ;; capacity-reservation specifies the number of bytes/s of
   ;; interconnect capacity (USB or ethernet) to reserve for this
   ;; channel.  (The reservation is just a sanity check, no OS
   ;; specific mechanism is used.)

   (cmd-deallocate-channel invocation-handle channel)

   ;; The integer channel specifies the channel to deallocate.

   )

  (:incoming


   (response-allocate-channel invocation-handle status channel)

   ;; If successful, a channel the specified capacity was allocated.
   ;; channel, an integer, indicates which channel was allocated.

   (response-deallocate-channel invocation-handle status)

   ;; If successful, the specified channel and associated interconnect
   ;; capacity were deallocated.

   )
  )


> Regardless of whether we return a channel to the user, or the user 
> specifies a desired channel...
> 
> How does cmd_deallocate_channel() know how much to de-allocate?

It deallocates the amount that was originally allocated.  What's the problem?

> If these  are hardware channels we are talking about (currently 2 in 
> hardware), and I 
> now want to deallocate my channel and i say cmd_deallocate_channel(blah, 1) 
> ... I am going to deallocate all of channel 1 which is incorrect. The 
> capacity I reserved should be deallocated.

I think there's some confusion here.  When a user requests an rx or tx
channel with (cmd-allocate-channel invocation-handle
capacity-reservation), they are given a channel on an exclusive basis.
The returned channel number is given in the response-allocate-channel
message.

When they send (cmd-deallocate-channel invocation-handle channel) the
server (after checking that this port actually _does_ own channel)
frees the channel and gives the associated capacity reservation back to
the pool.

> So then is it required for the requester to keep track of how much they 
> requested to pass to our deallocation method?

No, the server keeps track of how much it assigned to each rx and tx
channel.

Does this make sense?

Eric