Re: [libusb] Asynchronous transfer using libusb-1.0 on ubuntu

[Tim R. <ti...@pr...>]

Anand Nahar wrote:
>
> Why?  Not trying to be snotty, but if you're reading large blocks, the
> gain from asynchronous processing is not that large.
>
>   * I was wondering, if I have multiple asynchronous transfers lined
>     up, it would utilize the bandwidth all the time (may be 2 or more
>     transfers overlap) and not wait for the next transfer to be
>     initiated. I just wanted to make sure that there is no idle
>     periods in between 2 consecutive transfers. Right now I have
>     multiple threads transferring data synchronously to different
>     devices but this still doesn't guarantee no idle period.
>

You can't have overlapping transfers.  Remember that the model
anticipates physical devices, which have one read head that can only be
one place at a time.  It's all serialized.


> "can I submit a second CBW before the first transfer is complete?
>
>   * I have actually tried this. I submit multiple CBW’s and read the
>     data in their callback functions. It doesn’t seem to work and I
>     understand why that doesn’t work. I was curious on whether there
>     is some other approach to this.
>

I'm a little surprised by that.  I would have expected you could submit
CBW, read, CBW, read, in that order, all in advance, and it work just
fine.  However, as I said, I couldn't find support in the spec for that.

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.