Re: [libusb] USB Host to Host Bridge Cable with Prolific PL25A1 chip question

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

Isaachsen, Erin K. wrote:
> Yes.  I would like to create my own application to transfer messages over this cable from between hosts.    
>
> On Host A we have an app that does a libusb_bulk_transfer (with a long timeout) on the IN Bulk Transfer Endpoint (0x83) and it blocks.  Then on Host B we have an app that does a libusb_bulk_transfer on the OUT Bulk Transfer Endpoint (0x02).  The Host A app never gets the transfer and eventually times out.
>
> Using this Data Sheet for the chip: http://prolificusa.com/files/ds_pl25A1B_v1.0B.pdf 
>
> There is another endpoint indicated in the Data Sheet, Endpoint 1 IN, Interrupt Transfer, but it is not clear how that is involved in getting data to go back and forth on the Bulk Transfer endpoints.  The cable is advertised as being expressly made for the Windows Easy Transfer Program; it does work with that. 

It's not impossible that there is a protocol involved here, so that the
bulk packets have to have some kind of header to exchange information. 
I'm guessing the interrupt pipe is used to notify one end when data is
available.  Waiting on an interrupt pipe is much more efficient than
waiting on a bulk pipe, which ends up flooding the bus with continuous
IN requests.

You're poking in the dark.  Have you tried using a bus monitor to see
what actually happens in the "Easy Transfer" process?

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