On Thu, Jul 19, 2007 at 07:54:22PM +0200, Alain Degreffe wrote:
> I have a newbie question :-)
>
> I would like to have to threads: 1 reading process and one writing
> process...
>
> For the moment as soon I write to device, I begin to read the answer but it
> is not very efficient because the iso7816 don't give a real way to know if
> the write is finish or if the read will give an answer...
>
> In the usb-serial classical implementation, the bulk read return all
> incoming characters and the callback function permit to write those
> characters into the tty device. In my case, the problem is the next one: to
> read character I must send a command to the device with a bulk write.. In
> the read call back, may I use the port stored in the context to call a bul
> write function to ask to the device to read ?
Look at how other drivers do it, they kick off the read urb all the time
while the port is open. That's the only way to ensure that they always
are getting the data from the device.
> Second problem, the protocol of the device works like this: To read
> character, I must ( as I said before ) , send a command to read ( a bulk
> write message ) , after try to read one byte to know how much byte are
> waiting in the device buffer and finally bulk read the len given at the
> previous step...
>
> So ideally, a thread dedicated to this sequence is the solution to the
> latency observed in the current implementation ( the smart routine is not
> magic and the cases to stop waiting are limited ) because the function wait
> during 200 round to be sure to read all datas...
Yes, just keep kicking off a read urb to do this. The sequence will
probably be:
1) send write command in urb
2) when command urb completes send read urb.
3) when read urb completes go to step 1
and yes, it is safe to submit other urbs from within an urb callback.
Hope this helps,
greg k-h
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