On 4/23/07, Alan Stern <[EMAIL PROTECTED]> wrote:
> On Mon, 23 Apr 2007, nesta wrote:
>
> > hi all,
> > i have 2 questions:
> >
> > 1) i make simple while loop,at the host side, in which i m receiving the
> data
> > using the read function of usb-skeleton module,it is as follows:
> >
> ***************************************************************************
> > do
> > {
> > insize =read (fd,(char*)inbuff, sizeof (inbuff) );
> > printf("insize is %d\n",insize);
> > printf(" %s\n",inbuff);
> > }while (strcmp(inbuff,"end"));
> >
> ****************************************************************************
> > my aim is : when the gadget has something to send to the host this while
> loop
> > will print what the hosts receives from the gadget.
> >
> > but this does not happen when i use the skel_read function,it is in
> > usb-skeleton.c,as when the gadget does not have anything to send to the
> host,i
> > found that the read function is non-blocking and it prints the following
> > forever:
> > insize is -1
> > black line //i think this is because inbuff is empty
>
> The read function _is_ blocking, but it times out after 10 seconds.
>
> > anyway i found that there is a function in skel_read function, named by
> > usb_bulk_msg and the last argument of it, is the timeout and if i set this
> > timeout to zero it will stop printing insize is -1 and thus it becomes a
> > blocking function.
>
> Because you removed the timeout.
>
> > so now if the gadget is not sending anything to the host, the while loop
> stops
> > printing
> > insize is -1
> > bu when the gadget really sends a word like "hello host" for example, the
> host
> > really receives it but still printing the phrase of insize is 64 i.e the
> output
> > is as follows:
> >
> > insize is 64
> > hello host
> > insize is 64
> > insize is 64 and it prints this phrase forever
> > so why it just receives 64B while i was really sending 2KB buffer?
>
> You are contradicting yourself. Above you said the gadget sends the words
> "hello host", which is 10 bytes, but now you say the gadget sends a
> 2048-byte buffer. Which is it?
on the gadget side i have a buffer of 2KB and i just fill 10 bytes of
it by "hello host" but i send all the buffer i.e i send 2KB. so can u
tell me now why the phrase of insize is 64 is repaeted forever while i
set the timeout to zero.i think it shall never appear as long as the
gadget is sending nothing and the read is blocking and the timeout is
zero?
thanks in advance
> > actually what i want exactly is when the gadget sends "hello host" the
> while
> > looop output is :
> >
> > insize is 2048 // 2KB=2048
> > hello host
>
> Why do you want your program to print that insize is 2048 when it received
> only 10 bytes from the gadget?
just u can skip this part now and neglect it please.
> Any funny behavior you encounter is probably caused by the gadget. If you
> know what it is really sending, then you should also know why the host
> behaves the way it does.
>
> > and doesnt print anything else?
> >
> > 2) can i make the following steps in reading instead of usb_bulk_msg:
> > 1.urb = usb_alloc_urb(0, GFP_KERNEL);
> > 2.buf = usb_buffer_alloc(dev->udev, writesize, GFP_KERNEL,
> &urb->transfer_dma);
>
> If buf is for reading, shouldn't you use readsize instead of writesize?
>
> > 3.copy_to_user(buf, user_buffer, readsize
> > 4.usb_fill_bulk_urb( urb, dev->udev,
> > usb_rcvctrlpipe(dev->udev, dev->bulk_in_endpointAddr),
> > buf, readsize, skel_read_bulk_callback, dev);
> > 5.urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
> > 6.usb_submit_urb
> >
> > the location of copy_to_user is correct?or it should be put after
> > usb_submit_urb?
>
> It definitely should go after usb_submit_urb. In fact, it shouldn't
> execute until after the URB has completed. Otherwise the data you hand
> back to the user won't be the data coming from the gadget; it will be
> whatever old data was sitting in buf.
>
> > this is the same algorithm for skel_write.so can i make the same algorithm
> with
> > skel_read?or not?
>
> Of course not. Reads are different from writes. A write takes data from
> the user and then sends it to the device. A read takes data from the
> device and then sends it to the user.
>
> Alan Stern
>
>
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