Hullo,
I'm a newbie in kernel development. I'm developing both the host-side
and the gadget-side of a usb connection, and i'm trying to setup an
isochronous transfer from the gadget to the host. My application needs
to allow the gadget to start sending a continuous flow of data
whenever it wants, thus the host has to wait until data are sent from
the gadget, and only then it can do its work.
So, I tryed two scenarios:
- first, i submitted the urb on the host-side as soon as possible,
while the gadget submitted isoc urbs only when data were available. In
this case, the host-side isoc-read callback was executed immediately
(i.e. the urb seems to complete) but no data was sent (actual_length =
0). Both the urb->status and the urb->iso_frame_desc[0].status were
always zero. When I started sending data from the gadget, no changes
happened to the host, even though I noticed that some sporadic buffer
has been received (one or two times);
- as the second scenario, I'm trying to let the gadget to start
sending packets first, while the host waits a little time to start
receiving. As a consequence, the first two or three buffers are
correctly received by the host, but then no more data is received
(i.e. actual_length = 0 and status = 0).
I use:
- a kernel 2.6.31.12 with the RT patch on the host;
- a a kernel 2.6.32-psp on the gadget (i.e. a beagleboard with a
OMAP3550 core). I used openembedded/bitbake to build the kernel for
the gadget system.
I use the following code to initialize the urb (host-side):
urb->dev = usb->udev;
urb->context = dev;
urb->pipe = usb_rcvisocpipe(usb->udev, iso_in->iso_in_endpointAddr);
urb->interval = 6;
urb->transfer_flags = URB_ISO_ASAP;
urb->transfer_buffer = iso_in->iso_in_buffer;
urb->complete = thmx_read_iso_callback;
urb->number_of_packets = NUM_ISO_PACKETS;
urb->transfer_buffer_length = iso_in->iso_in_size;
for (i=0; i < NUM_ISO_PACKETS; i++) {
urb->iso_frame_desc[i].offset = i;
urb->iso_frame_desc[i].length = iso_in->iso_in_size;
}
(NUM_ISO_PACKETS is 1). The callback is quite simple:
status = urb->iso_frame_desc[0].status;
if (status &&
!(status == -ENOENT ||
status == -ECONNRESET ||
status == -ESHUTDOWN)) {
dbg("%s - nonzero read isoc status received: %d",
__FUNCTION__, status);
return;
}
buf = urb->transfer_buffer;
actual_length = urb->iso_frame_desc[0].actual_length;
if (actual_length > 0) {
/* wake_up_worker_thread() */
}
retval = usb_submit_urb(urb, GFP_KERNEL);
if (retval) {
err("%s - failed submitting isoc read urb, error %d",
__FUNCTION__, retval);
}
on the gadget, i initialized the usb_endpoint_descriptor struct as follows:
static struct usb_endpoint_descriptor
hs_iso_in_desc = {
.bLength = USB_DT_ENDPOINT_SIZE,
.bDescriptorType = USB_DT_ENDPOINT,
.bmAttributes = USB_ENDPOINT_SYNC_NONE | USB_ENDPOINT_XFER_ISOC,
.wMaxPacketSize = cpu_to_le16(512),
.bInterval = 6,
};
I suspect that it should be a synchronization issue. I also tryed to
change the USB_ENDPOINT_SYNC_* attribute using SYNC_SYNC but without
luck... Could someone help me?
Thanks in advance,
Daniele
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