Confused about USB HID devices

[Peter Laursen]

Hi everyone,

I am trying to write a device driver for a USB HID device. The device in
question is a Braille display (electronic equipment that transforms
letters into braille dots for blind people to read). Potentially, this
driver may be the stepping stone for expanding our installer so that blind
people may be able to install FreeBSD without sighted assistance.

My problem is that, seemingly no matter what I do, I cannot get my braille
display to show any output if I go through my device driver. If I send
output from a test program written with the aid of libusb, the display
shows everything correctly, but when I send the same data from my test
device driver, I get an error code of 22.

When I send the following data packet from my libusb program, I see the
word "Hello":
(Every value is in decimal. The first three bytes is HID output report
byte for this device, next byte is offset on the display and the third is
the length of the data to be shown on the display)
"2 0 40 83 17 7 7 21 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0"

When I try to send the same data packet from within my device driver, I
get an error code with the value 22. I insert my USB callback function
below:
static void alva_write_callback(struct usb_xfer* xfer, usb_error_t err) {
struct alva_softc* sc = usbd_xfer_softc(xfer);
struct usb_device_request req;
req.bmRequestType = UT_WRITE_CLASS_INTERFACE;
req.bRequest=UR_SET_REPORT;
USETW2(req.wValue, UHID_OUTPUT_REPORT, 2);
req.wIndex[0]=1;
req.wIndex[1]=0;
USETW(req.wLength, 43);
mtx_lock(&sc->mtx);
switch (USB_GET_STATE(xfer)) {
case USB_ST_SETUP:
printf("Inside USB write setup state.\n");
usbd_xfer_set_frame_data(xfer,0,&req,8);
unsigned char Packet[43] = {0};
Packet[0]=2;
Packet[1]=0;
Packet[2]=40;
Packet[3] = 83;
Packet[4] = 17;
Packet[5] = 7;
Packet[6] = 7;
Packet[8] = 21;
for (int i = 9; i < 43; i++) Packet[i]=0;
usbd_xfer_set_frame_data(xfer,1,Packet,43);

usbd_transfer_submit(xfer);
break;
case USB_ST_TRANSFERRED:
printf("Reached the transferred state.\n");

break;

default:
printf("An error must have occurred. Error code: %d\n", err);
usbd_transfer_clear_stall(xfer);
break;

}
mtx_unlock(&sc->mtx);

}
I am quite out of ideas as to how I might solve the problem. I will gladly
provide any additional information, but I'm quite new to writing device
drivers, so please bear with me if I have missed anything obvious or
missed out important information.

I have looked through the USB HID driver,read the HID specification and
googled and nothing has given me any clues. I hope someone out here can
help guide me in the right direction.

All the best,

Peter.
FreeBSD 8.2-i386