USB_MTU
frame_size = (USB_MTU / sub_size) * sub_size;
memmove(mbo->virt_address + j * USB_MTU,
mbo->buffer_length = num_frames * USB_MTU;
num_frames = mbo->processed_length / USB_MTU;
mbo->virt_address + USB_MTU * j,
if (frame_size == 0 || frame_size > USB_MTU) {
conf->extra_len = num_frames * (USB_MTU - frame_size);