ATHN_USB_HOST_CMD_RING_COUNT
ring->next = (ring->next + 1) % ATHN_USB_HOST_CMD_RING_COUNT;
if (ring->queued == ATHN_USB_HOST_CMD_RING_COUNT) {
ring->cur = (ring->cur + 1) % ATHN_USB_HOST_CMD_RING_COUNT;
struct athn_usb_host_cmd cmd[ATHN_USB_HOST_CMD_RING_COUNT];