HID_OUTPUT_FIFO_SIZE
if (n >= HID_OUTPUT_FIFO_SIZE / 2) {
usbhid->outtail = (usbhid->outtail + 1) & (HID_OUTPUT_FIFO_SIZE - 1);
if ((head = (usbhid->outhead + 1) & (HID_OUTPUT_FIFO_SIZE - 1)) == usbhid->outtail) {