USBD_TXFIFO_CONFIG_START_SHIFT
#define USBD_TXFIFO_CONFIG_START_MASK (0xff << USBD_TXFIFO_CONFIG_START_SHIFT)
#define USBD_RXFIFO_CONFIG_START_MASK (0xff << USBD_TXFIFO_CONFIG_START_SHIFT)
val = (tx_fifo_slot << USBD_TXFIFO_CONFIG_START_SHIFT) |