USB Transmit Packet Length
PKT_LNGTH | The remaining number of bytes to be written to the selected endpoint buffer. This field is decremented by 4 by hardware after each write to USBTxData. When this field decrements to 0, the TxENDPKT bit will be set in USBDevIntSt. |
RESERVED | Reserved, user software should not write ones to reserved bits. The value read from a reserved bit is not defined. |