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. Read value is undefined, only zero should be written. |