This read-write enumeration — normalinternal(1), normalterminal(2), invertedinternal(3), or invertedterminal(4) — configures whether the HSSI interface's receive clock is sourced internally or from the terminal, and whether it is inverted; like its transmit counterpart, it only applies to the HSSI interface on the USSI card. It lets an admin correct receive-side clock phase problems independently of the transmit clock setting. For example, an admin seeing receive CRC errors might set hssiConfigRxClockSource to invertedinternal(3) to fix a phase mismatch.