jitter of I/O signals in the order of 1ns (or better)
a few LEDs
one-Wire EEPROM (such as DS28EC20P)
one-wire ROM temperature sensor with serial number (such as DS18B20U+)
A timing receiver must provide a dedicated serial console for the WR-PTP GUI for debugging. In case this is not provided by the carrier board, a serial console:USB port with USB to UART bridge (such as CP2101) is required on the add-n board.
A timing receiver must provide a serial interface for Etherbone, independently of the connection to the White Rabbit network. in case the form factor carrier board does not provide a host bus interface, a serial interface must be implemented by the add-on board (such as CY7C68013A-56BAXC).