PMC-1980495

The standard FIFO depth for POS-PHY interfaces is 256 octets. The transmit buffer PMC-1980495 shall have a programmable threshold defined in terms of the number of bytes available in the FIFO for the assertion and deassertion of the transmit packet available flags.

In this fashion, transmit latency can be managed, and advance TPA lookahead can be achieved. PMC-1980495 will allow a Link Layer device to continue to burst data in, without overflowing the transmit buffer, after TPA has been deasserted.

In the transmit direction, the PHY layer device PMC-1980495 shall not initiate data transmission before a predefined number of bytes or an end of packet flag has been stored in the transmit FIFO. This capability of PMC-1980495 does not affect the POS-PHY bus protocol, but is required to avoid transmit FIFO underflow and frequent data retransmission by the higher layers.