SNLS504G October 2015 – June 2026 DP83867CS , DP83867E , DP83867IS
PRODUCTION DATA
When Full-Duplex operation is selected during priority resolution, the Auto-Negotiation also determines the Flow Control capabilities of the two link partners. Flow control is originally introduced to force a Link Partner of a busy station to stop transmitting data in Full-Duplex operation. Unlike the Half-Duplex mode of operation, where a link partner can be forced to back off by simply generating collisions, the Full-Duplex operation needed a mechanism to slow down transmission from a link partner in the event that the buffers of the receiving station become full. A new MAC control layer is added to handle the generation and reception of Pause Frames. Each MAC Controller has to advertise whether the controller can process Pause Frames. In addition, the MAC Controller advertises if Pause frames are handled in both directions, that is, receive and transmit. If the MAC Controller only generates Pause frames but does not respond to Pause frames generated by a link partner, the event is called Asymmetrical Pause. The advertisement of Pause and Asymmetrical Pause capabilities is enabled by writing 1 to bits 10 and 11 of ANAR (register address 0x0004). The Pause capabilities of the link partner is stored in ANLPAR (register address 0x0005) bits 10 and 11. The MAC Controller has to read from ANLPAR to determine which Pause mode to operate. The PHY layer is not involved in Pause resolution other than simply advertising and reporting of Pause capabilities.