Priority-Based Flow Control Frames - 9.0 English

Tri-Mode Ethernet MAC LogiCORE IP Product Guide (PG051)

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Priority-based flow control frames are a special type of Ethernet frame defined in IEEE 802.1Qbb. Control frames are identified from other frame types by a defined value placed into the length/type field (the MAC Control Type code). The priority-based flow control frame format is shown in the following figure.

Figure 1. MAC Priority Control Flow Frame Format

A PFC frame is a special type of control frame identified by a defined value placed into the OPCODE field. This is shown in the previous figure.

The 16-bit priority enable vector contains eight priority enable bits with all other bits set to zero. The priority vector field contains eight 16-bit quanta values, one for each priority, with priority 0 being the first. This defines the number of pause_quantum (512-bit times of the particular implementation) for the priority pause duration request. For 10 Gb Ethernet, a single pause_quantum corresponds to 51.2 ns.