Achronix Speedster22i 10G/40G/100G Ethernet - Manual (Page 46)

46 UG029, September 6, 2013
Table 24 – Pause Frame Format (values in hex)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
55 55 55 55 55 55 55 D5 01 80 C2 00 00 01
Preamble SFD Multicast Destination Address
15 16 17 18 19 20 21 22 23 24 25 26 27 - 68
00 00 00 00 00 00 88 08 00 01 hi lo 00
Source Address Type Opcode Quanta pad (42)
69 70 71 72
xx xx xx xx
CRC-32
There is no Payload Length field found within a Pause Frame and a Pause Frame is always
padded with 42 bytes (0x00).
If a pause frame with a pause value greater than zero (XOFF Condition) is received, the MAC
stops transmitting data as soon as the current Frame transfer is completed. The MAC stops
transmitting data for the value defined in pause quanta. One pause quanta fraction refers to
512 bit times.
If a pause frame with a pause value of zero (XON Condition) is received, the transmitter is
allowed to send data immediately.
Priority Flow Control (PFC) Frames
The PFC frames have the following format:
Table 25 – PFC Frame Format (values in hex)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
55 55 55 55 55 55 55 D5 01 80 C2 00 00 01
Preamble SFD Multicast Destination Address
15 16 17 18 19 20 21 22 23 24 25 26 27 28
00 00 00 00 00 00 88 08 01 01 00 00-FF 0000-FFFF
Source Address Type Opcode Class Ena Quanta 0
29 30 31 32 33 34 35 36 37 38 39 40 41 42
0000-FFFF 0000-FFFF 0000-FFFF 0000-FFFF 0000-FFFF 0000-FFFF 0000-FFFF
Quanta 1 Quanta 2 Quanta 3 Quanta 4 Quanta 5 Quanta 6 Quanta 7
43 - 68 69 70 71 72
00 xx xx xx xx
Pad (26) CRC-32
The PFC frames use the same Length/Type field as Pause frames (0x8808). The Opcode field
0x0101 specifies the PFC frame. The 8 Class Enable bits define for each of the 8 priority
classes which class is currently enabled in the PFC frame. For each enabled priority class, a
16-bit Pause Quanta value is provided following the Class Enable field.