Priority flow control (pfc) frames – Achronix Speedster22i 10G/40G/100G Ethernet User 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.