
122
Functional Operation
Chapter 3
AMD-8111 HyperTransport I/O Hub Data Sheet
24674
Rev. 3.00
April 2003
AMD Preliminary Information
PAUSE frames. In an asymmetric configuration only one link partner transmits PAUSE frames and
the other one receives them. During the auto-negotiation process each link partner indicates its
configuration preference in the form of PAUSE and ASM_DIR bits that are sent in MII Management
Frames. The encoding of these bits is shown in Table 35.
During the auto-negotiation process the PHY device attached to the LAN Ethernet controller
controller exchanges configuration information with the PHY device on the other end of the network
link segment as described in IEEE standard 802.3, 1998 Edition, Clause 28. The value of the PAUSE
bit that is sent in MII Management frames is copied from the Negotiate Pause Ability bit (NPA,
FLOW_CONTROL Register, bit 19), and the value of the ASM_DIR bit is copied from the Negotiate
Asymmetric Pause Ability bit (NAPA, FLOW_CONTROL Register, bit 20).
After auto-negotiation has finished, receive pause is enabled if either
1. The NPA bit is set and link partner’s PAUSE bit is also set or
2. The NPA and NAPA bits are both set and the link partner’s ASM_DIR bit is set.
After auto-negotiation has finished, transmit pause is enabled if either
1. The NPA bit is set and link partner’s PAUSE bit is also set or
2. The NAPA bit is set and the link partner’s PAUSE and ASM_DIR bits are set.
3.10.14.7
PAUSE Frame Reception
A MAC Control PAUSE frame is any valid frame with the following:
A destination address field value equal to the MAC’s physical address or equal to the reserved
multicast address 01-80-C2-00-00-01,
A Length/Type field value equal to 88-08, and
A MAC Control Opcode field value equal to 0001.
If such a frame is received while pause ability is enabled, the MAC device waits until the end of the
frame currently being transmitted (if any) and then stops transmitting for a time equal to the value of
the request_operand field (octets 17 and 18) multiplied by 512-bit times.
If another MAC Control PAUSE frame is received before the Pause timer has timed out, the Pause
timer is reloaded from the request_operand field of the new frame so that the new frame overrides the
earlier one.
Table 35.
Pause Encoding
PAUSE
0
0
1
1
ASM_DIR
0
1
0
1
Capability
No PAUSE
Asymmetric PAUSE toward link partner
Symmetric PAUSE
Both Symmetric PAUSE and Asymmetric PAUSE toward local device