VSC7511 datasheet(34/324 Pages) MICROSEMI

34 / 324 page

Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

•

Backoff after excessive collision. Field MAC_HDX_CFG.WEXC_DIS determines whether the

MAC backs off after an excessive collision has occurred. If set, backoff is disabled after excessive

collisions.

•

Retransmission of frame after excessive collision. Field

MAC_HDX_CFG.RETRY_AFTER_EXC_COL_ENA determines whether the MAC retransmits

frames after an excessive collision has occurred. If set, a frame is not dropped after excessive

collisions, but the backoff sequence is restarted. This is a violation of IEEE 802.3, but is useful in

non-dropping half-duplex flow control operation.

•

Late collision timing. Field MAC_HDX_CFG.LATE_COL_POS adjusts the border between a

collision and a late collision in steps of 1 byte. According to IEEE 802.3, section 21.3, this border is

permitted to be on data byte 56 (counting frame data from 1); that is, a frame experiencing a collision

on data byte 55 is always retransmitted, but it is never retransmitted when the collision is on byte 57.

For each higher LATE_COL_POS value, the border is moved 1 byte higher.

•

Rx-to-Tx inter-frame gap. The sum of MAC_IFG_CFG.RX_IFG1 and MAC_IFG_CFG.RX_IFG2

establishes the time for the Rx-to-Tx inter-frame gap. RX_IFG1 is the first part of half-duplex Rx-to-

Tx inter-frame gap. Within RX_IFG1, this timing is restarted if carrier sense (CRS) has multiple high-

low transitions (due to noise). RX_IFG2 is the second part of half-duplex Rx-to-Tx inter-frame gap.

Within RX_IFG2, transitions on CRS are ignored.

When enabling a port for half-duplex mode, the switch core must also be enabled

(SYS::FRONT_PORT_MODE.HDX_MODE).

3.2.1.4

Frame and Type/Length Check

The MAC supports frame lengths of up to 16 kilobytes. The maximum length accepted by the MAC is

configurable in MAC_MACLEN_CFG.MAX_LEN.

The MAC allows tagged frames to be 4 bytes longer and double-tagged frames to be 8 bytes longer than

the specified maximum length (MAC_TAGS_CFG.VLAN_LEN_AWR_ENA). The MAC must be

configured to look for VLAN tags. By default, EtherType 0x8100 identifies a VLAN tag. In addition, a

custom EtherType can be configured in MAC_TAGS_CFG.TAG_ID. The MAC can be configured to look

for none, one, or two tags (MAC_TAG_CFG.VLAN_AWR_ENA,

MAC_TAG_CFG.VLAN_DBL_AWR_ENA).

The type/length check (MAC_ADV_CHK_CFG.LEN_DROP_ENA) causes the MAC to discard frames

with type/length errors (in-range and out-of-range errors).

3.2.1.5

Flow Control (IEEE 802.3x)

The device supports both standard full-duplex flow control (IEEE 802.3x) and priority-based flow control

(IEEE 802.1Qbb). This section describes standard full-duplex flow control, and Priority-Based Flow

Control (IEEE 802.1Qbb), page 20 describes priority-based flow control.

In full-duplex mode, the MAC provides independent support for transmission of pause frames and

reaction to incoming pause frames. This allows for asymmetric flow control configurations.

The MAC obeys received pause frames (MAC_FC_CFG.RX_FC_ENA) by pausing the egress traffic

according to the timer values specified in the pause frames. In order to evaluate the pause time in the

incoming pause frames, the link speed must be specified (SYS::MAC_FC_CFG.FC_LINK_SPEED).

The transmission of pause frames is triggered by assertion of a flow control condition in the ingress

queues caused by a queue filling exceeding a watermark. For more information, see Ingress Pause

Request Generation, page 126. The MAC handles the formatting and transmission of the pause frame.

The following configuration options are available:

•

Transmission of pause frames (MAC_CFG_CFG.TX_FC_ENA).

•

Pause timer value used in transmitted pause frames (MAC_FC_CFG.PAUSE_VAL_CFG).

•

Flow control cancellation when the ingress queues de-assert the flow control condition by

transmission of a pause frame with timer value 0 (MAC_FC_CFG.ZERO_PAUSE_ENA).

•

Source MAC address used in transmitted pause frames (MAC_FC_MAC_HIGH_CFG,

MAC_FC_MAC_LOW_CFG).

The MAC has the option to discard incoming frames when the remote link partner is not obeying the

pause frames transmitted by the MAC. The MAC discards an incoming frame if a Start-of-Frame is seen

after the pause frame was transmitted. It is configurable how long reaction time is given to the link partner

VSC7511 датащи(PDF) 34 Page - Microsemi Corporation

VSC7511 датащи(HTML) 34 Page - Microsemi Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL