VT6516 datasheet(61/73 Pages) ETC

61 / 73 page

VIA Technologies, Inc.

Preliminary VT6516 Datarsheet

-61-

02H

Backoff configuration

bit 0: CAP mode , mild solution for Capture effect

bit 1: MBA mode , aggressive solution for Capture

effect

bit 2: EEFAST mode , drop the 2

nd collided packet

for testing

purpose, accelerate the drop event

bit 3: CRANDOM mode , use another random

algorithm

bit 4: OFSET , parameter for backoff timer

For that CAP mode is enabled, the TMAC module

will select the backoff time as b’10 or b’11 for the

nd collision, i.e. the backoff time for the 2nd collision

is 2 or 3 slot times, where a slot time is 512 bits time

duration.

For that MBA mode is enabled, the TMAC will

select

backoff time for 10

th collision just as that for 5th

collision

backoff time for 11

th collision just as that for 4th

collision

backoff time for 12

th collision just as that for 3rd

collision

backoff time for 13

th collision just as that for 2nd

collision

backoff time for 14

th collision just as that for 1st

collision

backoff time for 15

th collision as 0.

For that EEFAST mode is enabled, the Output

Control will drop the packet immediately as the

second collision happens.

For that CRANDOM mode is enabled, the TMAC

will select the backoff time by using the alternative

random algorithm that calculates the backoff time as

that for 10

th collision.

For OFSET=1, the TMAC will follow the 802.3

standard backoff algorithm. For OFSET=0, the

TMAC will select the backoff time for the 1

st and 2nd

collision as that of the 3

rd collision, i.e. the possible

the backoff time for the 1

st and 2nd collision is ranged

from 0 to 7 in unit of slot time.

BOFFCFG [4:0] 5’b10

000

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