Ethernet Media Access Controller (EMAC)/ Management Data Input/Output (MDIO) Module User's Guide

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5.39 Back Off Test Register (BOFFTEST)
5.40 Transmit Pacing Algorithm Test Register (TPACETEST)
Ethernet Media Access Controller (EMAC) Registers
The back off test register (BOFFTEST) is shown in Figure 79 and described in Table 78 .
Figure 79. Back Off Random Number Generator Test Register (BOFFTEST)
31 26 25 16
Reserved RNDNUM
R-0 R-0
15 12 11 10 9 0
COLLCOUNT Reserved TXBACKOFF
R-0 R-0 R-0
LEGEND: R = Read only; - n = value after reset
Table 78. Back Off Test Register (BOFFTEST) Field Descriptions
Bit Field Value Description
31-26 Reserved 0 Reserved
25-16 RNDNUM 0-3FFh Backoff random number generator. This field allows the Backoff Random Number Generator to be
read. Reading this field returns the generator's current value. The value is reset to 0 and begins
counting on the clock after the deassertion of reset.
15-12 COLLCOUNT 0-Fh Collision count. These bits indicate the number of collisions the current frame has experienced.
11-10 Reserved 0 Reserved
9-0 TXBACKOFF 0-3FFh Backoff count. This field allows the current value of the backoff counter to be observed for test
purposes. This field is loaded automatically according to the backoff algorithm, and is decremented
by one for each slot time after the collision.
The transmit pacing algorithm test register (TPACETEST) is shown in Figure 80 and described in
Table 79 .
Figure 80. Transmit Pacing Algorithm Test Register (TPACETEST)
31 16
Reserved
R-0
15 5 4 0
Reserved PACEVAL
R-0 R-0
LEGEND: R = Read only; - n = value after reset
Table 79. Transmit Pacing Algorithm Test Register (TPACETEST) Field Descriptions
Bit Field Value Description
31-5 Reserved 0 Reserved
4-0 PACEVAL 0-1Fh Pacing register current value. A nonzero value in this field indicates that transmit pacing is active. A
transmit frame collision or deferral causes PACEVAL to be loaded with 1Fh (31); good frame
transmissions (with no collisions or deferrals) cause PACEVAL to be decremented down to 0. When
PACEVAL is nonzero, the transmitter delays four Inter Packet Gaps between new frame transmissions
after each successfully transmitted frame that had no deferrals or collisions. If a transmit frame is
deferred or suffers a collision, the IPG time is not stretched to four times the normal value. Transmit
pacing helps reduce capture effects, which improves overall network bandwidth.
Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO)118 SPRUEQ6 – December 2007
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