Back Off Test Register (Bofftest); Transmit Pacing Algorithm Test Register (Tpacetest); Back Off Random Number Generator Test Register (Bofftest); Back Off Test Register (Bofftest) Field Descriptions - Texas Instruments TMS320DM646x User Manual

Ethernet Media Access Controller (EMAC) Registers

5.39 Back Off Test Register (BOFFTEST)

The back off test register (BOFFTEST) is shown in
Figure 79. Back Off Random Number Generator Test Register (BOFFTEST)
31
Reserved
R-0
15 12
COLLCOUNT
R-0
LEGEND: R = Read only; -n = value after reset
Bit Field
31-26 Reserved
25-16 RNDNUM
15-12 COLLCOUNT
11-10 Reserved
9-0 TXBACKOFF

5.40 Transmit Pacing Algorithm Test Register (TPACETEST)

The transmit pacing algorithm test register (TPACETEST) is shown in
Table 79.
Figure 80. Transmit Pacing Algorithm Test Register (TPACETEST)
31
15
LEGEND: R = Read only; -n = value after reset
Table 79. Transmit Pacing Algorithm Test Register (TPACETEST) Field Descriptions
Bit Field Value
31-5 Reserved 0
4-0 PACEVAL 0-1Fh
118 Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO)
26 25
11 10 9
Reserved
R-0
Table 78. Back Off Test Register (BOFFTEST) Field Descriptions
Value Description
0 Reserved
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.
0-Fh Collision count. These bits indicate the number of collisions the current frame has experienced.
0 Reserved
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.
Reserved
R-0
Description
Reserved
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.
Figure 79 and described in
RNDNUM
R-0
TXBACKOFF
R-0
Reserved
R-0
5
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Table 78.
Figure 80 and described in
4
PACEVAL
R-0
SPRUEQ6 – December 2007
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