DP83840AVCE datasheet(68/91 Pages) TI1

68 / 91 page

National Semiconductor

Version A

7.0 Software User Information

7.1 100 Mb/s Full Duplex Log-On

Problem:

Certain Software drivers that were developed for the

DP83840 do not account for the longer auto-negotiation

time that is required for the DP83840A to complete Auto-

Negotiation. This is discussed in the IEEE speciﬁcation

802.3U from draft D2 to D5. The Auto-Negotiate time has

increased from 1 second to approximately 3 seconds

between the two devices.

Description:

The problem can be seen when the server or the client

physical layer device is the DP83840A. When the client is

attempting to log on to the server the user will see CRC

errors occurring until the client times out and disconnects.

The driver software that was written for the DP83840

needs to be modiﬁed to account for the additional time per

the speciﬁcation 802.3(D5.3) that is required for the

DP83840A to complete Auto-Negotiation.

Symptoms:

A Novell server and a Novell DOS client that are connected

via a crossover cable will not log on to 100 Mb/s Full

Duplex with the DP83840A in the client or the server.

Solution/Workaround:

The

solution

modify

the

driver

software

accommodate the longer Auto-Negotiation time that is

required. The basic script should be the following:

A.) Wait for auto-negotiation to complete (Three seconds)

B.) Verify whether the auto-negotiation is completed by

reading BSMR bit<5>.

C.) If BMSR<5> is set read the BMSR to update the link

status BMSR<2>.

D.) If the BMSR<2> is set, read the PAR (19h) register.

PAR bits<7:6> reﬂect the Duplex_STAT and Speed_10

status.

7.2 Auto-Negotiation to Link Sending 100 Mb/s

Scrambled Idles.

Problem:

The DP83840A when Auto-Negotiating with a 100 Mb/s

link partner that is sending out 100 Mb/s scrambled idles

can, for speciﬁc cable lengths, approximately 35 to 41

meters or equivalent attenuation, misinterpret the 100 Mb/s

scrambled idles as FLP’s (Fast Link Pulses), thereby

causing a false MLF (Multiple Link Fault) condition which

hangs the Auto-Negotiation process (No link established).

This problem only occurs with the above scenario and

does not affect other methods of linking such as Auto-

Negotiating to a 10 Mb/s link partner, Auto-Negotiating to a

Auto-Negotiation link partner, forcing the DP83840A into

100 Mb/s mode and linking to a 100 Mb/s link partner, and

forcing the DP83840A into 10 Mb/s mode and linking to a

10 Mb/s link partner.

Description:

When Scrambled 100 Mb/s idles are transmitted, the

energy is dispersed across the spectrum from 1MHz to

31.25 MHz. Some of this energy is aliased in the 10 Mb/s

domain and for speciﬁc cable lengths, between 35meters

to 41meters or equivalent attenuation, is falsely detected

as FLP pulses. At these speciﬁc cable lengths, the Auto-

Negotiation receive state machine will misconstrue enough

FLP pulses such that it ﬁts the FLP template, thereby

notifying the arbitration state machine of the receipt of FLP

pulses.

At the same time the misconstrued FLP’s are being

detected, the arbitration state machine is moving through

the parallel detection path. This causes the arbitration state

machine to think that it is receiving both FLP pulses and

100 Mb/s scrambled idles, thereby, causing a parallel

detection fault (MLF bit 4 set high in the Auto-Negotiation

expansion

(06h)),

and

hanging

the

Auto-

Negotiation process.

Symptoms:

This problem only occurs when a system using the

DP83840A is in Auto-Negotiation mode and tries to

establish link with a system that is sending out 100 Mb/s

scrambled idles and the cable length is approximately

35meters to 41 meters or equivalent attenuation. When the

problem occurs the following will be observed:

A.) Pin 38 (Link LED) will go low indicating 100 Mb/s

activity.

B.) The Multiple Link Fault bit (bit 4) of the Auto-

Negotiation Expansion Register (06h) is HIGH, indicating

the DP83840A thinks FLP’s were being received.

C.) The Link Status bit (bit 2) of the Basic Mode Status

D.) The Auto-Negotiation Complete bit (bit 3) in the Basic

Mode Status Register (01h) is LOW, indicating Auto-

Negotiation not complete.

Solution/Workaround:

For existing products using the DP83840A the following

can be done to work around the problem:

A.) Manually conﬁgure the system using the DP83840A

into 100 Mb/s mode through software. Many installation

programs already support this capability.

B.) Modify software driver to detect fault condition. A

proposed software driver work around for this problem

follows:

The workaround is based upon the concept that a

DP83840A that is failing to complete negotiation is

attempting to negotiate with a non-Auto-Negotiation-

capable 100 Mb/s link partner. In that case, the software

driver can force the local node/port directly into 100 Mb/s

Half-Duplex mode to complete negotiation. Half-Duplex

100 Mb/s mode is what the Auto-Negotiation logic would

select had the fault not occurred. The total time that Auto-

Negotiation will take to complete is under 3 seconds.

Therefore, the proposed software driver should implement

the following:

Reset the 840A the DP83840A by writing 8000h to BMCR

BMCR register. Wait 3 seconds then read bit 5 (Auto-

Negotiation Complete bit) and bit 2 (Link_Status bit) in the

DP83840AVCE Datasheet(PDF) 68 Page - Texas Instruments

DP83840AVCE Datasheet(HTML) 68 Page - Texas Instruments

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