DP8390D datasheet(32/56 Pages) NSC

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120 Loopback Diagnostics (Continued)

PATH

TCR

RCR

TSR

RSR

ISR

NIC External

43(1)

Note 1

CDH is set CRS is not set since it is generated by the external

encoderdecoder

PATH

TCR

RCR

TSR

RSR

ISR

NIC External

03(1)

02(2)

Note 1

CDH and CRS should not be set The TSR however could also

contain 01H03H07H and a variety of other values depending on whether

collisions were encountered or the packet was deferred

Note 2

Will contain 08H if packet is not transmittable

Note 3

During external loopback the NIC is now exposed to network traffic

it is therefore possible for the contents of both the Receive portion of the

FIFO and the RSR to be corrupted by any other packet on the network Thus

in a live network the contents of the FIFO and RSR should not be depended

on The NIC will still abide by the standard CSMACD protocol in external

loopback mode (ie The network will not be disturbed by the loopback

packet)

Note 4

All values are hex

CRC AND ADDRESS RECOGNITION

The next three tests exercise the address recognition logic

and CRC These tests should be performed using internal

loopback only so that the NIC is isolated from interference

from the network These tests also require the capability to

generate CRC in software

The address recognition logic cannot be directly tested The

CRC and FAE bits in the RSR are only set if the address of

the packet matches the address filters If errors are expect-

ed to be set and they are not set the packet has been

rejected on the basis of an address mismatch The following

sequence of packets will test the address recognition logic

The DCR should be set to 40H the TCR should be set to

03H with a software generated CRC

Packet Contents

Results

Test

Address

CRC

RSR

Test A

Matching

Good

01(1)

Test B

Matching

Bad

02(2)

Test C

Non-Matching

Bad

Note 1

Status will read 21H if multicast address used

Note 2

Status will read 22H if multicast address used

Note 3

In test A the RSR is set up In test B the address is found to match

since the CRC is flagged as bad Test C proves that the address recognition

logic can distinguish a bad address and does not notify the RSR of the bad

CRC The receiving CRC is proven to work in test A and test B

Note 4

All values are hex

NETWORK MANAGEMENT FUNCTIONS

Network management capabilities are required for mainte-

nance and planning of a local area network The NIC sup-

ports the minimum requirement for network management in

hardware the remaining requirements can be met with soft-

ware counts There are three events that software alone

can not track during reception of packets CRC errors

Frame Alignment errors and missed packets

Since errored packets can be rejected the status associat-

ed with these packets is lost unless the CPU can access the

Receive Status Register before the next packet arrives In

situations where another packet arrives very quickly the

CPU may have no opportunity to do this The NIC counts

the number of packets with CRC errors and Frame Align-

ment errors 8-bit counters have been selected to reduce

overhead The counters will generate interrupts whenever

their MSBs are set so that a software routine can accumu-

late the network statistics and reset the counters before

overflow occurs The counters are sticky so that when they

reach a count of 192 (C0H) counting is halted An additional

counter is provided to count the number of packets NIC

misses due to buffer overflow or being offline

The structure of the counters is shown below

TLF8582 – 63

Additional information required for network management is

available in the Receive and Transmit Status Registers

Transmit status is available after each transmission for infor-

mation regarding events during transmission

Typically the following statistics might be gathered in soft-

ware

Traffic

Frames Sent OK

Frames Received OK

Multicast Frames Received

Packets Lost Due to Lack of Resources

RetriesPacket

Errors

CRC Errors

Alignment Errors

Excessive Collisions

Packet with Length Errors

Heartbeat Failure

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