dp83901a National Semiconductor Corporation, dp83901a Datasheet - Page 36

• Manufacturer Part Number: dp83901a
• Description: Serial Network Interface Controller
• Manufacturer: National Semiconductor Corporation

12 0 Loopback Diagnostics
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 packer arrives In
situations where another packet arrives very quickly the
CPU may have no opportunity to do this The SNIC 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 counter 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 the
SNIC misses due to buffer overflow or being offline
The structure of the counters is shown below
(Continued)
TL F 10469 – 19
36
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
Errors CRC Errors
Frames Received OK
Multicast Frames Received
Packets Lost Due to Lack of Resources
Retries Packet
Alignment Errors
Excessive Collisions
Packet with Length Errors
Heartbeat Failure