Texas Instruments | AN-1287 DP83815 MacPHYTER and DP83816 MacPHYTER-II High Data Rate Stress Testing | Application notes | Texas Instruments AN-1287 DP83815 MacPHYTER and DP83816 MacPHYTER-II High Data Rate Stress Testing Application notes

Texas Instruments AN-1287 DP83815 MacPHYTER and DP83816 MacPHYTER-II High Data Rate Stress Testing Application notes
DP83815,DP83816
AN-1287 DP83815 MacPHYTER and DP83816 MacPHYTER-II High Data Rate Stress
Testing
Literature Number: SNLA057
National Semiconductor
Application Note 1287
June 2003
1.0
Client Mode
The client system is responsible for controlling the test and
sending test packets. At the same time, the client system
keeps track of the number and type of packets sent to each
of the servers participating in the test.
Scope

National Semiconductor performs extensive stress testing
on its 10/100 Mb/s Ethernet products. These tests include
the Microsoft Windows Hardware Quality Labs (WHQL)
Hardware Compatibility Test (HCT) for Network LAN
devices to ensure proper operation with Microsoft
WindowsTM operating systems.
The HCT test has revealed a receive packet corruption
scenario. Although this scenario has not been reproduced
under other high data rate stress tests, or actual network
conditions, in theory, this could result in a failure event in
an application that involves high data rate transfers.
This Application Note describes this scenario, and recommends software workarounds that minimize any possible
effect on overall system operation.
The National Windows driver set already implements a
workaround, hence this document is for descriptive
purposes only.
2.0
Introduction
To ensure hardware compatibility with Microsoft operating
systems, Windows Hardware Quality Labs (WHQL)
produce and support Hardware Compatibility Test (HCT)
kits. The HCT kit includes documentation and tests that
hardware manufacturers can use to test products and
drivers for compatibility and inter-operability with Windows
operating systems, and to qualify drivers for digital signature by Microsoft.
National uses the Microsoft Windows XP HCT 10.0 kit to test
its DP83815 MacPHYTERTM and DP83816 MacPHYTER-IITM
10/100 Mb/s Ethernet controllers, and their drivers.
The event described in this document occurs during
Microsoft’s WinXP HCT 10.0 kit stress tests. A description
of one of these tests, the NDIS (Network Driver Interface
Specification) stress test, follows.
2.1
NDIS STRESS TEST
The NDIS stress test creates a significant amount of
network traffic by sending and receiving packets of various
sizes, types and content.
For NDIS testing, a typical configuration consists of a client
system and at least one server system. The client system
will contain the network device being tested, also referred
to as the test device.
After the registration phase, testing begins. The client
continuously sends packets to each registered server in
turn. This continues for either a given number of iterations
or a given number of packets. After the test is completed,
the client queries each server for its test statistics, displays
them on the screen, and logs them to a file. Finally, it sends
a packet to each server and directs it to quit the test.
Server Mode
The server system receives packets and provides the
appropriate response. Depending on the command in a
packet, a server responds by either sending the packet
back to the client system or by discarding it. In either case,
the server sets its counter to track the number of received
packets, the number of packets it responded to, and any
errors that occurred in the test.
Client and Server Mode
The client can also run as both a client system and a server
system. This means it can send packets to server systems
and return packets to itself or to other client systems.
After NDIS testing is complete, the client system directs the
server system(s) to quit the test. All of the script files used
for NDIS testing are executed on the client system. The
client system logs all tests. The server system does not
create log files.
3.0
Scenario Characteristics
When running the NDIS stress test on the DP83815 or the
DP83816, there is a short hardware timing window, which
can occur during packet reception, that causes the Mac
portion of the device to incorrectly update its internal
packet FIFO read register. This timing window can only
occur when an incoming packet is rejected. In practice, the
most common and likely packet rejection condition is a
receive FIFO overrun. In this case, the incoming packet is
discarded due to a lack of space in the receive FIFO.
National Semiconductor is a registered trademark of National Semiconductor Corporation.
MacPHYTER is a trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation
www.national.com
AN-1287
Stress testing can take place in one of three modes:
Once initialized, the client broadcasts to all server systems
in the test. Systems operating in server mode respond to
the client system, register with the client, reset statistics
counters, and indicate readiness to process test packets
from the client.
DP83815 MacPHYTERTM and DP83816 MacPHYTER - IITM High Data Rate Stress Testing
DP83815 MacPHYTERTM and
DP83816 MacPHYTER - IITM
High Data Rate Stress Testing
AN-1287
If this timing window occurs, the Mac portion of the device
has incorrect data in the packet currently being transferred
to a host receive buffer, although the status of the packet
indicates no error. Because the internal FIFO read register
is set incorrectly after this condition, the receive logic indicates that there is another packet with a length greater
than the size of the receive packet FIFO that is ready for
transfer to the host.
receive descriptor architecture that allows packets to be
fragmented over two or more receive descriptors.
5.1
The Mac portion of the device then transfers this invalid
large packet to the host memory buffers. A common host
receive buffer layout is to allocate a maximum packet size
buffer to each receive descriptor. Because the packet is
larger than this, it is scattered across multiple receive
descriptors and the MORE bit in the COMMAND/STATUS
(cmdsts) field is set in the first descriptor. The MORE bit
may also be set in other descriptors, depending on the size
of the buffer assigned to each receive descriptor.
The driver’s receive-processing logic checks each packet
to determine the status of the MORE bit. If this bit is set, the
driver assumes that the previous packet contains invalid
data. Future packets are also affected until the receiver is
reset. When the error is detected, the driver discards the
previous receive packet, and all other packets indicated in
the receive descriptor list, and reclaims the buffers. It then
resets the Mac receiver (CR:RXR, register offset 00h), reinitializes the receive descriptor list, reprograms the RXDP
(register offset 30h) and RXCFG (register offset 34h), and
then enables the receiver (CR:RXE).
Because the internal FIFO read/write registers are out of
synchronization, future packets transferred to the host
might also be affected.
4.0
This solution might not detect and discard all invalid
packets. There is a short window where the corrupt packet
previous to a packet with the MORE bit set, straddles two
passes of the driver’s receive processing logic. In other
words, the driver processes a receive interrupt and
services the receive descriptor list. The last packet indicated on the receive descriptor list is corrupt. No subsequent packets have been indicated as complete by the
hardware. The driver processes the packets believing they
are valid, but the last one processed contains invalid data.
In the next receive interrupt, the first packet indicated has
the MORE bit set, indicating the failure event has occurred.
Because the driver has already processed the previous
invalid packet, and has no method to abort it, the upper
layer protocols attempt to process that invalid packet.
System Impact
The impact of this problem depends on the requirements
and assumptions made by higher layer protocol stacks. In
most TCP/IP based environments, this problem should
have little, if any, negative effects because TCP/IP discards
any corrupt packet that fails checksum verification.
If the device’s receive logic is consistently unable to keep
up with the incoming packet flow, and overruns occur
frequently, TCP closes its packet window down to a point
where overruns do not occur. Since this occurs in an
overrun case, regardless of whether packets were corrupt
or not, the failure scenario should not have a negative
impact on performance.
Applications that do not use TCP/IP may, or may not, be
affected by this problem. If the driver takes corrective
action, as outlined below, there may be no significant
impact to the system. If the driver does not correct for this
issue, and an upper layer transport does not validate the
packet with some sort of CRC or checksum, data corruption may occur. This may result in BSOD (Blue Screen Of
Death), system freeze, system shutdown or receive data
corruption.
5.0
5.2
FRAGMENTED RECEIVE BUFFERS
This method has not been validated. It is presented here as
a potential workaround for drivers that use fragmented
receive buffers. The method is basically the same as the
previous one, but uses the reported packet length to detect
the failure, instead of the MORE bit.
For a failure event, the sum of the SIZE fields in the receive
packet descriptors exceeds the maximum possible packet
size. The failure condition is thus detected, and is
corrected using the method described above.
Resolutions/Workarounds
Since this scenario is not expected to occur in real network
environments, no additional workaround is required for
general applications.
6.0
Summary
An anomaly has been observed on the DP83815
MacPHYTER and DP83816 MacPHYTER - II 10/100 Mb/s
ethernet controllers, during Microsoft WHQL WinXP HCT
10.0 stress tests. While in theory this condition can occur in
any high data rate stress test, it has only been observed in
Microsoft’s WHQL HCT environment.
If required, there are two approaches that the host driver
can use to detect and work around this failure.
• Full-Size Receive Buffers
This is appropriate when the host driver assigns a single
full-size (max Ethernet packet) buffer to each receive
descriptor. This approach is implemented in National’s
Windows driver set.
The symptoms are corruption of the frame buffer(s) during
packet receives, due to a rare intermittent hardware timing
window.
• Fragmented Receive Buffers
This approach can be used when the host driver uses a
www.national.com
FULL-SIZE RECEIVE BUFFERS
For full-size buffers (buffers that hold a full packet), packets are
not fragmented across the buffers. Consequently, each packet
has only one descriptor which means that the MORE status bit,
of the descriptor, is always zero. Thus, for a receive packet, the
driver can use the MORE bit to detect a failure event.
2
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AN-1287
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DP83815 MacPHYTERTM and DP83816 MacPHYTER - IITM High Data Rate Stress Testing
As a workaround, this failure condition can be detected
through software as described in Section 5.0, in two ways
depending on whether full size or fragmented buffers are
used. Once it has been detected the corrupted packets can
be discarded and the reception of valid packets can be
resumed.
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