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Keysight Technologies
Low-Cost DDR3 Decode and Analysis with
the 16850 Series Portable Logic Analyzers
Application Note
Introduction
As embedded systems take on more sophisticated applications,
they also require advanced external memory systems, such as
DDR3, in order to offer adequate throughput. At times it can be
helpful to see memory activity and perform some level of memory
analysis in order to properly validate and debug a prototype
system. New options now allow this at inexpensive price points
compared to previous solutions. New general-purpose, low-cost
logic analyzers, like the 16850 Series shown in Figure 1, offer the
performance required for such measurements as well as related
analysis tools to provide this kind of insight.
To support the goal of reducing the cost of these measurements, the DDR3 decoder
in the solution has been modified to work from address and command signals only,
thus reducing the total channel count necessary for meaningful measurements. For
example, an entry-level 34-channel system can perform DDR3 1333 address and
command state (synchronous) measurements and analysis for around $36K. In the
past, a logic analyzer solution that could offer these measurements and analysis
required a budget of around $100K.
This application note will outline how to make low-cost measurements on DDR3
interfaces and conduct performance analysis and compliance tests to evaluate
these memory systems during debug and validation of a digital prototype.
Probing requirements for DDR3 measurements
In order to make real-time measurements on the interface between the DDR3
memory controller and memory devices, it is necessary to probe signals in a way
that eliminates significant distortion and instead provides an accurate picture of
those signals. A good probing option for designs with embedded memories is a BGA
probe, as shown in Figure 2. Address, command, and data signals are intercepted
and brought by coaxial ribbon cable to the logic analyzer. DDR3 BGA interposers
contain a buried tip resistor to isolate the DRAM system from the logic analyzer
probing. This probing scheme is workable to DDR3 rates of up to 2400 Mbit per
second. This setup provides plenty of margin for the DDR3 1333 measurements
made by the 16850 Series.
Figure 2. x8 DDR3 BGA probe connection.
Other probing options include the use of either a DIMM interposer or a mid-bus
probe. Mid-bus probing involves placing connection pads or a connector somewhere
along the PC board memory traces between the IC containing the memory controller
and the memory ICs. A probe then touches those pads or it plugs into the connector
to get access to the DDR3 signals.
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The advantage of a BGA probe is that no special PC board modifications are
required other than ensuring there is enough keep out volume (kov) for the probe to
fit. In addition, logic analyzers come with setup files for various probes, such as the
Keysight Technologies, Inc. W3633A x8 DDR3 probe. The automated logic analyzer
setup can be seen in Figure 3. Only 34 logic analyzer channels are required for state
(synchronous) measurements, which can drive DDR3 memory analysis tools such as
performance analysis and compliance testing.
Figure 3. Logic analyzer automated state setup for x8 DDR3 BGA probe address and command lines.
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DDR3 bus decode from address and
command signals
One analysis tool that helps designers better understand how their external DDR3
memory is actually behaving is a memory decoder. This software takes raw acquired
address and command state signals and converts them into a more easily under-
stood format, as shown in Figure 4. Memory commands like "writes" and "reads"
are displayed along with related chip select, bank address, row address, and column
address information. Other commands like "activates" and "deselects" are shown.
This state-mode trace capture is stored in deep memory so it reflects a significant
amount of target activity time. The 16850 Series logic analyzers have a maximum
input clock frequency of 700 MHz, which allows the state capture of 667 MHz
address and command signals on DDR3 1333 memories.
Figure 4. Memory decoder trace of DDR3 address and command lines.
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Performance analysis
Although helpful, the typical deep-memory raw capture and related memory
decoder output provide more information than can be easily evaluated manually by
the logic analyzer user. But the DDR performance tool provides useful analysis by
taking all the captured and decoded information and processing it into a variety of
performance-oriented views. This valuable tool is one of four that are part of the
B4622B protocol compliance and analysis toolset.
Now the specific steps are outlined to use the toolset:
From "Tools," "External Applications," select the "DDR Performance Tool," as shown in
Figure 5.
Figure 5. Launch of the DDR performance tool.
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The configuration is using the DDR bus module called W3633A, the name of
Keysight's DDR3 BGA probe used in this measurement.
Click "OK," as shown in Figure 6.
Figure 6. Select DDR bus module "DDR3W3633A," and press "OK".
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Press the "Setup" tab, and note the settings from the configuration file shown in
Figure 7.
Figure 7. Setup for the DDR3 decoder.
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Press the "Run" tab, and press the "Run" button, as shown in Figure 8.
Figure 8. Choose default burst length equal to "8," use of the entire trace as the data range, and then
press "Run".
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Four examples of summary views from this first tool include the overview, refresh
statistics, address histogram, and effective data rate, as seen in Figures 9-12.
Figure 9. Performance tool analysis of command-type distribution.
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Figure 10. View of refresh cycle throughput.
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Figure 11. View of address space access distribution.
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Figure 12. DDR performance tool view of effective data rate.
Expected memory command distributions can be verified with the "distribution
view" of the performance analysis tool during particular modes of target operation.
It is easy to see if the target system is spending too much time in memory "dese-
lects," for example.
A prototype might be working functionally but lack overall system throughput. A
view of the read and write data rate can reveal a problem in the memory controller
design. The overall efficiency factor can also indicate an issue. Here a 51% effi-
ciency rate, although not necessarily bad, might not be adequate for the application.
When it comes to using memory address space, the memory controller typically
should spend very little time accessing a few memory locations and should spread
those memory accesses over a range. The histogram view of the accessed memory
space can reveal "hot spots" that can lead to premature memory failures.
Since the performance tool operates off of address and command signals, even
a 34-channel model 16850 Series logic analyzer is adequate for the task, thus
enabling a very low-cost option.
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Memory compliance testing
Another type of memory evaluation that can be helpful during prototype turn-on
is a test of compliance to the JEDEC specification. This evaluation can expose
errors within a memory controller design. Non-compliance to the spec can result in
data errors. A DDR post process compliance tool is available that also works from
address and command memory signals saved in logic analyzer memory. The type
of module is selected along with the type of memory being evaluated, its data rate,
and the desired tests. With this information, a suite of evaluation parameters can be
tested using the compliance tool.
Now the specific steps are outlined to perform compliance testing on the DDR3
memory system.
Launch the "DDR Post Process Compliance Tool" from "Tools," "External
Applications," as shown in Figure 13.
Figure 13. Launch the DDR post process compliance tool.
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Then press the "Select Tests" tab and select all the JEDEC spec tests, as shown in
Figure 14.
Figure 14. Select all memory compliance tests.
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Press the "Configure" tab, "Activate/Refresh Limit Set," and then select
"DDR3_1333_2K_U4154," as shown in Figure 15.
Figure 15. Select a limit set for the compliance tests of the DDR3 1333 memory.
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Press the "Run Tests" tab and then the "Run" button, as shown in Figure 16.
Figure 16. Select default settings to store details for the worst trials, and press "Run".
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The results of such a test can be seen in Figure 17 where failures were discovered
for the operation of four "activates" occurring from different banks of memory.
Figure 17. Memory compliance failure for four ACTIVATE windows (different banks) to be less than 45.0 ns.
By selecting the row that highlights an error, the interface displays the number
of discovered errors in the trace compared to the total number of that particular
operation that occurred in the trace. It also lists the first 25 exact state pairs associ-
ated with each error count in the deep memory trace. It is important not only to
report that errors occur but also the specific locations of those errors so that a root
cause of failure can be pursued. A real-time compliance tool also triggers the logic
analyzer on a violation.
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Timing-mode capture of address, command, and
memory read and write data
The measurements so far have all been state (synchronous) capture, but timing
(asynchronous) capture, including measurements on read and write data to track
memory data flow, can also be useful. For the DDR3 1333 memory system being
evaluated here, timing mode measurements require a timing sample rate that is fast
enough to determine bus activity. A 3-to-1 ratio of logic analyzer sample rate to tar-
get system data rate is a good guideline to follow. For the 1333 data rate, this would
translate to a 4 GHz or faster timing rate. The 16850 Series logic analyzers have a
half-channel, 5-GHz timing speed that meets this requirement. A half-channel timing
mode configuration is included with the analyzer for address, command, and data
capture. An example capture is shown in Figure 18.
A 102-channel model is necessary to provide 48 channels in the half-channel mode
so this measurement is able to capture address, command, and x8 or x16 data. Read
and write data is not separated in timing capture, but settled data bus read and
write values would still be seen in the DATA row with an expanded time/division
setting. If the state capture of separate read and write data is required, a modular
logic analyzer solution such as the U4154A offers a "dual sample mode" when in
state capture mode that can accomplish this.
Figure 18. 5-GHz timing mode capture of DDR3 1333 address, command, and data
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Positioning the 16850 Series portable logic analyzers with the modular
U4154A analyzers
Both 16850 Series portable logic analyzers and the modular U4154A analyzers offer 2.5-GHz full-channel and 5-GHz half-channel
timing measurements with deep memory. A comparison of timing and state mode capabilities is summarized in Figure 19 includ-
ing use of the B4621B DDR decoder and the B4622B protocol compliance and analysis toolset.
Measurements 16850 Series portable (34-, 68-, 102-, and U4154A modular (136 channels per module)
136-channel models)
Addr/Cmd state capture on DDR3 up to DDR3 Yes, up to DDR3 1333 (667 MHz clock, cmd, Yes, the U4154A can capture state data rates
1333 -- including DDR decoder, protocol addr, requires 34-channel model with option up to 4 Gb/s
compliance and analysis toolset 700 to increase max clock frequency to 700
MHz)
Addr/Cmd state capture on DDR3 over DDR3 No Yes, the U4154A can capture state data rates
1333 -- including DDR decoder, protocol up to 4 Gb/s
compliance and analysis toolset
Addr/Cmd/Data deep timing capture on DDR3 Yes, 5 GHz half channel* for up to DDR3 1600 Yes, 5 GHz half channel* for up to DDR3 1600,
(no DDR decoder, no compliance and analysis x8 or x16, up to 256M sample depth (requires up to 400M sample depth
toolset) 102-channel model)
Addr/Cmd/Data high-resolution "timing zoom" Yes, 12.5 GHz full channel (requires 68-chan- Yes, 12.5 GHz full channel
capture (simultaneous with normal state or nel model for x8 and x16 data width)
timing capture from one probe point), 256k
samples depth (no DDR decoder, no compli-
ance and analysis toolset)
Addr/Cmd/data state capture on DDR2/3/4 No (clock input limited to 700 MHz for state Yes, the U4154A can capture data rates up to
and LPDDR2/3/4 -- including DDR decoder, capture and cannot separate out DDR read 4 Gb/s
protocol compliance and analysis toolset and Writes for state capture and cannot de-
multiplex addr/cmd bus on LPDDR2/3) Standard DDR3 probing covers data capture
up to 2500 Mb/s. Data rates over 2500 require
specialty probing
As of Feb. 2014, DDR4 has been captured at
data rates up to DDR4 2400. DDR4 is expected
to achieve higher data rates in the future
* Timing mode guideline is sample rate >= 3x data rate. 5-GHz sample rate allows viable timing captures up to DDR 1600. Decoders and compliance toolset are designed for state mode captures only.
Table 1. Comparison of 16850 Series portable logic analyzer and U4154A modular logic analyzer timing and state capture capabilities
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State and timing measurement options and related probing requirements
for 16850 Series analyzers
The state analysis capabilities of the 16850 Series allow it to make measurements and analysis on DDR2 and DDR3 memories up to DDR2/3
1333 (667 MHz clock) on address and control lines. Memory bus decode, compliance testing, and performance analysis are available in
state mode only with related orderable tools. These options are outlined in Table 2. Timing analysis can be extended to memory data rates
of 1600 Mbps by using half-channel, 5-GHz timing mode, but 102 channels are required to capture addr/cmd/x8-x16 data.
DDR2 memory DDR3 memory
Addr/Cmd only Up to DDR2 1333 (667 MHz clock) state measurements on Up to DDR3 1333 (667 MHz clock) state measurements on
Addr/Cmd only. (No Data) Addr/Cmd only. (No Data)
Requires 34 channel model or higher (one U4201A cable required providing two 90 pin pods)
Related Orderable SW Tools (State mode only):
B4621B Bus Decoder for DDR, DDR2, DDR3, DDR4 Debug and Validation (Only DDR2 and DDR3 are supported with the
16850 Series logic analyzer.)
B4622B Protocol Compliance and Analysis Toolset for DDR/2/3/4, and LPDDR/2/3 (Only DDR2 and DDR3 are sup-
ported with the 16850 Series logic analyzer.)
Supported probes with configuration files: Supported probes with configuration files:
x16 Addr/Cmd/Data DDR2 BGA probe (W2631B)(Requires x16 Addr/Cmd/Data DDR3 BGA probe (W3631A)(Requires
E5384A ZIF probe) 1 E5845A ZIF probe) 1
x8 Addr/Cmd/Data DDR2 BGA probe (W2633B)(Requires x8 Addr/Cmd/Data DDR3 BGA probe (W3633A) (Requires
E5384A ZIF probe) 1 E5847A ZIF probe) 1
FS2372 DDR3 DIMM interposer (Addr/Cmd only)
FS2374 DDR3 SODIMM interposer (Addr/Cmd only)
Addr/Cmd/Data Up to DDR2 800 (400 MHz clock) timing measurements Up to DDR3 800 (400 MHz clock) timing measurements
using 2.5 GHz timing analyzer with deep memory (for 3:1 using 2.5 GHz timing analyzer with deep memory (for 3:1
ratio of sample rate to data rate) ratio of sample rate to data rate)
Requires 68 channel model or higher (two U4201A cables using three of the four 90 pin pods provided)
Supported probes with configuration files: Supported probes with configuration files:
x16 Addr/Cmd/Data DDR2 BGA probe (W2631B)(Requires x16 Addr/Cmd/Data DDR3 BGA probe (W3631A)(Requires
E5384A ZIF probe) E5845A ZIF probe)
x8 Addr/Cmd/Data DDR2 BGA probe (W2633B)(Requires x8 Addr/Cmd/Data DDR3 BGA probe (W3633A) (Requires
E5384A ZIF probe) E5847A ZIF probe)
For higher speed memory analysis or greater channel count refer to the U4154A logic analyzer module.
Data pod is not connected for state measurements when used with the 16850 Series. Simultaneous state mode capture of read and write data requires a U4154A high-performance logic analyzer
module with dual sample mode. The W3631A was designed to work with stacked DRAM under 2G bytes depth and brings out two CS and two ODT signals. An alternate probe, the W3636A, was
designed for non-stacked DRAM of any depth, and brings out one CS, one ODT signal, and BA2 and A15. Refer to the W3630A Series BGA probe data sheet (publication number 5990-3179EN) for
more details.
Table 2. Options for state and timing capture of DDR2/3 with the 16850 Series logic analyzers.
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Summary
It is now possible to capture DDR3 1333 address and command signals with a
low-cost, 34-channel general purpose portable logic analyzer in state (synchronous)
mode and conduct memory decode, performance analysis, and compliance testing
to help validate and debug digital designs. By using the 5-GHz half-channel timing
mode with a 102-channel analyzer, waveforms of DDR3 1600 address, command,
and x8 / x16 data signals from a DRAM can be viewed to help with overall system
evaluation. Memory depth can be as high as 256M samples. The 12.5-GHz "timing
zoom" timing capture can also be used for such measurements and only requires
a 68-channel model analyzer to do so, however memory depth is limited to 256k
samples. Although DDR decode of the DDR3 traffic is not supported in timing mode
and performance analysis and compliance testing is not available in this mode,
valuable debugging insight is provided by viewing the timing waveforms.
Modular analyzers (U4154A) are available for state capture on faster memories with
higher data rates (up to 4G bit per second), including DDR3/4 and LPDDR2/3/4
memories. They also provide the capture and separation of memory read and write
data and include DDR memory decode, performance analysis, and compliance
testing.
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23 | Keysight | Low-Cost DDR3 decode and Analysis with the 16850 Series Portable Logic Analyzers - Application Note
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