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Use the Xilinx ChipScope Pro integrated logic analyzer for FPGAs
as a board- and system-level diagnostic tool.
Your FPGA designs have become increasingly
dense and complex. They are difficult
to debug because more and more of
the relevant signals are buried deep within
the logic fabric.
Moreover, your board and system
designs are also more complex and densely
packaged. Whether you’re troubleshooting
in the lab or in the field, your access to signals
in the FPGA, on the board, or in the
system is very restricted.
The Xilinx ChipScope™ Pro integrated
logic analyzer (ILA) has solved much of
the problem at the FPGA level. You can
embed its real-time data collection and
reporting cores in your FPGA to provide
visibility to internal FPGA signals and
events.
But if that’s all you’re using
ChipScope for, you’re not getting the
most out of this powerful tool. With a
little forethought during the design of
your board and system, you can extract
more value from the ChipScope Pro ILA
during the entire product life cycle –
from initial debug of board-level signals
in the lab through system diagnosis and
maintenance in the field.
ChipScope Pro – A Review
ChipScope Pro is a “logic analyzer in an
FPGA.” It provides real-time debug and verification
capabilities for your FPGA design.
You can find all the details about the
ChipScope Pro ILA at www.xilinx.com/ise/verification/chipscope_pro.htm.
You interact with ChipScope Pro using
a familiar logic analyzer interface running
on your PC, which is connected to your
hardware under test via a JTAG interface.
Figure 1 illustrates a simple ChipScope
Pro design example.
ChipScope Pro Basics
The ChipScope Pro program consists of
two main core types in the FPGA, plus
software running on your PC:
- ILA core – With the assistance of a
core inserter program, you embed the
ChipScope Pro ILA core in your
FPGA design to collect data when trigger
conditions are satisfied. You can
easily tailor the data size, target signals,
and basic trigger architecture during
the design phase. You can set flexible
trigger conditions at debug time.
(Target signals can be changed using
the Xilinx FPGA editor probe tool
without requiring re-synthesis, replace,
or re-route of your design.) As
many as 15 ILA cores can be embedded
into one FPGA.
- ICON core – You embed the integrated
controller (ICON) core in
your FPGA design to control as
many as 15 ILA cores. This ICON
core governs each ILA core and
communicates with the ChipScope
software running on your PC over
the JTAG interface and the Xilinx
Parallel IV or MultiLINX™ cable.
- ChipScope PC software – You interact
with the hardware under test
using ChipScope Pro software running
on your PC. You spend minimal
time learning to use this
software, because it is so similar to a
hardware logic analyzer. You can set
trigger conditions and examine collected
data using this software. You
can also export collected data in a
variety of file formats for analysis by
other tools, or for incorporation into
documentation.
ChipScope Pro at the Board Level
Consider this: As the lead engineer for a
new board design, your job is to compose
the block diagram. Your knowledge and
duties include:
- Partitioning a multitude of complex
functions into various circuits on the
board
- Allocating many of the circuits to
reside in one or more Xilinx FPGAs on
the board
- Recognizing the need to provide a
means of debugging the many internal
FPGA designs
- Realizing that the ChipScope Pro tool
can economically provide visibility to
all FPGA signals
- Knowing that the ChipScope Pro tool
requires no more design resources than
the JTAG interface already provided
for FPGA configuration
- Using some incremental FPGA
resources (mostly block RAM) for
ChipScope Pro data collection.
Think Outside the Chip
While considering FPGA debug options,
you realize that:
- Your board design is very complex and
spatially dense.
- The board circuits outside your FPGAs
are not going to be any easier to debug
than the internal FPGA designs.
- You do not have room to provide test
point headers or connectors for all the
board signals that will require further
examination.
Should you route these board-level signals
to spare pins on the FPGA?
Yes – then you can connect the signals
to the ChipScope Pro ILA core provisioned
for internal FPGA signal debugging. If you
anticipate that your primary FPGA functional
designs will consume all of the I/O
pins or internal logic resources, you must
consider upgrading to the next package size
or logic density. The following benefits will
outweigh the incremental cost:
- Decreased debug and development time
- Flexible, permanent debug signal routing
- Built-in board-level instrumentation,
which leads to
- Reduced demand for scarce lab instruments
during peak debug activity.
Figure 2 illustrates ChipScope Pro utilized
as a board-level test tool. Notice its
similarity to Figure 1, where ChipScope
Pro is used as an FPGA-only tool.
ChipScope Pro at the System Level
You, as the system engineer for your company’s
sophisticated new product, must
achieve multiple objectives, such as:
- Ensuring that system development and
integration flow as smoothly as possible,
thus minimizing your time to market
- Providing an easily maintainable product
to minimize service costs for the
product’s overall life cycle.
Incorporate Instrumentation
What if every system that you integrate
and ship could include the capability of
built-in instrumentation? By utilizing the
same Xilinx ChipScope Pro program that
your board-level engineers use to debug
FPGA designs, you can configure your
products for system integration and field
maintenance.
This will cost you nothing more than a
few judiciously chosen system-level signals
routed to a Xilinx FPGA; some incremental
FPGA resources (mostly block RAM);
an accessible JTAG connector; and some
up-front system design time and planning.
These costs will be overshadowed by the
following benefits:
- Decreased system integration time
- Built-in system-level instrumentation
- Reduced demand for scarce lab instruments
during peak integration activity
- Flexible, permanent maintenance and
diagnostic signal routing.
During system integration, engineers
can connect a PC running ChipScope Pro
software to the system JTAG port, and
monitor system-level signals.
You don’t have to use a dedicated hardware
logic analyzer. Production test engineers
can readily adopt this capability and
use system signals during acceptance testing.
System installers can utilize ChipScope
Pro’s capability at customer sites to debug
problems, or to ensure proper operation.
Going forward, maintenance personnel can
troubleshoot system problems using no
more than a laptop PC running ChipScope
Pro software.
Figure 3 illustrates ChipScope Pro used
as a system-level test tool, which builds on
the board-level test tool of Figure 2.
Design Example
I developed the concept of extending
ChipScope Pro’s utility when I undertook a
design in my poorly equipped basement lab
using a Xilinx CoolRunner-II CPLD evaluation
board from NuHorizons Electronics.
Although the design was simple, I needed to
examine four or five dynamic signals simultaneously
on the CPLD board, equipped
with only a digital volt-amp-ohmmeter, and
no oscilloscope or logic analyzer.
Necessity Is the Mother of Invention
Fortunately, I also had a Xilinx evaluation
board containing a Virtex XCV400 FPGA.
Although this was a relatively small FPGA,
it was more than sufficient to house the
ChipScope Pro ICON core and a simple
eight-channel ILA core.
In this particular case, my implementation
of ChipScope Pro was the ultimate in
simplicity: no internal FPGA signals were
connected to the ILA core. Rather, the
eight ILA core data/trigger signals were
routed directly to I/O pins, which terminated
at a header on the FPGA evaluation
board. I connected wires to those pins,
which I then used as probes on my CPLD
board.
I was able to debug my CPLD design
after just a few iterations of coding, downloading,
and collection of data via the
ChipScope Pro software.
For the modest cost of the ChipScope
Pro utility, plus a small FPGA board and
JTAG cable, I discovered that you can
replicate the functionality of a logic analyzer
that would otherwise cost thousands
of dollars.
Some Suggestions
To utilize the ChipScope Pro software as
a board-level tool, follow these suggestions:
- Provide access to the FPGA’s
JTAG port.
- Anticipate which board-level signals
you might want to examine during
debug.
- Route these signals to the FPGA so
you will have board-level access.
- Dedicate some extra I/O pins on your
FPGA to accommodate board-level
signals requiring examination.
- Anticipate some extra internal FPGA
resources (mostly block RAM) for
ChipScope Pro’s collection of boardlevel
signal samples.
- After analyzing the dynamic properties
of the signals of interest, make sure
you have an appropriate clock signal
so the ChipScope Pro tool can process
your board-level signals.
To utilize the ChipScope Pro program as
a system-level tool, follow these suggestions:
- Provide access to an appropriate system-level JTAG port.
- Anticipate which system-level signals
you will want to examine during system
integration and life cycle support.
- Route these signals on boards and
backplanes or cables to the FPGA
chosen to host the system-level JTAG
interface.
- Dedicate adequate FPGA resources
(I/O pins and logic) to accommodate
the system-level signals of interest.
- After analyzing the dynamic properties
of the signals of interest, make sure
you have an appropriate clock signal so
ChipScope Pro can process your system-level signals.
- In the unlikely case that your system
contains no other FPGAs, it would be
worth the cost of a small FPGA in
which to embed the ChipScope Pro
core as an economical integrated
system-level logic analyzer.
Conclusion
You can add value to your FPGA-based
product by expanding the use of the
Xilinx ChipScope Pro integrated logic
analyzer “outside the chip” of the
FPGA design.
You have already invested in
ChipScope Pro for debugging the internal
FPGA design. You can decrease
your board- and system-level debug
time for zero additional tool costs, and
minimal up-front design time and
resources. Additionally, you can
enhance your product with permanent
system diagnostic and maintenance
capabilities for its entire life cycle.
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