AN 597: Getting Started Flow for Board Designs

AN 597: Getting Started Flow for Board Designs
AN 597: Getting Started Flow for
Board Designs
AN-597-1.1
© March 2010
This application note provides an overview of the Altera® FPGA design flow.
Introduction
In many system designs, the typical design flow begins with a Marketing
Requirements Document (MRD) that specifies both the high-level business
justifications and the technical requirements of the product to be developed. After
the document is approved, the responsible engineering team uses it to produce a
more detailed technical Product Requirements Document (PRD). The PRD typically
specifies the architectural implementation of the product and may even specify
certain key components required in the design implementation. Detailed design
specifications are generated by the design engineers from this PRD.
An FPGA is a key component that is frequently used in complex system designs
because of its programmable nature and integrated high-speed transceivers. Because
of this flexibility, FPGAs have become central to the system, allowing designers to
easily bridge different technologies and drive high-speed backplanes. However,
because of its flexible nature, designing with FPGAs can also present a challenge if
the designer is not fully familiar with the FPGA design process. This document
presents a quick overview of the Altera FPGA board design flow and provides links
to relevant additional information to ensure a successful and robust FPGA
implementation.
FPGA Design Flow
Figure 1 shows the typical design flow using an Altera FPGA device. The following
sections describe each relevant step in the FPGA design process. Where applicable,
links to related information are provided for further guidance.
© March 2010 Altera Corporation
AN 597: Getting Started Flow for Board Designs
Page 2
Device Selection
Figure 1. FPGA System Design Flow
FPGA HDL Design, Timing Closure, Verification, Synthesis, and SOF Generation
I/O &
Resources
OK?
Device
Selection
Symbol
Creation &
Verification
Yes
Schematic
Design
Power
Estimation
PCB
Stackup
Design
PDN &
Decoupling
Design
Check
Device
Errata
No
Thermal
Analysis
Design
Pre-Layout
Modeling &
Simulation
Finalize
Schematic
& Netlist
Generation
PCB
Layout
Post
Layout
Simulation
OK?
Yes
Layout
DRC &
DFM
Layout
Guidelines
PCB
Gerber Out
PCB
Fabrication
System
Bring-up
& Test
No
Device Selection
The typical FPGA design process begins with selecting the Altera FPGA device that
best meets the system’s requirements, such as the number of I/O pins, LVDS
channels, clock and PLL resources, amount of integrated RAM, DSP blocks, number
of transceivers, and so forth. When a device is selected that delivers the resources and
performance required, schematic and FPGA HDL design can proceed.
f
For information about device features and resources to aid with device selection, refer
to the Altera Product Selector.
Schematic Symbol Creation
Schematic capture begins with the creation of the FPGA symbol. Due to the
programmable nature of most I/O pins in the FPGA, careful pin planning at this stage
helps lessen layout complexity and reduce layer count. Use the following conventions
and the checklist in “User I/Os” on page 4 to create the schematic symbol:
■
Consider the system level floorplanning of the interconnected devices on the
board and assign pins that minimize signal crossings in the layout stage
■
Give programmable I/O pins names that reflect their intended function for better
schematic readability
■
Name dedicated pins such as configuration and power pins according to their
dedicated function
AN 597: Getting Started Flow for Board Designs
© March 2010 Altera Corporation
Schematic Design
Page 3
■
Compile the final pin assignments in Altera’s Quartus® II design compiler
software to ensure the pin assignments meet the device requirements and I/O
placement rules
f
For the complete Altera FPGA device family pin-out files to help with the schematic
symbol creation, refer to the Pin-Out Files for Altera Devices web page.
f
Users of Cadence’s Capture schematic tool can download the premade Altera
schematic symbol libraries from the Cadence Capture CIS and Allegro PCB Symbols
and Footprints web page.
Schematic Design
When a verified symbol is complete, the schematic capture connects all FPGA pins to
their respective interfaces according to their usage requirements.
f
Refer to the Altera Pin Connection Guidelines for the device selected to ensure that
any specific Altera recommendations or requirements are met.
f
Use the appropriate Device Schematic Review Worksheet to verify your schematic
connections and ensure that all Altera guidelines are correctly followed.
Altera FPGA pins can be divided into the following categories.
Configuration and JTAG Pins
Because FPGAs are SRAM-based devices, they require configuration data to be
reloaded each time the device powers up. These pins are used to program the FPGA
with Quartus II-generated configuration data. Some configuration pins are dedicated
for this purpose, while others can also be used as user I/O pins after device
configuration is complete. For flexibility, Altera devices support a wide variety of
configuration modes to satisfy the application requirement. Select one or more
configuration modes based on the design requirements.
f
For information about configuring Altera FPGA devices, refer to the Configuration
Center web page.
f
For detailed information about each configuration mode, refer to the Configuration
Handbook.
f
For additional training on configuring Altera FPGA devices, refer to the Configuring
Altera FPGAs online training course.
In addition to the configuration pins, Altera devices provide dedicated JTAG pins that
are always available for device programming and debugging, regardless of the
configuration mode selected. Always connect the JTAG pins to a 10-pin JTAG header
so device programming and the SignalTap II Embedded Logic Analyzer debugging
tool can be used with any of the available Altera download cables.
© March 2010 Altera Corporation
AN 597: Getting Started Flow for Board Designs
Page 4
Schematic Design
f
For more information about the SignalTap II Embedded Logic Analyzer, refer to the
Design Debugging Using the SignalTap II Embedded Logic Analyzer chapter in volume 3 of
the Quartus II Handbook.
f
For more information about Altera’s download cables, refer to the following
documents:
■
ByteBlaster II Download Cable User Guide
■
USB-Blaster Download Cable User Guide
■
EthernetBlaster Communications Cable User Guide
Clock and PLL Inputs
Clocking within the FPGA is divided into regions. For example, in Stratix IV devices,
the clock regions are driven by Global Clock (GCLK) networks, Regional Clock
(RCLK) networks, and PLL outputs. The dedicated clock input pins provide the
external clock sources to these GCLK and RCLK networks and PLLs within the
device. Because of the fixed location of the dedicated clock input pins and PLLs, not
all clock pins can drive all regions of the device and PLL resources. As a result, clock
pin assignments must consider internal clocking and PLL resources that are available
to the pin.
f
For detailed information about Clocking and PLL resources, refer to the Clock
Networks and PLLs chapter of the respective device handbook on the Literature and
Technical Documentation web page.
User I/Os
I/O pins are designed to support a wide range of industry I/O standards, allowing
the flexibility to easily interface with different technologies. I/O pins are arranged in
groups around the device called I/O banks. Depending on the device, these I/O pins
may provide added features such as dynamic On-Chip Termination (OCT),
programmable current strength, programmable slew rate, and programmable delay
for easy interfacing flexibility, improved signal integrity, and timing controls without
external components. However, because an I/O bank is restricted to a single I/O
power (VCCIO) and reference voltage (VREF) within the bank, mixing I/O standards
with different VCCIO or VREF voltages in the same bank is not allowed. As a result,
careful pin planning must be done to optimize pin and bank usage.
Use the following checklist for making I/O pin assignments:








Select a suitable signaling type and I/O standard for each I/O pin
Ensure that the appropriate I/O standard is supported in the targeted I/O bank
Place I/O pins that share the same voltage level in the same I/O bank
Verify that all output signals in each I/O bank drive out at the I/O bank’s VCCIO voltage level
Verify that all voltage-referenced signals in each I/O bank use the I/O bank’s VREF voltage level
Check I/O bank support for LVDS features
Use the dedicated DQ/DQS pins and DQ groups for memory interfaces
Validate the pin assignments in the Quartus II software
AN 597: Getting Started Flow for Board Designs
© March 2010 Altera Corporation
PCB Stackup Design
Page 5
f
For more information about user I/O pins, supported I/O standards, OCT, and other
I/O features, refer to the I/O Interface chapter of the appropriate device handbook on
the Literature and Technical Documentation web page.
f
For more information about using I/O pins for memory interfacing, refer to the
following links:
■
External Memory Solutions Center web page
■
External Memory Interfaces Handbook
■
External Memory Interfaces Design Examples web page
High-Speed Transceivers
High-speed transceiver pins are the multi-gigabit serial links used for implementing
high-speed interfaces such as PCI Express, SATA, 10G Ethernet, XAUI, Serial
RapidIO, and many others. Successful serial interface designs that use these pins
require a good understanding of high-speed design techniques to minimize I/O jitter
and maximize transceiver eye openings. For guidelines specific to transceiver design,
refer to the transceiver section of the device handbook for your selected device.
f
For general board design guidelines related to high-speed transceivers, refer to the
“Gigahertz Channel Design Considerations” section of the Board Design Resource
Center web page.
f
For additional gigabit channel design guidelines, refer to the Gigabit Channel Design
Guidelines web cast.
f
For a list of supported transceiver protocols by device family, refer to the Transceiver
Protocols web page.
Power Supplies
Power supply pins provide power to the digital and analog blocks that comprise the
core, I/O, PLLs, and transceivers. The analog PLL and transceiver’s power rails are
sensitive to noise and must be carefully isolated and decoupled to minimize noise
impact on performance. Power rail isolation can be defined in both the PCB stackup
design and the layout of the board. For more information about decoupling, refer to
“Power Design and Decoupling”.
PCB Stackup Design
In parallel with the schematic capture process, the PCB stackup design is usually
specified by working closely with the PCB fabrication vendor. Most PCB vendors
freely provide the detailed stackup design to fit the engineering requirements. A
typical stackup usually specifies the PCB and dielectric material, the number of layers
(signal, power, and ground), the ordering of the layers within the stackup, the trace
geometry and impedance control requirements, the PCB board paneling to maximize
boards per panel, and the finished board thickness. Having a final PCB stackup
design early is useful for performing pre-layout signal integrity simulations that can
be used to derive the layout design rules required for the PCB layout designers.
© March 2010 Altera Corporation
AN 597: Getting Started Flow for Board Designs
Page 6
Power Design and Decoupling
f
For more information about PCB stackup considerations, refer to the “PCB and
Stackup Design Considerations” section on Altera’s Board Design Resource Center
web page.
Power Design and Decoupling
A challenging part of designing with FPGAs is the implementation of the power
distribution and decoupling network. Because the power requirements of an FPGA
can vary significantly depending on the FPGA design, the optimum decoupling
depends on the actual current draw of each rail of the FPGA. The strategy for
determining the optimum FPGA decoupling starts with an estimation of the device’s
power requirements and using the Frequency Domain Target Impedance Method
(FDTIM) to realize the decoupling network for the device.
f
Use the Altera PowerPlay Early Power Estimator (EPE) tool and the PowerPlay Power
Analyzer tool in the Quartus II software to obtain an accurate estimate of power
throughout the FPGA design process.
f
Use the Altera Power Distribution Network (PDN) Design Tool to determine the
decoupling requirements.
f
For more information about using the PDN tool and FDTIM methodology, refer to the
following links:
■
Power Distribution Network Design for Stratix III and Stratix IV FPGAs (OPDN1100)
online training course
■
“Power Distribution Network (PDN) Design” section on the Board Design
Resource Center web page
■
AN 574: Printed Circuit Board (PCB) Power Delivery Network (PDN) Design
Methodology
Thermal Management
In addition to power estimation, the EPE tool also estimates die junction temperature
(Tj) based on the expected system ambient temperature (Ta) and junction-to-ambient
thermal resistance (θja). Using the EPE tool, you can determine the heat sink or
airflow required to maintain the FPGA’s junction temperature at safe operating
conditions.
f
For more information about thermal management, refer to the “Power Dissipation
and Thermal Management” section on the Board Design Resource Center web page.
f
Users of the Mentor Graphics® FloTHERM thermal modeling software tool can
download FloTHERM device thermal models from the “Thermal Models” section
on the Board Design Resource Center web page.
AN 597: Getting Started Flow for Board Designs
© March 2010 Altera Corporation
Pre-Layout Simulation
Page 7
Pre-Layout Simulation
To verify the signal integrity of critical routes in the system, Altera provides complete
IBIS and HSPICE I/O buffer models to allow system designers to perform
hypothetical scenarios for the signal integrity simulations. This can be useful for
determining termination requirements, crosstalk effects, length constraints, and
other layout design rules for critical nets.
f
For a list of available IBIS and HSPICE I/O buffer models, refer to the following web
pages:
■
Altera IBIS Models
■
SPICE Models for Altera Devices
Layout Design
The layout design is the process of translating the schematic design into the physical
representation of the board. A common practice is to provide the layout designer with
a detailed document that specifies all the physical requirements required for the
board’s layout. This document usually contains the detailed board dimensions, the
stackup information with layer construction (which was done previously in
collaboration with the PCB vendor), all necessary design rules derived from the
pre-layout simulations to meet signal integrity, and any design rules that are
necessary to meet board manufacturing requirements. When the layout designer has
reviewed and understood these requirements, layout begins with the component
symbol (or footprint) creation, detailed component placement, and design rule entry
into the layout design tool.
f
To aid in the rules creation for the sensitive gigabit transceiver channel routing, Altera
provides the following application notes:
■
AN 529: Via Optimization Techniques for High-Speed Channel Designs
■
AN 530: Optimizing Impedance Discontinuity Caused by Surface Mount Pads for
High-Speed Channel Designs
f
For information about Altera’s packaging information for device footprint creation,
refer to the Altera Device Package Information Data Sheet.
f
Users of Cadence’s Allegro PCB layout tool can download the premade Altera
Allegro symbol libraries from the Cadence Capture CIS and Allegro PCB Symbols
and Footprints web page.
© March 2010 Altera Corporation
AN 597: Getting Started Flow for Board Designs
Page 8
Post-Layout Simulation
Post-Layout Simulation
When the critical routes of the layout design have been completed, Altera
recommends you perform a post-layout extraction and simulation on those critical
nets to validate their expected signal integrity behavior. Similar to the pre-layout
simulation already discussed, the post-layout simulation can use the device IBIS and
HSPICE I/O buffer models along with the extracted layout S-parameter data to
generate a simulation deck. When the post-layout simulation confirms proper signal
integrity behavior, the layout can be finalized and released for final checking and
generation of Gerber files for the PCB.
Conclusion
FPGAs are commonly used in complex system designs due to their high integration
and flexibility. However, this flexibility can present unique challenges in the system
design process. This application note provides an overview of the Altera FPGA design
flow to help familiarize you with the Altera FPGA design process. Links to additional
information are provided throughout the document to help you successfully design
with Altera FPGA devices.
Document Revision History
Table 1 shows the revision history for this application note.
Table 1. Document Revision History
Date
Version
Changes Made
March 2010
1.1
Added link to Device Schematic Review Worksheets in “Schematic Design”.
March 2010
1.0
Initial release.
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information and before placing orders for products or services.
AN 597: Getting Started Flow for Board Designs
© March 2010 Altera Corporation
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