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DSP Boards: A Buyer's Guide
By Henry Davis
Fortunately, it's not necessary for a designer to start from scratch when dealing with complex DSP chips, an essential component for many communication systems- thanks to an array of preconfigured and customizable DSP boards and related software.
As the digital signal processor (DSP) business has matured, the closely allied technology of DSP boards has grown by leaps and bounds. Nearly any product need can be met by standard off-the-shelf DSP-based boards and related board products. Specialized DSP board offerings intended for application-specific usage provide a wide range of performance, capability, and price.
The development of DSP boards, like many other board-level technologies, grew out of the DSP manufacturer's evaluation-board offerings. These evaluation boards were often low-cost, simple, stand-alone products that offered enough hardware capabilities for engineers to gain familiarity with the underlying DSP processors. Central to the board designs was a wire-wrap breadboarding area intended for engineers to prototype special circuitry during the product-evaluation phase of DSP selection.
The capabilities of DSP boards have diverged from evaluation boards in several important ways -- most notably in form, function, and capacity.
Determining form factors
Form is largely determined by the bus supported by the DSP board. In many cases, the existing installed base of systems based on a specific bus determines which bus must be used for DSP boards. For these situations, the bus form dictates the selection of DSP boards. Where DSP vendors' evaluation boards were typically stand-alone with no complete standard bus, the form of commercially available DSP boards has em-braced a variety of bus standards. Commonly supported buses include CompactPCI (CPCI), PCI, the PC ISA bus, and VME. There are DSP boards available for nearly every bus in common usage in the US, Europe, and Japan. From the bus standards standpoint, the only real issue, apart from technical issues of performance, is the variety of boards available for a specific bus standard.
Function, apart from the bus standard, is one of the top priorities for producers of DSP boards of all types. There is a bewildering array of DSP and peripheral boards available for almost any application. From digital radios to low-power industrial-control A/D converters, DSP board vendors can satisfy all but the most esoteric or specialized needs. The trick is choosing the right bus, DSP processor, and selection of board vendors to build a specific system.
Regarding capacity, in the last few years DSP board vendors have made unprecedented amounts of processing power available. The initial impetus for DSP boards was to provide the raw processing capacity of DSP processors in a standardized package available to engineers creating systems that were produced in quantities too small to be cost-effectively manufactured as specific-produced boards. This focus led to a fairly predictable progression of DSP-based boards. Vendors started by featuring a board that included a single DSP. Decisions about which board to use largely centered on the choice of processor. Choose an Analog Devices ADSP2100 processor and you had a specific set of options. If your choice was a TI TMS320C50, you had a different set of options.
Rather than simply providing a DSP board with a single DSP processor and minimal support circuitry, vendors now can offer processor boards with incredible power and capability. Where DSP boards once held a single processor, some vendors now offer up to eight of the most powerful DSPs on a single card, and it is possible to operate multiple cards in a single system for even more power.
A non-traditional approach
Not all DSP boards implement a specific bus standard in the traditional meaning of bus. One of these boards is the TIM-40. Short for Texas Instruments Module, a form-factor devised by Texas Instruments (TI) (www.ti.com), the standard defines a common module format specific to the TMS320C4x. In a twist of standards setting, a consortium was formed to write the "TIM-40 TMS320C4x Module Specification," which is edited and published by TI, but is controlled by the consortium (which has voting rights on any proposed changes).
TIM-40 is an open standard designed to simplify the integration of multiple TMS320C4xs with communication ports into a system. Each TIM-40 module is a daughter board that may contain one or more TMS320C4x parallel DSP processors, with any type of memory, I/O interfaces, and other functions. Although the standard is processor-centric, it is also possible to implement communication port-based I/O functions that do not require a processor.
TIM-40 modules may be mounted on a range of host carriers such as PC/AT add-in boards, expansion boards for VME, or Sbus-based systems. The carriers may conform to any standard as long as the module slots conform to the TIM-40 standard. Modules may be double width, triple width, or larger, thereby occupying more carrier area. These modules may be used to support other modules consisting of more than one DSP or a large amount of peripheral circuitry. Modules are connected to the carrier by two connectors. Each connector carries control signals, power, ground, and a number of communication ports intended to support distributed systems.
An optional global expansion connector provides access to the 'C4x global bus in shared-memory systems. The 'C4x JTAG interface is available on the TIM-40 connectors, allowing parallel-processing emulation with TIM-40s. By using JTAG and the capabilities of the TI JTAG emulation system, a single emulation connection allows the debugging of any number of TIMs in the system. The number of modules in a system is limited only by the available space, power, and cooling facilities.
Traquair (www.traquair.com) was the first American company to ship TIM-40 hardware, and they have extended that technology tradition by offering an enhanced version of the module standard. Based on Hunt Engineering's (www.hunteng.co.uk) Hunt Engineering ResOurce Node (HERON), the new products are based on the new standard for modular real-time systems. HERON is not a processing standard, as the TIM-40 was, nor is it processor dependent. Instead, the open standard provides the capability to build resource nodes, which can be processors, I/O, or communications.
HERON takes flight
Where TIM-40 was an industry standard created by a consortium, HERON relies on Hunt Engineering's experience with TIM-40. Like TIM-40, HERON is an open standard -- the "HERON Specification" is published on Hunt Engineering's Web site along with all the necessary information. This simplifies designing custom HERON resource nodes while permitting the reuse of standard processors, module-carrier boards, or I/O.
The HERON DSP system family of products includes HERON processor modules and HERON data acquisition and I/O modules. These modules can be installed in HERON carrier boards. HERON DSP carrier boards combine and utilize multiple processors, data acquisition, and I/O interface modules, including PCI, VME, and CPCI configurations. Processor modules include high-performance TMS320C6000 DSPs or Virtex FPGA processors fitted with an amount and type of memory appropriate for the type of processor being used, an internal clock, and a FIFO interface.
One HERON module carrier board, the HEPC9, provides modular support for multiple processors and I/O interfaces. Each board supports four HERON modules. Each HERON module includes a TMS320C6000-based DSP processor with memory, such as the HERON1-C6201 and HERON1-C6701, or an I/O interface. As a result, each HEPC9 can be configured with an arbitrary combination of TMS320C62x (1,600 MIPS and up) fixed-point DSPs, TMS320C67x (1 GFLOP and up) floating-point DSPs, and I/O interfaces.
Existing peripheral GDIO I/O modules plug directly into the module slots of HERON DSP systems and are fully integrated within the HERON DSP system software framework. Engineers can combine the wide variety of processing capabilities offered by HERON DSP systems with analog, digital, communication, and video I/O capabilities.
Using the HERON system, the selection of modular resources is based only on application needs. Therefore developers are able to establish system configurations that are tailored to the application. Being able to fine-tune a hardware system to an application's needs in this manner leads to a shorter development cycle. While the general design methodology has been described in the HERON context, many of the benefits are available with most board-level products. Each system has a different set of strengths and weaknesses.
A Whole new spectrum
Where the HERON system is intended to address the physical aspects of DSP boards, Spectrum Signal Processing offers both bare DSP boards and application-specific systems that include DSP processing capability, specialty circuitry, and software to get engineers started quickly in complex system design.
One of these products is Spectrum's flexComm product line for wireless communications. It consists of baseband-processing engines, narrowband and wideband transceivers, and a digital radio software suite. Spectrum offers a wide range of PCI, CPCI, VME, and VXI baseband-processing DSP boards for applications that require system reconfiguration. Their narrowband and wideband subsystems have the highest channel density available with their unique "one-tuner, many signals" design. This flexibility enables a truly flexible software radio architecture. Coupled with Spectrum's digital radio system-level software suite for rapid prototyping is a range of professional services that are geared to supplement customers' engineering departments.
The Spectrum solution is well suited for development and deployment of 3G cellular base stations, but the individual boards are useful in a wide variety of applications. The application-specific products that make up flexComm are specifically aimed at systems employing any or all of the 3G air-interface standards, such as wideband-CDMA (W-CDMA), cdma2000, UMTS, and UTRA (ETSI W-CDMA). The flexComm wideband solution offers the capability to process four 30-MHz wideband channels in a single slot, or up to 24 channels in a CPCI chassis. By incorporating programmable FPGA preprocessing, it has the ability to partition 3G algorithms so that the extreme processing demands of W-CDMA do not overwhelm the baseband-processing engines. It also takes advantage of Spectrum's digital radio architecture, which allows one tuner to feed many signals to the digital down-converters and baseband-processing engines. The result is greater algorithmic flexibility.
Digital radio wizardry
In an approach that is gaining favor among DSP board vendors, Spectrum offers software called Digital Radio Wizard for easy hardware configuration, allowing software developers to focus on rapid development and deployment of their 3G algorithms.
Spectrum's single-slot Digital Radio QuickStart kits are designed to reduce the development cycle. These kits augment a basic DSP QuickStart kit by providing an A/D module, a digital receiver module, digital radio software tools, code-generation tools, a debugging solution, and all the necessary cables and documentation for platforms including: PCI (Daytona and Ingliston), VME (Monaco), and CPCI (Barcelona). The technical details for each DSP board varies according to the bus that it uses. The Monaco VME DSP board includes:
A 6U VME board with a VME64 master/slave interface. Each 'C6000 DSP on the Monaco can directly master the VMEbus
Processor choice
Dual or quad 1,600-MIPS, 200-MHz TMS320C6201B DSPs
Dual or quad 1-GFLOPS, 167-MHz TMS320C6701 DSPs
2 Mbytes of SBSRAM (max) and 64 Mbytes of SDRAM (max)
Hurricane, a single-chip PCI bridge ASIC optimized for DSP systems
Flexible I/O interfaces:
Two PEM sites that provide 400 Mbytes/s per DSP
One PMC provides 132 Mbytes/s throughput
DSP~LINK3 up to 30 Mbytes/s of I/O bandwidth.
Enter Voice-over-packet
In another application-specific product offering, DSP Research provides voice-over-IP (VoIP) solutions. VIPER boards are high-density DSP resource boards for computer telephony and telecom infrastructure applications such as voice-over-packet (VoP) gateways, remote access servers (RAS), and cellular base stations. Based on the powerful 'C54x and 'C6x DSPs from Texas Instruments, the VIPER boards increase channel density and reduce costs of these applications. VIPER boards are available for the CPCI, PCI, and ISA buses.
Typical of the DSP board approach to VoIP, the VIPER NGEN combines the power of 32 TI's 'C5420 DSPs with eight telephony I/O ports, an Ethernet interface, and a CPU to provide telecom systems integrators and OEMs with a fully integrated, VoP application board. This VoP board provides up to 320 simultaneous channels of H.323 (G.723 and G.729A). Other DSPs and system buses are supported by other boards:
VIPER-48 5420/CPCI. The VIPER-48 5420/cPCI board combines the speed and integrity of the CPCI bus and the density of the H.110 telephony bus with the power of 24 TI's 'C5420 DSPs to provide up to 240 channels of H.323 (G.723 and G.729A) per board.
VIPER 54x/PCI. VIPER 54x/PCI boards are high-density DSP resource boards that offer up to 12 'C54x DSPs and an multivendor integration protocol (MVIP) telephony bus. The board can support up to 60 channels of VoP (G.723 and G.729A).
VIPER 6x/PCI. The VIPER 6201/PCI board is the newest addition to the VIPER family of high-density MVIP DSP resource boards. With a single, the VIPER increases channel density and reduces costs of these applications. The VIPER features a 1,600-MIPS TMS320C6201 DSP on-board, MVIP, and/or T1/E1 interfaces for access to multiple 64-kbps data streams. For communications with the host PC, the board supports the C6201 host port interface (HPI), which offers shared access to the entire memory space of the 'C6201. Key features of the VIPER 6x/PCI include a TMS320C6201 running at 1600 MIPS; up to 1 Mbyte SBSRAM, 128 kbytes of SRAM, 512 kbytes optional Flash, and up to 16 Mbytes SDRAM. The board supports 'C6201 16-bit parallel HPI and features a 32-bit, 33 MHz master/slave PCI bus interface, an MVIP bus interface (Mitel flexible MVIP IC, MT90810), and a T1 or E1 interface. Additionally, the board sports an on-board JTAG emulator hardware and complete solution software/hardware bundles.
Atlas shrugs
Eonic (www.eonic.com) is taking another view on the subject of configurability and application-specific support. The company offers two entry-level products, the QuickStart Atlas I and the QuickStart Atlas II. Both Atlas systems come in a 19-inch, 3U ruggedized enclosure with a single Atlas board. The Atlas I board has two 120-MFLOPS floating-point ADSP-21060 processors, and the Atlas II board has two 480-MFLOPS ADSP-21160 processors. Each Atlas board also has 2 Mbytes of SBSRAM, boot Flash memory, a 30,000-gate Altera FLEX 10K30 FPGAs for building custom I/O interfaces, a PCI controller, two 16-bit industry pack (IP) slots, and a communication slot that can be tailored to accept CAN, USB, RS232, SPI, IRDA, and I2C communication modules. The Atlas system is preloaded with Eonic's Virtuoso suite of DSP development tools, which includes a preemptive, multitasking real-time operating system (RTOS). The host system is based on a 3U CPCI Pentium board from Innova Computers running Windows NT.
Additional members of the Atlas family will offer Tiger- SHARC, Power- PC G4, and TI's TMS320C6202 processors, as well as higher-density FLEX-10K50 and 20K400E FPGAs. Each board in the initial Atlas I Universal Digital Computer has a 30,000-gate Altera FLEX-10K30 FPGA for the implementation of custom interface logic and I/O decoupling -- getting data from the IP module and pumping it directly to the SHARC links without going through the CPCI bus. The FPGA logic can also be used to implement finer-grained datastream-driven algorithms, such as filtering for signals and pixel-level operations for high-speed image processing. Since the FPGA is reprogrammable, design changes can be made to the logic without redesigning the board. Higher-density FLEX-10K50 and 20K400E FPGAs will be offered with future Atlas versions.
Choices abound
Where engineers were once limited to DSP board choices based on processor type and the bus employed on the board, today's engineers have a wide variety of options that address many different needs. If the processor type is the critical parameter, there are a large number of suppliers -- choosing one is a straightforward task. If the bus is the critical issue, there are more choices today than just a few years ago. By employing mezzanine boards, it is possible to mix and match processor type, speed, and system bus.
The most exciting development in DSP boards is not the boards themselves. Rather, it is in the support that companies offer surrounding their products. Matching applications, software, and hardware is easier than ever before -- but there's also a lot more work due to the wide variety of alternatives. For nearly any application that uses DSP boards, there is an ideal solution available off-the-shelf -- finding it can be hard work.
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