Over the past ten years the aerospace industry has adopted the use of commercial off-the-shelf (COTS) electronics as a means to rapidly design and deploy embedded processing systems. However, the integration of dozens of general-purpose processors in a real-time architecture is not an easy task. The advent of platform field-programmable gate arrays (FPGAs) with advanced system design features such as embedded PowerPC and multi-gigabit transceivers is changing the game of aerospace system design. The convergence of hardware, software, memory and multi-gigabit signaling offers the opportunity to engage in system-level design at the chip level.
As an example, The Boeing Co.'s state-of-the-art airborne, electro-optical imaging system, currently in the design stage, will provide exceptional surveillance and engagement capability for aircraft in the 21st century. To achieve the design objectives, Boeing designers are integrating a broad array of technolo gies into a complete programmable system.
Key design elements include:
- A high-resolution gimbaled telescope driven by line-of-sight control electronics. This system implements control algorithms that accept operator inputs to point the telescope to ground-based objects of interest.
- Precision optics direct the light collected by the telescope into a series of imaging cameras. Aircraft engine vibration, structural resonance and other disturbances can wreak havoc on the alignment of these devices. To compensate for these effects, an automatic alignment system is incorporated.
- Sensitive imaging cameras act as the eyes of the electro-optical payload. These devices provide high-resolution daytime and nighttime video to real-time image-processing hardware.
- Sophisticated image-processing algorithms perform video enhancement, segmentation and feature extraction.
The platform FPGA played a critical role in the design of the embedded-processor architecture for this application, formin g the centerpiece of the processor architecture. Numerous system functions are supported, including high-speed image processing, digital-video scene generation and storage, fiber-optic media conversion of video data, Digital Video Interactive display generation, NTSC video generation, servo-control functions, and automatic alignment of precision optics.
Boeing's design team incorporated many signal-processing functions into the platform FPGA. Among these were the following:
- The high-performance logic fabric and embedded multipliers offer the parallel processing needed for the repetitive, systolic nature of our algorithms. Single FPGA devices replaced and outperform what once would have been multiple digital signal processors (DSP) or PowerPC processors.
- The wealth of interface pins can easily be configured for different signaling standards and devices. Boeing's designers can implement a PCI bus interface, video encoder/decoder connections, digital-video display out puts, multiple SRAM interfaces, and a high-speed digital-video input port using a single programmable device. These functions run in parallel, concurrently, without the hassles of bus contention and multiprocessor scatter/gather issues.
- The embedded IBM PowerPC 405 CPU can be employed to perform back-end software-based computations. Representative applications include mode logic, control-loop management and configuration of hardware-based pre-processing.
The embedded CPU offers highly useful capabilities when considered in a system design context. Using the programmable logic to accelerate the embedded CPU, the residual back-end processing for Boeing's application required only a modest amount of compute power. The embedded processor consumes a fraction of the power of a high-end CPU, while remaining directly coupled to the logic fabric. Data transfer between the buried processor and FPGA application can be accomplished in a far more creative and efficient manner than by using an external digital signal processor or microprocessor. For many applications, the embedded PowerPC provides the right balance of performance, power, interface and general-purpose computing capability.
Boeing's design team used the embedded CPU as a microcontroller. Without the real-time operating system, cycle efficiency and determinism became more predictable. This enables real-time hardware and software reconfigurability--in real-time. A single unified bitstream defines the operating characteristics for both the CPU and logic.
In addition to the embedded CPU, Boeing's design team makes use of almost every major feature of the platform FPGA logic fabric. The dual-port block RAM is a veritable Swiss Army knife in terms of functionality. It can be used for tapped delay lines, command and status data buffers, lookup tables, bus-width conversion, FIFOs, etc. The SRL16 capability, distributed RAM and dedicated fast-carry logic offer a key advantage in DSP applications. These features are critical to the design of high-perf ormance digital filters and also help to significantly reduce the associated logic footprint. Digitally controlled impedance technology is a useful aid when implementing functions such as double-data rate (DDR) RAM interfaces. Boeing's printed-circuit board designer no longer struggles with finding a way to place hundreds of termination resistors.
The digital clock managers (DCMs) enable Boeing to leverage both the frequency synthesis and precision phase-shifting capabilities to ensure reliable and predictable timing behavior. The multi-gigabit transceivers are one of the most important additions to the FPGA logic fabric. High-speed fiber-optic data transfers can be directly coupled to algorithms running inside the hardware. This provided Boeing designers with the freedom to employ their own simplified protocols where switched-fabric interconnects would be overkill.
Christopher Musial is real-time systems engineer at The Boeing Co. (Seattle, Wash.) and Katie DaCosta is solutions marketing manager , DSP solutions, at Xilinx Inc. (San Jose, Calif.).
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