Altera has beefed up its Nios soft-core embedded processor, adding user-configurable L1 instruction and data caches, enhanced SDRAM controller, enhanced Avalon Switch Fabric, and a JTAG-based real-time debugger to version 3.0. A network protocol library that Altera previously sold separately for $450 is now also included with Nios.
Nios is a general-use RISC processor that can be combined with user logic and programmed into an Altera field-programmable gate array (FPGA).
According to Altera, the L1 instruction and data caches are better able under version 3.0 to use the dual-port memories on Altera's Cyclone and Stratix FPGAs. The enhanced SDRAM controller now enables single-cycle access to low-cost SDRAM devices at speeds above 100MHz. The Avalon switch fabric (Altera's parameterized interface bus used by the Nios processor) now supports pipelined data transactions to eliminate data bottlenecks. The JTAG-based debugger, the OCI (On-Chip Instrumentation) core from First Silicon Solutions, is accessed through a JTAG target connection and supports complex hardware triggers and real-time trace.
More development help is now available. Altera has released a Nios/Stratix development kit with a Stratix development board and plans to release kits for their Cyclone FPGAs in the coming months. Nios is compatible with the code|lab Developer Suite and Nucleus real-time operating system. Altera provides a way for developers to convert an FPGA-targeted design icorporating the Nios processor into an ASIC.
Different from your average core
As a soft-core processor for FPGAs, Nios is almost in a class by itself. Xilinx also makes a processor, MicroBlaze, for their FPGAs Spartan and Virtex. These two soft-core processors are the only ones specifically designed to work where most processors flounder-in an FPGA.
"Most microprocessors (ARM, ARC, MIPS, Tensilica, PowerPC, etc.) don't work very well in FPGA chips. There are a lot of technical reasons for this," explains Jim Turley, semiconductor analyst and contributing editor for Embedded Systems Programming magazine. "Nios and MicroBlaze are both reasonable processors, but they have limitations imposed by their FPGA underpinnings. The internal silicon structure of an FPGA doesn't lend itself well to microprocessors. That's why we don't see Pentium, MIPS, PowerPC, ARM, and other mainstream processors implemented in programmable FPGA logic."
It is because of these limitations that Altera and Xilinx developed their own CPU cores to work in their FPGAs. These processors are not meant to compete with mainstream processors because they're working in an FPGA. The tradeoffs are moderate performance and clock speeds, which are 100MHz or less in most cases. They also consume a lot of power for their size and performance, says Turley.
Interest rises
Despite the high costs of FPGAs (Altera's Stratix costs $250 to $800 each, while the much smaller Cyclone runs $4 to $20 each), engineers have begun to show interest in Nios since its introduction in the fall of 2000. The tally of engineer responses in the Embedded Systems Programming 2002 Subscriber Study, not yet publicly released, shows that Nios is on their radar, whether engineers are using it or just curious about it. Altera claims more than 10,000 hardware development kits have shipped in over two years and that Nios is appealing to the engineers who want to switch to ASICs on the cheap, not just the FPGA folks. It's also appealing to software engineers in addition to hardware engineers, which is affecting how Altera markets the product.
Turley says, however, that the FPGA is the key. "Customers using Nios or MicroBlaze choose their FPGA first and their CPU second. In other words, they select Altera (or Xilinx) FPGA chips, then they accept whatever processor the FPGA company promotes. I don't think anyone chooses Altera because of Nios, or Xilinx because of MicroBlaze. It's the other way around."
At this time "Nios doesn't have much software support," adds Turley. "There are virtually no experienced Nios programmers, and a very limited selection of Nios software. Operating systems, debuggers, emulators, and so on are in short supply. Again, this may not matter to everyone. The tools Altera supplies might be good enough. But Nios will never rival PowerPC (or ARM, or MIPS, or SPARC, etc.) for developer support."
Developer support is subject to change as more companies use the Nios core. Some companies currently using Nios include Philips Business Communications for its reconfigurable protocol handler for its SOPHO iS3000 series of iSPBXs; Alcatel for SDH/SONET Transmission in its Optical Multi-Service Node; and Kodak in its general control processor for its Digital Cinema System.
The Nios embedded processor is royalty free when used in Altera FPGAs and HardCopy ASICs. Nios is now shipping with the Stratix edition developer kit for $995; renewals of expired Nios subscriptions are $495 for one year of updates, while active Nios subscribers get the 3.0 version immediately for free. ASIC licensing is available.
