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programmablelogicZONE Products for the week of July 14, 2008
Atmel Says…
ARM7-based MCU with FPGA Interface Offers Seamless Migration to Lower-Cost, Lower-Power CAP7 customizable MCUs
CAP7E multi-layer AHB interface and efficient DMA channels help accelerate ARM7-plus-FPGA designs
Atmel Corporation has announced the AT91CAP7E, the industry's first ARM7-based MCU with a direct FPGA interface. The AT91CAP7E is a standard microcontroller with an FPGA interface that makes the FPGA look and work like it is on the internal bus of the MCU. It provides customers with a two-chip, no-NRE, FPGA-plus ARM7 solution and offers an engineering-free migration path to a lower cost, and a lower power customizable MCU.
The CAP7E includes a six-layer advanced high-speed bus (AHB), peripheral DMA controller and 160 Kbytes of on-chip SRAM. On chip peripherals include USB 2.0 full speed device, SPI master and slave, two USARTs, three 16-bit timer counters, an 8-channel/ 10-bit analog to digital converter, plus a full-functioned system controller including interrupt and power control and supervisory functions. The FPGA interface on the CAP7E provides the FPGA with direct access to the CAP7E's on-chip AHB and peripheral DMA controller. This architecture eliminates FPGA-induced bus contention, off-loads MCU-to-FPGA communications from the CPU, and frees up the external bus interface for external memory access.
Interfacing an ARM7-based MCU to an FPGA has traditionally been done through the external bus interface (EBI) or programmable I/O. Either arrangement requires that the CPU transfer data to and from the FPGA one word-at-a-time, basically stealing CPU cycles that should be conserved for processing and limiting access to external memory during FPGA operations.
The FPGA interface on Atmel's CAP7E provides the FPGA with two AHB masters, four AHB slaves, a special direct AHB slave interface to an external RAM through the FPGA, and a programmable ROM that remaps the external RAM to emulate and debug the ROM code. Fourteen advanced peripheral bus (APB) slaves, two full-duplex DMA channels and 32-bit programmable I/O may be hardware selected to share I/O. An on-chip priority interrupt controller provides up to 13 encoded interrupts and two additional un-encoded interrupts for DMA transfers.
Third-party Tools and IP
The same C-compilers, RTOS, ICEs and IDEs used with Atmel's AT91SAM ARM-based MCUs can be used with CAP. Atmel has an extensive portfolio of silicon-proven peripherals that are available free of charge to customers migrating to a customizable MCU.
About CAP7 Customizable MCUs
Atmel's CAP7 customizable MCU is an ARM7-based microcontroller with a metal-programmable (MP) block with 450K gates or the equivalent of 56K FPGA logic cells (LC). Any functionality that has been implemented in an FPGA may be migrated directly to a CAP7 device with no special EDA tools or customer-side engineering. Standard FPGA software tools are all that is necessary to implement functions such as LCD controllers, DSP algorithms (e.g. GPS correlators, FFTs, FIR filters), and proprietary customer IP. A CAP7 implementation delivers as much as 8X better performance, consumes 98% less static power, and costs about 30% less than the FPGA-plus-MCU implementation.
EN-Genius Says…
An unnamed source at Atmel says that FPGAs are the heroin of the electronics industry and that their ARM7 processors which feature a large array of metal-programmable logic are part of the cure. If that’s true, one could look at the new FPGA-friendly variant of their I/O-encrusted customizable controllers as a sort of digital methadone that engineers can use to quickly prototype their designs and get them into alpha production as they tool up the masks for an FPGA-free hardcopy. Nevertheless, I suspect that many designers will find them handy in medium-volume applications which wouldn’t justify the $150 k tooling charge required to configure their metal-programmable logic array. However they are used, Atmel’s inclusion of a two AHB masters, four AHB slaves and a very efficient DMA interface on their CAP7E device makes it easy to take advantage of the new generation of lower-power, lower-cost FPGAs to add your own hardware accelerators or other proprietary IP to your next embedded design.
Given Atmel's philosophy, it’s no wonder then they’ve deliberately structured the price of the CAP7E to strongly encourage you to cough up the $150 k tooling charge it takes to go to a hard copy version as soon as your production hits any appreciable volume (probably around 20 – 50 k units). If you can fit your design into 250 k ASIC gates (approximately 25 – 30 k LEs) a CAP7 in a 144-pin BGA can cost as little as $5.50 in 10-k unit volumes. If you need something larger, there is a 450 k-Gate (around 56 k LE) version available for around a dollar more which is still a big savings over the $9.50 you’d pay for the HBA-equipped CAP7E plus the $5 - $10 you’d pay for a small FPGA. Atmel says that it is working on other variants of the CAP7 with up to 1 M gates that will accommodate complex signal processing applications like H.264 video compression.
While Atmel’s CAP7 developer board uses Xilinx low-cost Spartan 3 series (variants of which were reviewed here in March 2008 and April 2007), the processor interface works equally well with Altera’s competing Cyclone III series ( reviewed in March 2007). If your application requires higher density or speed, you can also use the processor’s AHB interface to connect to either company’s higher-end (Virtex or Stratix) FPGAs. Atmel says that the CAP7E can also be adapted to work with most of Lattice’s FPGA series as well.
Should your application require a more powerful RISC engine, there is an FPGA-friendly version of the ARM9 processor available as well as a metal-programmable companion device. Known as the CAP9E, it’s been available for a little while but it’s not been heavily publicized. See the pricing and availability section at the end of this review for links to more information on these processors.
So, just what could do with a bunch of programmable logic (either as an FPGA or an integrated gate array) attached to one of the most popular RISC cores in the industry? The mind boggles at the kinds of fun stuff that you might do with the CAP7E but a short list might include making it into a really fast, custom digital signal controller, using it as a display controller to drive real-time 2-way interfaces and, of all things, using it as the heart of high-precision GPS systems. Although there are lots of stand-alone GPS chips that are more than good enough for getting you and the family minivan from Nutley to Van Nuys, most applications in the industrial and commercial realms need better precision and performance under degraded conditions than commercial products can supply. Atmel says that some of the early interest in the CAP7E came from folks who wanted to quickly build their own custom high-precision correlators without the cost of an ASIC.
I agree with Atmel that an ARM7 core equipped with custom PWM logic might also have lots of potential applications as a high-efficiency motor controller although I think they will have some significant competition here from the incumbent players like TI, IR, Freescale and Microchip.
Atmel's plans to offer the tools to embed multiple copies (up to 10) versions of their AVR microcontroller soft cores in the FPGA or metal-programmable area seem a bit odd at first glance, but could make sense in some applications which require multiple real-time control functions. For example, they see great potential for cutting parts count and BOM cost in robotics, where a single ARM-based chip might have a half-dozen or more PICs aboard, each running its own joint or drive wheel.
Atmel AT91CAP7E is available now and is priced at $9.50 in 10-k piece lots in BGA-225. The AT91CAP7X development kit is priced at $3500 (unless you can convince Atmel that you are serious about working with them). Look for a simpler sub-$500 development kit that uses smaller FPGAs some time later in 2008.
AT91CAP Home Page
CAP7 and CAP9 Development Boards
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