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The launch of a new DSP family shows there's life in the old dog yet

Flick back through the virtual pages of the New Electronics website and you'll see articles discussing when, rather than if, the digital signal processor would disappear.

To the bystander, it seemed that DSPs were under growing pressure from two directions. On one side, pressure was being applied by FPGA suppliers, who were beginning to include dedicated DSP functionality in their increasingly capable devices. On the other side were microcontrollers and microprocessors. Even in the late 1990s, instructions were being added to
Intel's Pentium processor that allowed some form of DSP to be undertaken. The more recent rise of ARM based microcontrollers – the Cortex-M4 core, for example, is optimised for DSP – as well as devices like Microchip's dsPIC digital signal controller family, increased the pressure. It was only a matter of time, you might have thought.

Yet, more than a decade since the discussion started, DSPs are still with us. Underlining that fact is the recent launch by Analog Devices of the latest family of Blackfin processors. This isn't just the filling out of a previously announced road map; it's a new family built around an updated processing core – Blackfin+.

Andrew Lanfear, product marketing manager with Analog Devices, noted: "The ADSP-BF70x series features performance leading devices. Designers have the choice of either getting double the performance of competitive devices for the same power consumption or getting the same performance for half the power. In launching this range, we have looked to meet an increasing need for cost effective real time processing in such applications as machine intelligence and real time imaging."

The Blackfin+ core features two 16bit multipliers, one 32bit multiplier and two 40bit accumulators, which can be used together as a 72bit accumulator. It can perform two 16 x 16 MACs or one 32bit MAC in each cycle. Signed and unsigned formats, rounding, saturation and complex multiplies are supported.



Lanfear believes single cycle 32bit processing is an important feature of the new family. "It's important to offer this to handle, for example, fast Fourier transforms." According to Analog, the Blackfin+ core performs a complex 16bit fast Fourier transform 30% faster than the previous core due to maths improvements.

The company adds that the ALUs can perform a traditional set of arithmetic and logical operations on 16 or 32bit data. In addition, a range of special instructions is included to accelerate various signal processing tasks. A set of video instructions includes byte alignment and packing operations, 16bit and 8bit adds with clipping, 8bit average operations and 8bit subtract/absolute value/accumulate (SAA) operations.

Lanfear pointed to this particular need as a reason for selecting a DSP, rather than an FPGA or a microcontroller. "We're hearing from our customers that an ARM based microcontroller doesn't solve all their real time DSP requirements. One of the issues is that ARM's cores work with a multilevel cache and this can impact the microcontroller's deterministic performance."

In his opinion, customers want cost effective real time processing, coupled with low power consumption and higher levels of system integration. He pointed to such parameters as low latency, deterministic performance, access to low power 32bit processing and glueless peripheral connectivity.

"We're delivering a processor that has right integration and right peripherals," he said, "which can replace what was an ASSP type product."

He doesn't discount the FPGA approach, but noted: "When we look at the FPGA market, we're aware of devices such as Xilinx' Zynq. Our contention is that, in the BF70x family, we're offering a range of products with the performance that meets the application requirements of our customers."

He believes power consumption is one reason why a DSP might be specified, rather than an FPGA. "The BF70x range will consume less than 100mW," he continued. "Most FPGAs will struggle to match this."

With a set of system peripherals and memory options, the Blackfin processor is said by Analog Devices to be the platform of choice for applications that require RISC-like programmability, along with multimedia support signal processing in one package.

Lanfear contended: "General purpose DSP is hard to do and the features we have included target the BF70x family at wide range of applications." Potential applications are said to be found in a range of markets, including automotive systems, instrumentation and power and motor control. He added: "Because of the family's feature set, the parts are finding their way into applications in the military, automotive and audio sectors, which weren't the original targets."

One particular application for DSPs in the automotive sector, said Lanfear, is in noise cancellation. "With noise cancellation, it's quieter inside the car. That means the manufacturer doesn't need to include as much noise insulation as would have been needed, so the car is lighter and cheaper to build."

There are eight members in the BF70x family's road map, with two packaging options – an 88lead LFCSP or a 184ball CSP BGA, both measuring 12 x 12mm. At the entry level are the BF700 (LFCSP) and the BF701 (BGA), both running at a maximum of 200MHz and with 128kbyte of L2 SRAM. The remaining six devices – three in each packaging option – have a maximum clock rate of 400MHz and come with 256k, 512 or 1Mbyte of SRAM. All eight parts have 136kbyte of L1 SRAM and 512kbyte of L2 ROM.

Lanfear said the provision of up to 1Mbyte of SRAM on chip removes the need for access to internal memory. However, should the application require, the devices in the BGA package feature an optional 16bit DDR2 memory interface.

The BF70x family will be manufactured on a 40nm process; the BF60x range which preceded it was designed for the 65nm node. "We are taking advantage of a process shrink,"
Lanfear admitted, "but we are also focusing on power efficiency. The core in each device is clocked at a maximum of 400MHz and that's more than enough for the applications which we have in mind. And the previous range had dual 400MHz cores, whereas the BF70x family features just one 400MHz core drawing less than 100mW."

Analog Devices has also responded to what it perceives as growing demand for more security. There's an onboard cryptographic hardware accelerator that features fast secure boot with decryption and authentication. Meanwhile, for always on safety critical applications, the BF70x series also provides high data integrity with parity and error correction code protected memory. "Security features are important," said Lanfear, "as customers want to ensure they can protect their IP." However, security features don't get in the way. "The BF70x range can do a 512kbyte secure boot with decrypt and authentication in less than 55ms," said Lanfear.

The BF70x range is supported by Analog's Crosscore integrated development environment and by the ADSP-BF707 EZ-KIT-Lite development board. Also available is the Blackfin Low Power Imaging Platform – or BLIP – as well as a range of software modules and video and audio codecs.

Samples of the new DSP family are available now, with volume production scheduled for Q3 2015.

Author
Graham Pitcher

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