DSCs evolve to target a broader market

The concept of the DSC (digital signal controller) is almost a decade old now, and their DSP (digital signal processing) capabilities have come to a broad range of MCU (microcontroller) architectures. Moreover, DSCs have moved well beyond their power-centric heritage to address telephony, Internet, and multimedia applications.

DSCs are simply MCUs with added DSP functionality. In all fairness, the DSC designator is inexact and not even universally used by MCU makers. The DSC designation might mean that an MCU has been augmented with a single DSP-oriented feature such as a single-cycle MAC (multiply accumulate) unit that accelerates math functions. Some DSCs also add functions such as PWM (pulse width modulation) blocks or barrel shifters.

Among the most anticipated DSC developments is the ARM Cortex-M4 core, which ARM announced back in February. The architecture falls at the high end of the range of DSC implementations. The M4 design includes three MACs – a single-cycle 16- or 32-bit MAC and a separate pair of single-cycle 16-bit MACs. The architecture also supports SIMD (single-instruction multiple-data) arithmetic. For example, the architecture can handle four parallel 8-bit add or subtract operations in a single clock cycle. The M4 also integrates a floating-point unit.

ARM claims the M4 will deliver 1.25-DMIPS/MHz performance. M4 processors will target the motor-control and power-supply applications that originally prompted the DSC concept. But ARM identifies automotive, audio, and industrial automation as key targets.

Of course, ARM doesn’t make ICs but rather sells its IP (intellectual property) via licensing agreements. However, ARM cores have developed a large following as many companies have integrated the cores into products ranging from cell phone processors to ASSPs (application specific standard products) for network devices and multimedia products. Recently, companies such as STMicroelectronics have moved to ARM architectures for the bulk of their MCU lines.

The 2010 Embedded System Conference provided design engineers their first chance to see Cortex-M4 demonstrations based on real silicon. NXP Semiconductors was among the first licensees of the M4 architecture. The company has developed a 150-MHz DSC. The company has also developed a demonstration of the IC executing a seven-channel 32-bit audio graphic equalizer application. The demonstration reveals that the equalizer task only requires 12 MHz of the processor bandwidth. Without the DSC extensions, the same processor would spend about fourfold more time on the algorithm.

Let’s consider a few more DSC architectures to understand the range of capabilities of available options. Freescale Semiconductor has one of the broadest lines of DSCs, all of which are based on the 56800E core. The processor core includes three separate execution units that allow the processor to perform as many as six operations in each instruction cycle.

Freescale targets an especially broad array of applications with its DSCs. The Freescale website includes an application-specific view of the broad family broken into automotive, energy, industrial, medical, and motor-control segments. Consider the motor-control application. The MC56F8006 targets that application and integrates a single-cycle 16-bit MAC and four 36-bit accumulators. The DSC also includes a six-channel PWM block and dual 12-bit A/D converters.

Microchip Technology was the first to use the DSC term. Microchip’s newest DSCs are the members of the dsPIC334 GS family announced in March. The family directly targets digital power supplies. The family includes DSC with 12 to 18 1-ns PWM controllers that are common functions required in digital power control. The DSCs integrate 32 to 64 Kbytes of flash memory.

Microchip also offers design engineers an affordable way to experiment with DSC technology. The company offers the Explorer 16 development board, which integrates both a DSC and some Microchip MCUs. The board costs as little as $129, and a starter kit, with a complete IDE, costs around $300. The kit allows the user to work with the PIC32 MCU, the dsPIC33 DSC, and the PIC32MX MCU. You can add application-specific daughter cards such as a module that targets buck and boost power-supply topologies.