TI rolls out DSP for embedded control apps

TI rolls out DSP for embedded control apps
By Charles J. Murray and Patrick Mannion, EE Times
September 5, 2001 (11:14 a.m. EST)
URL: http://www.eetimes.com/story/OEG20010905S0034

PARK RIDGE, Ill. — Texas Instruments has rolled out a digital signal processor core designed for tighter control of products ranging from industrial drives and optical networks to automotive power steering systems.

TI engineers claim the C28X is 12 times speedier than the next fastest 32-bit DSPs, its own C24X series, which operates at less than 40 Mips, and Motorola's DSP56F800, with speeds comparable to those of the TI C24X platform.

With a top speed of 400 million instructions per second (Mips) and its specially designed architecture and software, the C28X is being touted as the strongest DSP candidate yet for embedded control applications, many of which now use analog techniques or microcontrollers.

"For embedded engineers, the No. 1 function has always been control," said Paul Zorfass, senior analyst for IDC/FTI (Framingham, Mass.). "This family of DSPs is a tight response to that market. It's very specifically tuned for control ne eds."

TI engineers said the DSP's additional processing power will make it possible for electric motors to operate at variable speeds in factory automation equipment, home appliances, electric vehicles and myriad other applications. Using such variable-speed techniques, next-generation motors could vary their speed to fit the conditions. Blower motors in air conditioners and refrigerators, for example, could run more slowly when needed, thus saving energy. Until now, electric motors in those applications have operated on an on-off, single-speed basis.

"There's a trend among the old-line equipment makers to move from analog- or microprocessor-based solutions to DSP-based solutions," said Scott Roller, C2000 platform marketing manager for Texas Instruments. "This lets them do that, because it also incorporates some features usually only found in microcontrollers."

Tighter control could also benefit hard disk drives, which could achieve higher numbers of tracks per inch for higher storage density. I n automation applications, the higher performance of the new DSP family could be used to ascertain motor torque in real-time or to eliminate certain feedback sensors in motion control.

The higher speed and better control was achieved chiefly through the DSP's architecture. While DSPs are by design well-suited to the math-intensive control algorithms needed for complex control functions, they fall short when it comes to interrupt handling and timers. To compensate for the shortcoming, TI added interrupt management and 32-bit timers to the C28X's 32 x 32 single-cycle multiply-accumulate (MAC), a JTAG serial interface and 32-bit register file.

TI said it achieved the leap in speed with architecture enhancements. Of the three 32-bit timers in the core, two are dedicated to the real-time operating system, the third dedicated to general-purpose computing. Engineers also modified the arithmetic logic unit (ALU) to use a "read-modif-write atomic" architecture, in which the "atomic" portion handles logic ope rations and bit manipulation. As a result, the system gains efficiencies in code size and execution times.

The extended addressing feature supports up to 8 Mbytes of program memory and 8 Gbytes of data, providing greater support for control procedures.

Peripheral support includes a host of serial and parallel control interfaces, as well as a specially designed flash memory structure. The C2812 supports 128 kwords of flash memory and 18 kwords of RAM, with a unified architecture so code can be run out of each.

"Historically," said Roller, "the fastest access time [for flash] was on the order of 1 MHz. However, with our sophisticated prefetch buffering mechanism, we can get on the order of 110 or 120 Mips."

Other features include 128-bit code security and the addition of a controller area network (CAN) interface. The 12-bit A/D has conversion times on the order of 200 ns, with a continuous throughput of 16.7 MSamples/second. "Many customers have a need to sample two signals simultaneously," sa id Roller, "so we support that with dual sample and hold."

But for some control engineers, hardware performance may be less important than the ability to program in a C-language. "Assembly language is more difficult to maintain and it's less portable," Zorfass said. "In C language, engineers can develop more rapidly and bring other software tools to bear."

TI's new DSP is said to have enough headroom to allow high performance even when using C/C++ compilers. "If you throw 150 Mips at a solution, the raw Mips alone will allow you to stay in a high-level language," Roller said.

The new DSP family could also help usher in electric power steering systems, displacing conventional hydraulic methods. Until now, computing power has limited the production of electric steering systems, Roller said.

"To do electric power steering requires a fairly sophisticated control algorithm, because you have to make sure the electric motor applies a precise amount of torque," he said.

The software also include s a library for laser-specific functions, including temperature control, intensity control and current/voltage control. "While tunable lasers and motor control may seem like polar opposites in terms of applications, the control problem they try to solve is very similar," Roller said.

Texas Instruments said it plans to roll out samples of the new DSP core in the first quarter of 2002 and will go into production in the second quarter. Pricing per unit in quantities of 10,000 is expected to be $17.95 for the F2810 (64 kwords of embedded flash) and $22.95 for the F2812 (128 kwords.)