A digital signal processor (DSP) is a specialized microprocessor designed specifically for digital signal processing, generally in real-time. DSPs can also be used to perform general-purpose computation, but they are not optimised for this function.

Rather than general computations, DSPs usually have an instruction set (ISA) optimised for the task of rapid signal processing, often using the following techniques:

• Multiply-accumulate (MAC) operations (good for all kinds of matrix operations, and especially convolution for filtering). Single cycle MAC is an assumption in many DSPs, thus alot of the following properties are derived (esp. Harvard architecture pipelining)
• Deep pipelining.
• The ability to act as a direct memory access device for the host environment.
• Saturation arithmetic, in which operations that produce overflows will accumulate at the maximum (or minimum) values that the register can hold rather than wrapping around (maximum+1 doesn't equal minimum as in many general-purpose CPUs, instead it stays at maximum). Sometime various sticky bits operation modes are availiable.
• Separate program and data memories (Harvard architecture).
• Most DSPs are fixed-point, because in real world signal processing, extra precision is often not required, and there is a large speed benefit; however, floating point DSPs are common for scientific and other applications where precision is required.
• Specialized instructions for modulo addressing in ring buffers and bit-reversed addressing mode for FFT cross-referencing.

Generally, DSPs are dedicated integrated circuits, however DSP functionality can also be realised using Field Programmable Gate Array chips. Present-day general-purpose microprocessors also have ideas and influences from digital signal processors, such as the MMX extensions in the Intel IA-32 architecture.

History

In 1978, Intel released the 2920 as an "analog signal processor". It had an on-chip ADC/DAC with an internal signal processor, but it didn't have a hardware multiplier and was not successful in the market. In 1979, AMI released the S2811. It was designed as a microprocessor peripheral, and it had to be initialized by the host. The S2811 was likewise not successful in the market.

In 1979, Bell Labs introduced the first single chip Digital Signal Processor (DSP), the Mac 4 Microprocessor. Then, in 1980 the first stand-alone, complete DSPs -- the NEC µPD7720 and AT&T DSP1 -- were presented at the IEEE International Solid-State Circuits Conference '80. Both processors were inspired by the research in PSTN telecomunications.

The first DSP produced by Texas Instruments (TI), the TMS32010 presented in 1983, proved to be an even bigger success, and TI is now the market leader in general purpose DSPs. Another very successful design was the Motorola 56000, but they were not as successful with follow-up models and today are no longer a leader in this market.

External links

• Microcontroller.com
• DSP Engineering Magazine (http://www.dspengineering.com)
• Bores D.S. Processor tutorial (http://www.bores.com/courses/intro/chips/index.htm)
• Texas Instruments Homepage (http://www.ti.com)
• DSP Discussion Groups (http://www.dsprelated.com)