The selection of DSP and MCU

Recently, our company launched a new project, the sensor analog signal acquisition, there are two requirements: 1.ad accuracy requirements of 16 bits 2. The sampling frequency is required to reach 2000HZ. It seems that many single-chip microcomputer, basically can not reach these two conditions, before using the Stm32 12-bit AD, sampling frequency can only be maintained at about 100.

DSP and single chip microcomputer

Single-chip microcomputer has realized the simple control function, temporarily satisfies the engineering design demand, but along with the computer science and technology, the signal processing theory and the method rapid development, to the engineering control or the signal processing chip real-time and the precision request is more and more high, in some fields, the low-grade monolithic processor already can no longer satisfy the request, This has led to the emergence and application of DSP with fast and high-precision processing capability .

A Features of DSP

1. operation Speed '

MIPS (millionsofinstructionspersecond : means DSP The number of instructions per second that can be processed, that is, DSP The greater the value, the DSP The faster the processing speed, the higher the speed of operation.

· mops (millionsofoperationspersecond : DSP usually operates in addition to including The operation also includes addressing, DMA Access data transfer, i / o operations and so on, so you need to look at the contents of the operation, but in general, Span style= "Font-family:calibri" >mops mops can be DSP Overall performance of the chip is described comprehensively.

• Instruction Cycle: The time required to execute an instruction, usually in NS ( nanoseconds ) , such as tms320lc2406 at the frequency of The instruction period at 40MHz is 25ns.

2.shippedCalculation accuracy.in general, floating-pointDSPthe operation accuracy of the chip is higher than the fixed pointDSPprecision of the operation of the chip. General PointDSPthe word length of the chip is -Bits, -bit or +bit, the word length of the floating-point chip is +bit. Accumulators are generally +bit or +bit. Fixed pointDSPis characterized by high frequency, fast speed, low cost, small power consumption, mainly used in high complexity control, communication, voice/image, consumer electronics and other fields, and floating-pointDSPmainly used in complex image, speech, pattern recognition and other fields。

3. Word length word size is an important factor affecting the cost, because it directly affects the size of the chip, the number of pins and the size of the memory. When the design meets the performance index, the chip with the smallest data word should be chosen as far as possible. 4. Memory and other on-chip hardware resource memory and other on-chip hardware resources mainly include the size of the memory, the number of on-chip memory, bus addressing space and the number of external interfaces can be provided.

5. Development Debugging tools simple and practical, powerful development debugging tools and related supporting software, technical documentation is the development of large and complex DSP system necessary conditions, to shorten the product development cycle has a very important role. The development of debugging tools consists of two parts: software and hardware. 6. Power and power management in some products that have special requirements for power consumption, such as personal digital products, portable devices and outdoor equipment, power consumption and power management specifications have a direct impact on the model selection of the DSP chip. In addition, many DSP Strengthen the management of power supply, usually with sleep, wait mode and other ways to save power consumption, expect to achieve low power consumption. Many of TI 's chips offer this functionality and provide detailed application notes that can be implemented with a simple hardware configuration or a corresponding register of software configurations.

Two The characteristics of single-chip microcomputer

Single-chip microcomputer, refers to a chip on the integration ofCPU,RAM,ROM (EPRoMorEEPROM), clock, Timer/counter, multifunction serial or parallelI/Ogeneral of the mouthIC, such asIntelCompany's8031,8051and later.at89c51and so on. In addition to having the above basic functions, some single-chip microcomputer is also integrated withA/D,D/A, such asIntelCompany's8098series and so on. Generally speaking, monolithic microcomputer generally has the following characteristics.

• Ability to handle bits.

• Predictable execution cycle.

• Specializes in interrupt handling, especially for external asynchronous events.

• Rich I/0 function.

• Low price for easy development.

SCM After many years of development, the development of a complete environment, the development of tools, the application of a large number of talent, adequate reserve.

Three Advantages of DSP

Compared with MCU,DSP devices generally have higher integration, faster CPU, higher capacity memory, built-in baud rate generator and FIFO Buffer, also provides high-speed synchronous serial port and standard asynchronous serial port, some also integrated a/D sampling circuit, for the control domain DSP also provides multi-channel PWM output for motor control to reduce developer workload. DSP devices generally employ an improved Harvard architecture, with independent programs and data spaces that allow simultaneous access to programs and data. Built-in high-speed hardware multiplier and enhanced multi-level pipeline, so that DSP devices with high-speed data computing capabilities.

Dspcan be compared with some upscale -bit single-chip microcomputer single instruction execution cycle is reduced8~Tentimes, can be completed in one cycle by adding operations, faster than the single-chip computer operation -~ -Times,Can greatly improve the existence of many multiply-add operationsFFT (Fast Fourier transform)and the operation speed of the filter. In addition,DSPThe device also providesJTAGinterface, with more advanced development means, production testing more convenient, development tools to achieve full-space transparent simulation, users can see all storage empty ask orI/Ospace changes without consuming any resources from the user. Development software with assembly/linkCcompiler,CThe source debugger and so on, so that users do not have to worry about compiling details, so you can focus more on algorithmic design and program development. In conclusion,DSPis to meet the digital signal processing, control the development of a class of specialized microprocessor, generally has the following characteristics.

• With an improved Harvard bus structure, there are two internal buses, the data bus and the program bus. The application of the program and data space structure, respectively, have their own address bus and data bus, you can complete the operation of the command and operation.

• Using pipelining, each instruction is divided into a number of steps, such as taking instruction, decoding, fetching number, execution, etc., which are completed by several functional units on the chip, and support the parallel processing of tasks.

• Achieve one or more multiply -accumulate (MAC) operations in one instruction cycle , saving computational time.

• Integrates multiple address generation units, supports special instructions such as loop addressing and bit reverse order, and realizesaddressing and sequencing in FFT, convolution and other operations, making the computation speed greatly improved.

• One or more sets of independent DMA control logic to increase the throughput bandwidth of the data, providing protection for high-speed data exchange and digital signal processing.

• Supports repetitive operations and avoids excessive time spent in cyclic operations.

• Rich on-chip memory and external expansion memory interface.

• Provide multiple serial or parallel i / o interface and special i / o interface ( etc )

Because the MCU and DSP have their own characteristics , so they have different fields of application. General microcontroller is often used in some simple control areas, these applications generally do not require a high precision and digital signal processing, and in some high-precision control areas, especially the need for a variety of sensor signal processing occasions, the application ofDSP more. Therefore, it is not simple to evaluate whether the microcontroller is better or better , but should be based on different engineering needs, choose the right, cost-effective processor. Chapter 1 Introduction to the field of control, especially the need for a variety of sensor signal processing occasions,the application ofDSP more. Therefore, it is not simple to evaluate whether the microcontroller is better or better , but should be based on different engineering needs, choose the right, cost-effective processor.

The selection of DSP and MCU