Datapath design

6.

Gill, A., E. Corwin, and A. Logar. Assembly Language Programming for the 68000. Englewood Cliffs, NJ: Prentice-Hall, 1987.

7.

Goldberg, D. "What Every Computer Scientist Should Know about Floating-Point Arithmetic." ACM Computing Surveys, vol. 23 (March 1991) pp. 5-48.

8.

Hamming, R. W. Coding and Information Theory. 2nd ed. Englewood Cliffs, NJ: Prentice-Hall, 1986.

9.

IEEE Inc. IEEE Standard for Binary Floating-Point Arithmetic (ANSI/IEEE Std 7541985) New York, August 1985.

10.

Intel Corp. MC-8085 Family User's Manual. Santa Clara, CA, 1979.

11.

Kane, G. and J. Heinrich. MIPS RISC Architecture. Englewood Cliffs, NJ: Prentice-Hall, 1992.

12.

Motorola Inc. M68000 Family Programmer's Reference Manual. Phoenix, AZ, 1989.

13.

Myers, G. J. Advances in Computer Architecture. 2nd ed. New York: Wiley-Interscience, 1992.

14.

Patterson, D. A. and C.H. Sequin. "A VLSI RISC," IEEE Computer, vol. 15 (September 1982) pp. 8-21.

15.

Sieuwertz, D. P. and R. S. Swarz. Reliable Computer Systems. 2nd ed. Burlington, MA: Digital Press, 1992.

16.

van Someren A. and C. Atack. The ARM RISC Chip. Wokingham, England: Addison-Wesley, 1994.

CHAPTER 4

Datapath Design

An instruction-set processor consists of datapath (data processing) and control units. This chapter addresses the register-level design of the datapath unit, while Chapter 5 covers the control unit. The focus is on the arithmetic algorithms and circuits needed to process numerical data. These circuits are examined first for fixedpoint numbers (integers) and then for floating-point numbers. The use of pipelining to speed up data processing is also discussed.

The design of circuits to implement the four basic arithmetic instructions for fixedpoint numbers—addition, subtraction, multiplication, and division—is the main topic of this section. It also discusses the implementation of logic instructions and ALU design.

Add and subtract instructions for fixed-point binary numbers are found in the instruction set of every computer. In smaller machines such as microcontrollers they are the only available arithmetic instructions. As we have seen in earlier chapters, addition and subtraction hardware (Example 2.7) or software (Example 3.1) can be used to implement multiplication and, in fact, any arithmetic operation. Beginning with Charles Babbage, computer designers have devoted considerable effort to the design of high-speed adders and subtracters. As we will see, these basic circuits can be designed in many different ways that involve various tradeoffs between operating speed and hardware cost.

223

6. Gill, A., E. Corwin, and A. Logar. Assembly Language Programming for the 68000. Englewood Cliffs, NJ: Prentice-Hall, 1987.

7. Goldberg, D. "What Every Computer Scientist Should Know about Floating-Point Arithmetic." ACM Computing Surveys, vol. 23 (March 1991) pp. 5-48.

8. Hamming, R. W. Coding and Information Theory. 2nd ed. Englewood Cliffs, NJ: Prentice-Hall, 1986.

9. IEEE, Inc. IEEE Standard for Binary Floating-Point Arithmetic (ANSI/IEEE Std 754-1985) New York, August 1985.

10. Intel Corp. MC6805 Family User's Manual. Santa Clara, CA, 1979.

11. Kane, G. and J. Heinrich. MIPS RISC Architecture. Englewood Cliffs, NJ: Prentice-Hall, 1992.

12. Motorola Inc. MC68000 Family Programmer's Reference Manual. Phoenix, AZ, 1989.

13. Myers, G. J. Advances in Computer Architecture. 2nd ed. New York: Wiley- Inter-science, 1992.

14. Patterson, D. A. and C.H. Sequin. "A VLSI RISC." IEEE Computer, vol. 15 (September 1982) pp. 8-21.

15. Siewiorek, D. P. and R. S. Swarz. Reliable Computer Systems. 2nd ed. Burlington, MA: Digital Press, 1992.

16. van Someren A. and C. Atack. The ARM RISC Chip. Wokingham, England: Addison-Wesley, 1994.

CHAPTER 4

Datapath Design

An instruction-set processor consists of datapath (data processing) and control units. This chapter addresses the register-level design of the datapath unit, while Chapter 5 covers the control unit. The focus is on the arithmetic algorithms and circuits needed to process numerical data. These circuits are examined first for fixed-point numbers (integers) and then for floating-point numbers. The use of pipelining to speed up data processing is also discussed.

4.1 FIXED-POINT ARITHMETIC

The design of circuits to implement the four basic arithmetic instructions for fixed-point numbers—addition, subtraction, multiplication, and division—is the main topic of this section. It also discusses the implementation of logic instructions and ALU design.

4.1.1 Addition and Subtraction

Add and subtract instructions for fixed-point binary numbers are found in the instruction set of every computer. In smaller machines such as microcontrollers they are the only available arithmetic instructions. As we have seen in earlier chapters, addition and subtraction hardware (Example 2.7) or software (Example 3.1) can be used to implement multiplication and, in fact, any arithmetic operation. Beginning with Charles Babbage, computer designers have devoted considerable effort to the design of high-speed adders and subtracters. As we will see, these basic circuits can be designed in many different ways that involve various trade-offs between operating speed and hardware cost.

6. Gill, A., E. Corwin, and A. Logar. Assembly Language Programming for the 68000. Englewood Cliffs, NJ: Prentice-Hall, 1987.

7. Goldberg, D. “What Every Computer Scientist Should Know about Floating-Point Arithmetic.”