8086/8088-BASED MULTIPROCESSING SYSTEMS

• Multiprocessor Systems refer to the use of multiple processors that execute instructions simultaneously and communicate using mailboxes and semaphores
• Maximum mode of 8086 is designed to implement3basic multiprocessor configurations:
• coprocessor (8087)
• closely coupled (dedeicated I/O processor:8089)
• loosely coupled (Multibus)
• Coprocessors and closely coupled configurations are similar-both the CPU and the external processor share:
  • Memory
  • I/O system
  • Bus&bus control logic
  • Clock generator

Coprocessor Configuration

• WAIT instruction=allows the processor to synchronize itself with external hardware, eg., waiting for 8087 math co-processor.
• When the CPU executes WAIT=waiting state.

• TEST input is asserted (low), the waiting state is completed and axecution will resume.

• ESC instruction: ESC opcode, operand opcode:immediate value recognizable toacoprocessor as an instruction opcode operand: name ofaregister oramemory address (in any mode)

• When the CPU executes the ESC instruction, the processor accesses the memory operand by placing the address on the address bus.
• If a coprocessor is configured to share the system bus, it will recognize the ESC instruction and therefore will get the opcode and the operand.

Control Unit

• Control unit. To synchronize the operation of the coprocessor and the processer.
• This unit has a Control word and Status word and Data Buffer
• If instruction is an ESCape (coprocessor) instruction, the coprocessor executes it, if not the microprocessor executes.

Numeric Execution Unit

• This performs all operations that access and manipulate the numeric data in the coprocessor's registers.
• Numeric registers in NUE are 80 bits wide.
• NUE is able to perform arithmetic, logical and transcendental operations as well as supplyasmall number of mathematical constants from its on-chip ROM.
• Numeric data is routed into two parts ways a64 bit mantissa bus and a16 bit sign/exponent bus.