Chapter 4 Computer Organization

1. Chapter 4Computer Organization Vishal Shah Vishal Pinto

2. Contents • The Von Neumann Architecture • The Central Processing Unit • The Primary Memory • I/O devices • Interrupts • Conventional Contemporary Computers • Mobile Computers • Multiprocessors and Parallel Computers

3. Interrupts Why Device Drivers? read ( devID, myData, dataLength ); x = f ( myData, dataLength, …)

4. Software … // Start the device … while ((busy = = 1) || ( done = = 1)) wait( ); //Device I/O complete … done = 0; Hardware busy done … while (( busy = = 0) && (done = = 1)) wait( ); // Do the I/O operation busy = 1; …

5. I/O Polling A process in which a number of I/O devices are interrogated, one at a time, to determine if service is required. Introduces Busy-wait situation.

6. CPU InterruptRequest flag . . . Device Device . . . Device Detecting an Interrupt

7. Fetch-Execute cycle with an Interrupt while (haltFlag not set during execution) { IR = memory[PC]; PC = PC + 1; execute (IR); if ( InterruptRequest) { memory[0] = PC; PC = memory [1]; } } Conceptually ,hardware connects all device-done flags to the interrupt request flag using inclusive-OR logic

8. The Interrupt handler Interrupt_Handler { SaveProcessorState( ); for ( i = 0; i<Number_of_devices; i++) if (device[i].done = = 1) goto device_handle(i); /* Something wrong if we get here }

9. Extension to detect interrupt more rapidly? Interrupt vector. • Race condition ? Interrupt occurs while the Interrupt handler is in the midst of execution. Solution: Avoid it.

10. Disabling Interrupts If ( InterruptRequest && InterruptEnabled ) { /* Interrupt current process */ disableInterrupts ( ); memory [0] = PC; PC = memory[1]; }

11. Mode S 1 2 trap 3 Trusted Code User Supervisor Trap Instruction Used by a process running in user mode that wants to perform an operation that requires privileged instructions

12. ALU CU Address Bus Data Bus Primary Memory Unit Device Controller Device Von Neumann Architecture CPU

13. RAM ROM Boot Prog Power UP POST Loader BIOS OS CMOS Boot Device Bootstrapping the Machine

14. Boot Loader Program Fixed_LOC:// Bootstrap loader entry point load R1, =0 load R2, =LENGTH_OF_TARGET /*The next instruction is really more like a procedure call than a machine instruction. It copies a block from BOOT_DISK to BUFFER_ADDRESS.*/ read BOOT_DISK, BUFFER_ADDRESS Loop: load R3, [BUFFER_ADDRESS, R1] store R3,[FIXED_DEST, R1] incr R1 bleq R1, R2, loop br FIXED_DEST

15. Mobile Computers Features: • Physically light and small • Severely constrained in the rate at which it can consume power • O/P devices are small and usually is speaker • Does not contain a storage device • Has removable devices like CF cards, NIC..

16. System-on-chip Technology Set of memory and device functions that is needed by the onboard processor on a single chip.

17. Power Management • Notebook computers • Switch OFF LCD display • Power down Disks • Mobile computers • Switch OFF or dim displays • Reducing the clock speed of processor

18. Operand 1 Function Unit Result Operand 2 Multiprocessors and Parallel Computers • Parallel instruction Execution • Pipelined function unit Operand 1 Result Operand 2

19. ALU Control Unit ALU ALU Control Unit ALU ALU Conventional Architecture SIMD Architecture Array processors

20. Shared Memory Multiprocessors • Processors are Interconnected with one another with primary memory using specialized hardware • Popular among programmers tools used to develop s/w for single process could easily be used with the shared memory architecture • Distinct from Von Neumann architecture but rely upon it.

21. Distributed memory Multiprocessors • Collection of CPU’s with their memory interconnected using high-speed n/w • High speed LAN or High speed fiber optic n/w • Do not support ordinary sequential Programming languages like Shared memory machines do • Exchanges data as messages

22. Network of workstations • PC’s interconnected with a network • Usually individual computers with autonomous executing units with their own OS