Computers

1
Computers

• Internal Communication

2
Basic Computer System
Processor
ALU
CNTL
.....
I/O module
BUS
CONTROLLER
MAIN MEMORY
BUS
Memory
3
Local and Peripheral Bus
4
Bus Operation

• Transfer Quantity (word)
• Address bus
• Control bus
• Data bus
• Speed
• Clock speed

5
Controller
PROCESSOR
REGISTER
REGISTER
REGISTER
BUFFER
6
Controller Operation
CPU passes parameters into the registers
Controller transfers data into the card buffer
Card processor checks the CRC

Data is transferred from the buffer to the bus
PROCESSOR
PROCESSOR
PROCESSOR
REGISTER
VALUE
REGISTER
VALUE
REGISTER
VALUE
BUFFER
CRC
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
7
I/O Operations

• For the I/O device to communicate with the CPU,
  the designer includes additional registers in the
  CPU.

• I/O Address Register contains address of I/O
  device
• I/O Buffer Register contains the value to be
  transferred to/from the I/O device

8
I/O Registers
CONTROL
ARITHMETIC-LOGIC
300
PC
ACCUM
I/O Address
IR
I/O Buffer
PROGRAM
DATA
1940
0003
300
940
5941
301
0002
941
2941
302
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I/O Processing

• Programmed I/O
• Control
• Test
• Read/Write
• Interrupt Driven I/O
• Direct Memory Access

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1. Programmed I/O

• Issue an I/O request

• Wait until I/O finished

• Continue program

CPU is tied up checking the I/O device until the
response is ready.
Solution Interrupt Processing
11
2. Interrupt Processing

• Issue an I/O request
• Store program parameters
• Start another process
• Process interrupt
• Return to original process

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3. DMA

• Processor issues a request, then
• Goes about its business
• DMA module transfers the data, then
• Tells the processor

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Interrupt Processing
FETCH
EXECUTE
Start
Halt
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Interrupt Processing

• Issue an I/O request
• Store program parameters
• Start another process
• Process interrupt
• Return to original process

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Classes of Interrupts

• Program illegal program operations
• Timer scheduled special operations
• I/O device controller signals completion of
  operations or error
• Hardware Failure power failure, memory parity
  error, etc.

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Interrupt Request (IRQ) Registers
CONTROL
ARITHMETIC- LOGIC
300
PC
I/O Address
IRQ
ACCUM
IR
I/O Buffer
Stack Addr.
PROGRAM
DATA
1940
0003
300
940
5941
301
0002
941
2941
302
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Basic CPU Operation
FETCH
EXECUTE
INTERRUPT PROCESS
Start
Halt
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Interrupt Stack
STACK

• Add a CPU register stack pointer.
• Recognize interrupt
• Store register
• contents (push stack)
• Process interrupt
• Restore register
• contents (pop stack)

Base Address
PROGRAM COUNTER
INSTRUCTION REGISTER
ACCUMULATOR
Etc.
May also contain interim program values
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Data TransferInterrupt Driven I/O
MAIN MEMORY
T
A
A
D
BUFFER
CPU
CPU
CPU
CPU
CPU
CONTROLLER
DASD
20
Data TransferDirect Memory Access
MAIN MEMORY
T
A
A
D
BUFFER
CPU
CONTROLLER
CONTROLLER
CONTROLLER
CONTROLLER
CONTROLLER
DASD