Direct Memory Ac ccess s transfers a block of data directly to or from memory Issue Read CI→DMA An interrupt is sent when the block command Do something to 1A module else task is complete Read status o The processor is only involved at --Intern Of dma the beginning and end of the module DMA→CP transfer Next instruction (c)Direct memory access DEVICE MANAGEMENT
DEVICE MANAGEMENT Direct Memory Access ❖Transfers a block of data directly to or from memory ❖An interrupt is sent when the task is complete ❖The processor is only involved at the beginning and end of the transfer
Evolution of the vo Function o Processor directly controls a peripheral device Controller or vo module is added s Processor uses programmed 1O without interrupts s Processor does not need to handle details of external devices DEVICE MANAGEMENT
DEVICE MANAGEMENT Evolution of the I/O Function ❖Processor directly controls a peripheral device ❖Controller or I/O module is added ٭ Processor uses programmed I/O without interrupts ٭ Processor does not need to handle details of external devices
Evolution of the vo Function Controller or 1O module with interrupts s Processor does not spend time waiting for an vo operation to be performed ☆ Direct Memory Access Blocks of data are moved into memory without involving the processor s Processor involved at beginning and end only DEVICE MANAGEMENT
DEVICE MANAGEMENT Evolution of the I/O Function ❖Controller or I/O module with interrupts ٭ Processor does not spend time waiting for an I/O operation to be performed ❖Direct Memory Access ٭ Blocks of data are moved into memory without involving the processor ٭ Processor involved at beginning and end only
Evolution of the vo Function ☆Ⅳ o channel 10 module is a separate processor. Its with a pecialized instruction set tailored(造合)for VO 1O processor 1/0 module has its own local memory Its a computer in its own right DEVICE MANAGEMENT
DEVICE MANAGEMENT Evolution of the I/O Function ❖I/O channel ٭ I/O module is a separate processor. Its with a specialized instruction set tailored(适合) for I/O. ❖I/O processor ٭ I/O module has its own local memory ٭ Its a computer in its own right
Direct Memory Ac ccess s Takes control of the system from the cpu to transfer data to and from memory over the system bus Cycle stealing is used to transfer data on the ystem bus g The instruction cycle is suspended so data can be transferred The cpu pauses one bus cycle No interrupts occur while cycle stealing Do not save context DEVICE MANAGEMENT
DEVICE MANAGEMENT Direct Memory Access ❖Takes control of the system from the CPU to transfer data to and from memory over the system bus ❖Cycle stealing is used to transfer data on the system bus ❖The instruction cycle is suspended so data can be transferred ❖The CPU pauses one bus cycle ❖No interrupts occur while cycle stealing ٭ Do not save context