Direct Memory Access Data Count Data ines Data elster Address Register DMA Request DMA AcknowledGe Control Interrupt Read Figure 11.2 Typical DMA Block Diagram DEVICE MANAGEMENT
DEVICE MANAGEMENT Direct Memory Access
DMA The starting location in memory to read from or write to communicated on the data lines and stored by the dma module in its address register. A The number of words to be read or written, again communicated via the data lines and stored in the data count register DEVICE MANAGEMENT
DEVICE MANAGEMENT DMA ❖The Starting location in memory to read from or write to, communicated on the data lines and stored by the DMA module in its address register. ❖The number of words to be read or written, again communicated via the data lines and stored in the data count register
DMA and Interrupt breakpoint &The processor is suspended just before it needs to use the bus. The dma unit then transfers one word and returns control to the processor o Cycle stealing causes the cpu to execute more slowly. DEVICE MANAGEMENT
DEVICE MANAGEMENT DMA and Interrupt Breakpoint ❖The processor is suspended just before it needs to use the bus. The DMA unit then transfers one word and returns control to the processor. ❖Cycle stealing causes the CPU to execute more slowly
DMA and Interrupt Breakpoint Time Instruction Cvcle Processor Processor Processor Processor ProcessorProcessor Cycle Cvcle Cycle Cycle Cycle Cycle Fetch Decode Fetch Execute Store Process InstructionInstruction Operand Instruction Result Interrupt DMA Interrup Breakpoints Break point Figure 11.3 DMA and Interrupt Breakpoints During an Instruction Cycle DEVICE MANAGEMENT
DEVICE MANAGEMENT DMA and Interrupt Breakpoint
DMA o Number of required bus cycles can be cut by integrating the dma and lo functions Path between dma module and o module that does not include the system bus DEVICE MANAGEMENT
DEVICE MANAGEMENT DMA ❖Number of required bus cycles can be cut by integrating the DMA and I/O functions ❖Path between DMA module and I/O module that does not include the system bus