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The direct memory access or DMA mode of data transfer is the fastest amongst all the modes of data transfer.In this mode ,the device may transfer data directly to/from memory without any interference from the CPU.The device requests the CPU through a DMA controller to hold its data,address and control bus so that the device may transfer data directly to/from memory.
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Generally which transfer mode is faster DMA or PIO?
DMA transfers data directly from the drive to memory without involving the CPU. PIO involves the CPU and is slower than DMA mode.
Block diagram of 8257 dma controller?
it is a device to transfer the data directly between io device and memory without through the cpu so it performs a high-speed data transfer between memory and io device
What is burst mode and cycle stealing mode?
The DMA controller can be used to steal memory cycles from the processor. Hence this interweaing technique is called cycle stealing The DMA Controller may be Given exclusive access main memory to transfer the block of data without interruption this is known as block or burst mode
What is DMA structure?
Using interrupts driven device drivers to transfer data to or from hardware devices works well when the amount of data is reasonably low. For example a 9600 baud modem can transfer approximately one character every millisecond ( 'th second). If the interrupt latency, the amount of time that it takes between the hardware device raising the interrupt and the device driver's interrupt handling routine being called, is low (say 2 milliseconds) then the overall system impact of the data transfer is very low. The 9600 baud modem data transfer would only take 0.002% of the CPU's processing time. For high speed devices, such as hard disk controllers or ethernet devices the data transfer rate is a lot higher. A SCSI device can transfer up to 40 Mbytes of information per second. Direct Memory Access, or DMA, was invented to solve this problem. A DMA controller allows devices to transfer data to or from the system's memory without the intervention of the processor. A PC's ISA DMA controller has 8 DMA channels of which 7 are available for use by the device drivers. Each DMA channel has associated with it a 16 bit address register and a 16 bit count register. To initiate a data transfer the device driver sets up the DMA channel's address and count registers together with the direction of the data transfer, read or write. It then tells the device that it may start the DMA when it wishes. When the transfer is complete the device interrupts the PC. Whilst the transfer is taking place the CPU is free to do other things. Device drivers have to be careful when using DMA. First of all the DMA controller knows nothing of virtual memory, it only has access to the physical memory in the system. Therefore the memory that is being DMA'd to or from must be a contiguous block of physical memory. This means that you cannot DMA directly into the virtual address space of a process. You can however lock the processes physical pages into memory, preventing them from being swapped out to the swap device during a DMA operation. Secondly, the DMA controller cannot access the whole of physical memory. The DMA channel's address register represents the first 16 bits of the DMA address, the next 8 bits come from the page register. This means that DMA requests are limited to the bottom 16 Mbytes of memory. DMA channels are scarse resources, there are only 7 of them, and they cannot be shared between device drivers. Just like interrupts the device driver must be able to work out which DMA channel it should use. Like interrupts, some devices have a fixed DMA channel. The floppy device, for example, always uses DMA channel 2. Sometimes the DMA channel for a device can be set by jumpers, a number of ethernet devices use this technique. The more flexible devices can be told (via their CSRs) which DMA channels to use and, in this case, the device driver can simple pick a free DMA channel to use. Linux tracks the usage of the DMA channels using a vector of dma_chan data structures (one per DMA channel). The dma_chan data structure contains just two fields, a pointer to a string describing the owner of the DMA channel and a flag indicating if the DMA channel is allocated or not. It is this vector of dma_chan data structures that is printed when you cat /proc/dma
What is dma in detail?
Direct memory access (DMA) is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit (CPU).Without DMA, when the CPU is using programmed input/output, it is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work. With DMA, the CPU initiates the transfer, does other operations while the transfer is in progress, and receives an interrupt from the DMA controller when the operation is done. This feature is useful any time the CPU cannot keep up with the rate of data transfer, or where the CPU needs to perform useful work while waiting for a relatively slow I/O data transfer. Many hardware systems use DMA, including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel. Similarly, a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time, allowing computation and data transfer to proceed in parallel.DMA can also be used for "memory to memory" copying or moving of data within memory.
3 types of DMA transfer modes?
· Block transfer DMA controller takes the bus control by CPU. CPU has no access to bus until the transfer is complete. During this time CPU can perform internal operations that do not need bus. This is a common and popular method with modern microprocessors. · Cycle stealing This is a word-by-word transfer based on CPU cycle stealing. When DMA steals a cycle, CPU is stopped completely for one cycle. Cycle stealing is not an interrupt. CPU pauses for just one machine cycle. This type of transfer takes a period of time. Some major steps of DMA cycle stealing in order to transfer data to and form memory are: · DMA needs control of the CPU · DMA must use the bus only when the CPU does not need it · CPU is suspended by DMA just before it needs to use the bus · CPU pauses for one bus cycle · DMA transfers one words and then returns the control to CPU · The overall effect is to cause the CPU to execute more slowly · Interleaved DMA. It is similar to block transfer technique, here DMA controller takes the control of system bus only when CPU is not using it. For example, performing an ALU operation or incrementing a counter. The data transfer by this kind of method takes a period of time.
Why do printers use DMA?
Using DMA transfer to send print data to the computer may help speed up printing.
What transfer mode can transmit data from a device to memory without involving the CPU?
DMA transfer mode
Is dma controller is processor or controller?
processor
Why Direct memory access has priority over the CPU when both request a memory transfer?
we can transfer data direct to and from memory without the need of the CPU. The transfer of data between a fast storage device such as magnetic disk and memory is often limited by the speed of the CPU. Removing the CPU from the path and letting the peripheral device manager the memory buses directly would improve the speed of transfer. This transfer technique is called direct memory access(DMA). During DMA transfer, the CPU is idle and has no control of the memory buses. A DMA controller takes over the buses to manage the transfer directly between the I/O device and memory. With Regards. Veer Thakur. Chandigarh.
Which transfer mode can transmit data from a device to memory without involving the cpu?
DMA
Is ide and dma the same thing?
No, IDE stands for Integrated Drive Electronics A hardware interface widely used to connect hard disks, optical discs and tape drives to a PC. Introduced in 1986 with 20MB of storage, capacities increased a thousandfold in less than two decades. Compared to the SCSI interface, IDE has been the more economical choice. (Direct Memory Access) Specialized circuitry or a dedicated microprocessor that transfers data from memory to memory without using the CPU. Although DMA may periodically steal cycles from the CPU, data are transferred much faster than using the CPU for every byte of transfer. On PCs, there are eight DMA channels commonly used as follows. Most sound cards are set to use DMA channel 1. See PIO mode. DMA Used for 0 8-bit transfer 1 8-bit transfer 2 Floppy disk controller 3 8-bit transfer 4 Cascaded from 0-3 5 16-bit transfer 6 16-bit transfer 7 16-bit transfer DMA Disk Transfers There are various modes of data transfer on IDE disk drives. The PIO modes use the CPU, and the DMA modes bypass the CPU.
