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DMA allows devices to communicate with each other directly, instead of relying on the CPU to manage the transfers. This frees the CPU up to do other tasks, and increases system performance.
Wiki User
∙ 15y ago
Wiki User
∙ 12y agovishnu
without dma, when the cpu without programmed input/output.
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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.
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
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 DMA controller data transfer is faster?
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.
Which transfer mode can transmit data from a device to memory without involving the cpu?
DMA
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.
What is the two data transfer modes used in hard drives?
DMA (Direct Memory Access) or PIO (Programmed Input/Output) Transfer Modes. DMA transfers data to memory without use of the CPU. PIO involves CPU and is slower.ASCII & Binary
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.
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 are types of DMA?
DMA is a mechanism through which a hardware device can transfer data to or from memory without using the processor. The processor is required to set up the transfer, and the device will signal the processor when it has completed the transfer. The advantage of this system is that the processor can perform other tasks while the DMA transfer is being performed. There are several types of DMA used in Windows 2000 and later: ; Common-buffer DMA : Common-buffer DMA is performed when the system can allocate a single buffer that is accessible by both the hardware and the software. The driver is responsible for synchronizing accesses to the buffer. The memory is not cached, making this synchronization easier for the driver. After setting up a common buffer, both the driver and the hardware can write directly to the addresses in the buffer without any intervention from the HAL. ; Packet DMA : Packet DMA is performed when there is a single existing buffer that must be mapped for use by the hardware. An example of using packet DMA is the transfer of a file from memory to a disk. Using common-buffer DMA in this situation would be wasteful, because the file would have to be transferred to the common buffer before the hardware could transfer it to the disk. Instead, the HAL is consulted; it gives the driver the information it needs to help the hardware find the actual buffer in memory. This operation is complicated by the need for the routines involved to work across different architectures. ; Scatter/gather DMA : Scatter/gather DMA is a shortcut method that sets up several packet DMA transfers at once. If you are transferring a packet over the network, for example, each part of the network stack adds its own header (TCP, IP, Ethernet, and so forth). These headers are all allocated from different places in memory. In this case, the scatter/gather DMA saves time by issuing a batch request to the HAL to map each header plus the data segment for access by the hardware. Instead of having to call the packet DMA routines on each part of the packet, this method calls each routine once, and lets the HAL be responsible for mapping each one individually. Note Scatter/gather capability does not mean that the device can use the scatter/gather routines. Scatter/gather capability refers to a flag in the device description that indicates that the device is able to read or write from any area in memory, instead of just a certain range. ; System DMA : System DMA is performed by programming the system DMA controller on the motherboard to do the transfer directly. Only ISA cards can use system DMA.
What is busmastering?
bus mastering is a feature supported by many bus architectures that enables a device connected to the bus to initiate transactions. Also called "First-party DMA", to contrast it with Third-party DMA, the situation where the system DMA controller is actually doing the transfer.
