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Topic: Direct memory access


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  Direct memory access - Encyclopedia, History, Geography and Biography
Direct memory access (DMA) allows certain hardware subsystems within a computer to access system memory for reading and/or writing independently of the CPU.
DMA is an essential feature of all modern computers, as it allows devices to transfer data without subjecting the CPU to a heavy overhead.
For so-called "third party" DMA, as is normally used with the ISA bus, the transfer is performed by a DMA controller which is typically part of the motherboard chipset.
www.arikah.net /encyclopedia/Direct_memory_access   (582 words)

  
 Direct memory access control apparatus - Patent 4455620
Upon receipt of a direct memory access request from the high speed input/output device 40, the central processing unit is placed in a floating state, in which it is not capable of communication with the memory.
The direct memory access controller 303 causes a high GRANT signal to be generated by the switch control circuit 405 in the same manner as the operation in the previously described READ state, whereby a low DGRNT signal is generated from the switch control circuit 405.
However, the direct memory access controller 303 is responsive to a fall of the clock pulse to check the direct memory access request signal DRQ from the second byte to the final byte.
www.freepatentsonline.com /4455620.html   (6311 words)

  
 Direct memory access control system with byte/word control of data bus - Patent 4271466
The bus switching unit is responsive to the direct memory access control unit for interfacing the memory to the common data bus in such a manner as to cause the data transfer to be of the desired format.
In the case of the DMA control unit 11 accessing the memory 2, there are the word-unit and the byte-unit data transfers as mentioned above and, for the control of these transfers, it is necessary that the DMA control unit 11 apply instructions to the bus switching unit 12 and the memory 2.
When the direct memory access (DMA) by byte transfer is designated, this bit designates the position of the byte to be transferred in one word, that is, which of the upper and lower byte sides is transferred.
www.freepatentsonline.com /4271466.html   (7939 words)

  
 DMA - Direct Memory Access   (Site not responding. Last check: 2007-10-22)
DMA - A technique for transferring data from main memory to a device without passing it through the CPU.
Usually a specified portion of memory is designated as an area to be used for direct memory access.
An alternative to DMA is the Programmed Input/Output (PIO) interface in which all data transmitted between devices goes through the processor.
bugclub.org /eric/memory/dma.html   (196 words)

  
 DMA ~ Direct Memory Access
The DMA is used to free the CPU from direct control of data transfer between the memory and the Input/Output (I/O) Peripherals by making use of Channels.
Direct memory access (DMA) channels are system pathways used by many devices to transfer information directly to and from memory.
The lines to access these extra DMA channels were placed on the second part of the AT slot that is used by 16-bit cards.
members.tripod.com /~Eagle_Planet/dma__direct_memory_access.html   (1092 words)

  
 Direct Memory Access (DMA) Modes and Bus Mastering DMA
Direct memory access or DMA is the generic term used to refer to a transfer protocol where a peripheral device transfers information directly to or from memory, without the system processor being required to perform the transaction.
Since multiword DMA transfers are more efficient, and also have higher maximum transfer rates, single word DMA modes were quickly abandoned after ATA-2 was widely adopted--they were actually removed from the ATA standards in ATA-3.
So all DMA accesses today (including Ultra DMA) are actually multiword; the term "multiword" is now often assumed and no longer specifically mentioned.
www.storagereview.com /guide2000/ref/hdd/if/ide/modesDMA.html   (961 words)

  
 Introduction to direct memory access
Direct memory access (DMA) is a means of having a peripheral device control a processor's memory bus directly.
DMA permits the peripheral, such as a UART, to transfer data directly to or from memory without having each byte (or word) handled by the processor.
In burst mode, the DMA controller keeps control of the bus until all the data buffered by the requesting device has been transferred to memory (or when the output device buffer is full, if writing to a peripheral).
www.embedded.com /shared/printableArticle.jhtml?articleID=15300200   (1043 words)

  
 Direct memory access - Wikipedia, the free encyclopedia
For example, a PC's ISA DMA controller has 16 DMA channels of which 7 are available for use by the PC's CPU.
The ATA hard disk interface moved from programmed input/output (PIO) to direct memory access (DMA) only later in history.
DMA commanding in a PC is so expensive and dumb that it is not used for bit blit.
en.wikipedia.org /wiki/Direct_memory_access   (604 words)

  
 Direct Memory Access (DMA)
Direct Memory Access, or DMA, was invented to solve this problem.
Therefore the memory that is being DMA'd to or from must be a contiguous block of physical memory.
DMA channels are scarse resources, there are only 7 of them, and they cannot be shared between device drivers.
www.science.unitn.it /~fiorella/guidelinux/tlk/node87.html   (579 words)

  
 Direct Memory Access (DMA)   (Site not responding. Last check: 2007-10-22)
A perfect example of a device that's appropriate for DMA is a disk drive: data is on the device in nice regular-sized chunks (called sectors), and you always transfer a whole sector at a time between the device and memory.
When a device is ready to transfer a byte, it asks the DMA controller to do it for it; the DMA controller handles the bus handshaking and keeping track of the address to which the transfer should be made, while the device just reads or writes the bus's data lines.
The original PC had a DMA controller that would support four DMA channels (of which users were able to make use of three; channel 0 was dedicated to refreshing dynamic RAM); there are now two DMA controllers which can handle eight channels (though 0 and 3 are not usable by other devices).
www.cs.nmsu.edu /~pfeiffer/classes/473/notes/dma.html   (673 words)

  
 Direct Memory Access (DMA)
Thus the data flows from the I/O device to the CPU, and from the CPU to memory.
After all, these are lecture notes on "Direct Memory Access", so the idea is to access memory directly, and avoid the CPU as the middle man.
DMA (Direct Memory Access) is a way for I/O devices to bypass the CPU when accessing memory.
www.cs.umd.edu /class/spring2003/cmsc311/Notes/Memory/dma.html   (584 words)

  
 RFC 4297 (rfc4297) - Remote Direct Memory Access (RDMA) over IP Problem St   (Site not responding. Last check: 2007-10-22)
This is the means by which memory is exposed to the remote peer in an appropriate fashion, and the means by which the peer may access it, for instance, reading and writing.
Once associated, peer accesses to memory regions must be authenticated and made subject to authorization checks in the context of the association and connection on which they are to be performed, prior to any transfer operation or data being accessed.
Remote Direct Memory Access (RDMA) A method of accessing memory on a remote system in which the local system specifies the location of the data to be transferred.
www.faqs.org /rfcs/rfc4297.html   (5616 words)

  
 Direct Memory Access   (Site not responding. Last check: 2007-10-22)
IO <--> Memory is controlled by DMA unit.
DMA unit issues read and write cycles and is in control of the bus.
For block transfers DMA is far more efficient than interrupt driven IO.
www.cs.buffalo.edu /~bina/cse421/spring00/lec1/sld011.htm   (34 words)

  
 Direct Memory Access - Enable DMA - How To Enable DMA In Windows XP - Windows 98
When this DMA feature is enabled, it basically allows your Hard Drive and CD Rom Drive to transfer their information directly to and from memory without passing through the Microprocessor.
In short, when your disk drives use Direct Memory Access to access their information, this reduces the load placed upon your CPU and your system works faster.
Essentially, Direct Memory Access (DMA) is the theoretical data access rate of a Drive measured in megabytes per second.
www.real-knowledge.com /dma.htm   (1085 words)

  
 Eureka Technology - AMBA AHB Direct Memory Access (DMA) Controller IP core   (Site not responding. Last check: 2007-10-22)
The DMA controller then re-arbitrates for bus ownership to write data from the local buffer to the destination address on AHB bus.
Non-buffered DMA transfer is designed for transferring data between the AHB bus and the channel’s dedicated I/O port.
The DMA controller relinquishes the AHB bus and re-arbitrates for the bus again between each burst transfer so that other devices on the bus receive their fair share of memory bandwidth on the AHB bus.
www.eurekatech.com /products/arm/ep246.htm   (789 words)

  
 DMA (Direct Memory Access) Definition
Stands for "Direct Memory Access." DMA is a method of transferring data from the computer's RAM to another part of the computer without processing it using the CPU.
Ultra DMA hard drives use DMA to transfer data faster than previous hard drives that required the data to first be run through the CPU.
In order for devices to use direct memory access, they must be assigned to a DMA channel.
www.techterms.org /definition/dma   (238 words)

  
 Direct Access Storage Device (DASD) Direct Access Direct Memory Access (DMA)
Direct Access Storage Device (DASD): A storage device that can directly access data to be stored or retrieved, for example, a magnetic disk unit.
Direct Access: A method of storage where each storage position has a unique address and can be individually accessed in approximately the same period of time without having to search through other storage positions.
Extended BIOS Data Area: A block of memory, typically the 1K at the top of conventional memory, which is used to store additional data for use by the BIOS which does not fit into the 256-byte data area at segment 0040h.
www.datadoctor.biz /miscellaneous-services5.html   (579 words)

  
 Direct memory access controller (EP0328450B1)
The programmable logic array part is coupled to the internal bus and outputs control information required during a next transfer cycle during one transfer cycle which corresponds to a predetermined number of system clock cycles.
Each data transfer between the input/output device and the memory device is controlled by the microprograms of the microsequencer in cooperation with the programmable logic array part.
A direct memory access controller coupled to a system bus (38, 39) of a system including an input/output device (51) and a memory device (52), for controlling a data transfer by direct memory access, said direct memory access controller comprising :
www.delphion.com /details?pn=EP00328450B1   (243 words)

  
 Direct memory access   (Site not responding. Last check: 2007-10-22)
Direct memory access (DMA) allows certain hardware subsystems within a computer to access system memory for reading writing independently of the main CPU.
DMA is an essential feature of all computers as it allows devices of different to communicate without subjecting the CPU to massive interrupt load.
"Scatter-gather" DMA allows the transfer of data multiple memory areas in a single DMA It is equivalent to the chaining together multiple simple DMA requests.
www.freeglossary.com /Direct_memory_access   (338 words)

  
 What is DMA? - A Word Definition From the Webopedia Computer Dictionary
Short for direct memory access, a technique for transferring data from main memory to a device without passing it through the CPU.
Computers that have DMA channels can transfer data to and from devices much more quickly than computers without a DMA channel can.
When you install the board, you must specify which DMA channel is to be used, which sometimes involves setting a jumper or DIP switch.
www.webopedia.com /TERM/D/DMA.html   (152 words)

  
 CSE240 - Direct video memory access   (Site not responding. Last check: 2007-10-22)
On standard VGA graphics cards, the video memory for the screen in standard 80x25 text mode is located at segment B800h.
In addition, it is important to note that video memory is set up in charcter-attribute pairs, with characters at the even offsets and attributes at the odd offsets.
If the command was typed on the bottom line of the screen, the screen will scroll by 1 or 2 lines when the program returns to DOS, scrolling the output off the screen faster than it can be seen.
www.engr.uconn.edu /~jeffm/Help/CSE240/dvm.html   (233 words)

  
 RedTeam: Updated Advisory: FireWire/IEEE 1394 direct memory access - CAN-2004-1038
Systems that counted on physical access limitation such as blocking access to reset and power switches and other measures to limit compromise though such procedures as rebooting, need to re-examine their security.
As usual, physical access to a computer usually implies the ability for compromise - however, with this new technique, merely plugging in a malicious FireWire client device with special software could be enough to compromise a target.
While OHCI supplies certain methods to allow the filtering of such direct memory access requests, most operating systems do not use this filters or do not provide a way for the user to set such filters.
blogs.23.nu /RedTeam/stories/5252   (834 words)

  
 Dr. Dobb's | Direct Memory Access From PC Fortrans | July 22, 2001   (Site not responding. Last check: 2007-10-22)
A pair of c$pragma directives is being used in order to specify that the first argument to PEEKBO and CRTPUT must be passed by value, and that the remaining ones should go by reference.
The conditional compilation directives in Listing Four can be seen to be automatically selecting the appropriate address format for real or protected mode, so that the same source code can be used with either of the Watcom compilers.
The general structure of a program that does direct memory operations is shown in Figure 2.
www.ddj.com /184408998?pgno=2   (4404 words)

  
 IRQ, DMA and Addresses -Interrupt Requests, Direct Memory Access
However, channel 4 is lost since it is used by the Direct memory access controller.
This is often referred to as "fly-by" and provides a limitation in the sense that DMA can only move data between devices (I/O ports) and memory.
It is a memory location used by the device for interfacing with the computer.
www.hildrum.com /IRQ1.htm   (778 words)

  
 Remote Direct Memory Access - Wikipedia, the free encyclopedia
Remote Direct Memory Access (RDMA) allows data to move directly from the memory of one computer into that of another without involving either one's operating system.
RDMA supports zero-copy networking by enabling the network adapter to transfer data directly to or from application memory, eliminating the need to copy data between application memory and the data buffers in the operating system.
The common way to notify it is to change a memory byte when the data has been delivered, but it requires the target to poll on this byte.
en.wikipedia.org /wiki/Remote_Direct_Memory_Access   (474 words)

  
 Direct Memory Access
The first class contains two basic functions: one for initializing the DMA controller chip, one for allocating a suitably aligned buffer.
A set of programs demonstrating the various functions supplied in the library is available for downloading.
Note that while these functions work well under 16-bit DOS, VDS services which automatically transfer data between the user's buffer and the VDS services' buffer always fail to successfully transfer the data under 32-bit DOS.
members.shaw.ca /lwhaynes/c/dma.html   (107 words)

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