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55-411: I/O Acceleration Technology ( I/OAT ) is a DMA engine (an embedded DMA controller ) by Intel bundled with high-end server motherboards , that offloads memory copies from the main processor by performing direct memory accesses (DMA). It is typically used for accelerating network traffic, but supports any kind of copy. Using I/OAT for network acceleration is supported by Microsoft Windows since

110-400: A computer system bus which acts as the host system to other network and storage devices. The terms are primarily used to refer to devices for connecting SCSI , SAS , NVMe , Fibre Channel and SATA devices. Devices for connecting to FireWire , USB and other devices may also be called host controllers or host adapters. Host adapters can be integrated in the motherboard or be on

165-452: A processing circuitry 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. DMA can offload expensive memory operations, such as large copies or scatter-gather operations, from the CPU to

220-455: A 16-bit address register and a 16-bit count register associated with it. 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 instructs the DMA hardware to begin the transfer. When the transfer is complete, the device interrupts the CPU. Scatter-gather or vectored I/O DMA allows

275-421: A DMA command can transfer either a single block area of size up to 16 KB, or a list of 2 to 2048 such blocks. The DMA command is issued by specifying a pair of a local address and a remote address: for example when a SPE program issues a put DMA command, it specifies an address of its own local memory as the source and a virtual memory address (pointing to either the main memory or the local memory of another SPE) as

330-590: A DMA engine called I/O Acceleration Technology (I/OAT), which can offload memory copying from the main CPU, freeing it to do other work. In 2006, Intel's Linux kernel developer Andrew Grover performed benchmarks using I/OAT to offload network traffic copies and found no more than 10% improvement in CPU utilization with receiving workloads. Further performance-oriented enhancements to the DMA mechanism have been introduced in Intel Xeon ;E5 processors with their Data Direct I/O ( DDIO ) feature, allowing

385-495: A PCI component requests bus ownership from the PCI bus controller (usually PCI host bridge, and PCI to PCI bridge ), which will arbitrate if several devices request bus ownership simultaneously, since there can only be one bus master at one time. When the component is granted ownership, it will issue normal read and write commands on the PCI bus, which will be claimed by the PCI bus controller. As an example, on an Intel Core -based PC,

440-435: A block of data, yet it is also the most efficient mode in terms of overall system performance. In transparent mode, the DMA controller transfers data only when the CPU is performing operations that do not use the system buses. The primary advantage of transparent mode is that the CPU never stops executing its programs and the DMA transfer is free in terms of time, while the disadvantage is that the hardware needs to determine when

495-495: A built-in floppy disk controller, an IrDA infrared controller when FIR (fast infrared) mode is selected, and an IEEE 1284 parallel port controller when ECP mode is selected. In cases where an original 8237s or direct compatibles were still used, transfer to or from these devices may still be limited to the first 16 MB of main RAM regardless of the system's actual address space or amount of installed memory. Each DMA channel has

550-428: A cascade to the first 8237). The page register was also rewired to address the full 16 MB memory address space of the 80286 CPU. This second controller was also integrated in a way capable of performing 16-bit transfers when an I/O device is used as the data source and/or destination (as it actually only processes data itself for memory-to-memory transfers, otherwise simply controlling the data flow between other parts of

605-480: A dedicated DMA engine. An implementation example is the I/O Acceleration Technology . DMA is of interest in network-on-chip and in-memory computing architectures. Standard DMA, also called third-party DMA, uses a DMA controller. A DMA controller can generate memory addresses and initiate memory read or write cycles. It contains several hardware registers that can be written and read by

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660-649: A feature that maintains compatibility with the priority scheme of the 8-bit or "narrow" bus). The host adapter usually assumes the role of SCSI initiator , in that it issues commands to other SCSI devices. A computer can contain more than one host adapter, which can greatly increase the number of SCSI devices available. Major SCSI adapter manufacturers are HP , ATTO Technology , Promise Technology, Adaptec , and LSI Corporation . LSI, Adaptec, and ATTO offer PCIe SCSI adapters which fit in Apple Mac, on Intel PCs, and low-profile motherboards which lack SCSI support due to

715-467: A method in hardware, called bus snooping , whereby external writes are signaled to the cache controller which then performs a cache invalidation for DMA writes or cache flush for DMA reads. Non-coherent systems leave this to software, where the OS must then ensure that the cache lines are flushed before an outgoing DMA transfer is started and invalidated before a memory range affected by an incoming DMA transfer

770-500: A separate expansion card . The term network interface controller (NIC) is more often used for devices connecting to computer networks, while the term converged network adapter can be applied when protocols such as iSCSI or Fibre Channel over Ethernet allow storage and network functionality over the same physical connection. A SCSI host adapter connects a host system and a peripheral SCSI device or storage system. These adapters manage service and task communication between

825-676: A unique World Wide Name (WWN), which is similar to an Ethernet MAC address in that it uses an OUI assigned by the IEEE . However, WWNs are longer (8 bytes). There are two types of WWNs on a HBA; a node WWN (WWNN), which is shared by all ports on a host bus adapter, and a port WWN (WWPN), which is unique to each port. There are HBA models of different speeds: 1 Gbit/s, 2 Gbit/s, 4 Gbit/s, 8 Gbit/s, 10 Gbit/s, 16 Gbit/s, 20 Gbit/s and 32 Gbit/s. The major Fibre Channel HBA manufacturers are QLogic and Broadcom . As of mid-2009, these vendors shared approximately 90% of

880-563: Is a similar technology from the aspect of connection options. HBAs can be created using a single connector to connect both SAS and SATA devices. Major SAS/SATA adapter manufacturers are Promise Technologies, Adaptec , HP , QLogic , Areca, LSI and ATTO Technology . External Serial ATA (eSATA) disk enclosures and drives are available in the consumer computing market, but not all SATA-compatible motherboards and disk controllers include eSATA ports. As such, adapters to connect eSATA devices to ports on an internal SATA bus are available. In

935-461: Is accessed. The OS must make sure that the memory range is not accessed by any running threads in the meantime. The latter approach introduces some overhead to the DMA operation, as most hardware requires a loop to invalidate each cache line individually. Hybrids also exist, where the secondary L2 cache is coherent while the L1 cache (typically on-CPU) is managed by software. In the original IBM PC (and

990-473: Is similar to programmed I/O through which the software (running on embedded CPU, e.g. ARM ) can write/read I/O registers or (less commonly) local memory blocks inside the device. A master interface can be used by the device to perform DMA transactions to/from system memory without heavily loading the CPU. Therefore, high bandwidth devices such as network controllers that need to transfer huge amounts of data to/from system memory will have two interface adapters to

1045-520: Is useful at any time that the CPU cannot keep up with the rate of data transfer, or when the CPU needs to perform 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 some multi-core processors . Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without DMA channels. Similarly,

1100-433: The 16-bit system, making its own data bus width relatively immaterial), doubling data throughput when the upper three channels are used. For compatibility, the lower four DMA channels were still limited to 8-bit transfers only, and whilst memory-to-memory transfers were now technically possible due to the freeing up of channel 0 from having to handle DRAM refresh, from a practical standpoint they were of limited value because of

1155-527: The AHB: a master and a slave interface. This is because on-chip buses like AHB do not support tri-stating the bus or alternating the direction of any line on the bus. Like PCI, no central DMA controller is required since the DMA is bus-mastering, but an arbiter is required in case of multiple masters present on the system. Internally, a multichannel DMA engine is usually present in the device to perform multiple concurrent scatter-gather operations as programmed by

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1210-508: The AT due to ISA bus overheads and other interference such as memory refresh interruptions ) and unavailability of any speed grades that would allow installation of direct replacements operating at speeds higher than the original PC's standard 4.77 MHz clock, these devices have been effectively obsolete since the late 1980s. Particularly, the advent of the 80386 processor in 1985 and its capacity for 32-bit transfers (although great improvements in

1265-462: The CPU and DMA controller. Each DMA channel has one Request and one Acknowledge line. A device that uses DMA must be configured to use both lines of the assigned DMA channel. 16-bit ISA permitted bus mastering. Standard ISA DMA assignments: A PCI architecture has no central DMA controller, unlike ISA. Instead, A PCI device can request control of the bus ("become the bus master ") and request to read from and write to system memory. More precisely,

1320-425: The CPU is not using the system buses, which can be complex. This is also called " Hidden DMA data transfer mode ". [REDACTED] DMA can lead to cache coherency problems. Imagine a CPU equipped with a cache and an external memory that can be accessed directly by devices using DMA. When the CPU accesses location X in the memory, the current value will be stored in the cache. Subsequent operations on X will update

1375-401: 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 first initiates the transfer, then it does other operations while the transfer is in progress, and it finally receives an interrupt from the DMA controller (DMAC) when the operation is done. This feature

1430-537: The CPU. These include a memory address register, a byte count register, and one or more control registers. Depending on what features the DMA controller provides, these control registers might specify some combination of the source, the destination, the direction of the transfer (reading from the I/O device or writing to the I/O device), the size of the transfer unit, and/or the number of bytes to transfer in one burst. To carry out an input, output or memory-to-memory operation,

1485-504: The DMA "windows" to reside within CPU caches instead of system RAM. As a result, CPU caches are used as the primary source and destination for I/O, allowing network interface controllers (NICs) to DMA directly to the Last level cache (L3 cache) of local CPUs and avoid costly fetching of the I/O data from system RAM. As a result, DDIO reduces the overall I/O processing latency, allows processing of

1540-445: The I/O to be performed entirely in-cache, prevents the available RAM bandwidth/latency from becoming a performance bottleneck, and may lower the power consumption by allowing RAM to remain longer in low-powered state. In systems-on-a-chip and embedded systems , typical system bus infrastructure is a complex on-chip bus such as AMBA High-performance Bus . AMBA defines two kinds of AHB components: master and slave. A slave interface

1595-637: The PC, limited by the general PIO speed of the CPU, were very slow. With the IBM PC/AT , the enhanced AT bus (more familiarly retronymed as the Industry Standard Architecture (ISA)) added a second 8237 DMA controller to provide three additional, and as highlighted by resource clashes with the XT's additional expandability over the original PC, much-needed channels (5–7; channel 4 is used as

1650-443: The PCI bus and the device itself, enables 64-bit DMA addressing. Otherwise, the operating system would need to work around the problem by either using costly double buffers (DOS/Windows nomenclature) also known as bounce buffers ( FreeBSD /Linux), or it could use an IOMMU to provide address translation services if one is present. As an example of DMA engine incorporated in a general-purpose CPU, some Intel Xeon chipsets include

1705-482: The cached copy of X, but not the external memory version of X, assuming a write-back cache . If the cache is not flushed to the memory before the next time a device tries to access X, the device will receive a stale value of X. Similarly, if the cached copy of X is not invalidated when a device writes a new value to the memory, then the CPU will operate on a stale value of X. This issue can be addressed in one of two ways in system design: Cache-coherent systems implement

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1760-431: The component that allows a computer to talk to a peripheral bus is host adapter . A proper disk controller only allows a disk to talk to the same bus. SAS or serial-attached SCSI is the current connectivity to replace the previous generation parallel-attached SCSI (PAS) devices. Ultra320 was the highest level of parallel SCSI available, but SAS has since replaced it as the highest-performing SCSI technology. SATA

1815-422: The controller's consequent low throughput compared to what the CPU could now achieve (i.e., a 16-bit, more optimised 80286 running at a minimum of 6 MHz, vs an 8-bit controller locked at 4.77 MHz). In both cases, the 64 kB segment boundary issue remained, with individual transfers unable to cross segments (instead "wrapping around" to the start of the same segment) even in 16-bit mode, although this

1870-529: The efficiency of address calculation and block memory moves in Intel CPUs after the 80186 meant that PIO transfers even by the 16-bit-bus 286 and 386SX could still easily outstrip the 8237), as well as the development of further evolutions to ( EISA ) or replacements for ( MCA , VLB and PCI ) the "ISA" bus with their own much higher-performance DMA subsystems (up to a maximum of 33 MB/s for EISA, 40 MB/s MCA, typically 133 MB/s VLB/PCI) made

1925-421: The follow-up PC/XT ), there was only one Intel 8237 DMA controller capable of providing four DMA channels (numbered 0–3). These DMA channels performed 8-bit transfers (as the 8237 was an 8-bit device, ideally matched to the PC's i8088 CPU/bus architecture), could only address the first ( i8086 /8088-standard) megabyte of RAM, and were limited to addressing single 64  kB segments within that space (although

1980-422: The full block of data is transferred. Some examples of buses using third-party DMA are PATA , USB (before USB4 ), and SATA ; however, their host controllers use bus mastering . In a bus mastering system, also known as a first-party DMA system, the CPU and peripherals can each be granted control of the memory bus. Where a peripheral can become a bus master, it can directly write to system memory without

2035-523: The host and target. Typically a device driver , linked to the operating system , controls the host adapter itself. In a typical parallel SCSI subsystem, each device has assigned to it a unique numerical ID. As a rule, the host adapter appears as SCSI ID 7, which gives it the highest priority on the SCSI bus (priority descends as the SCSI ID descends; on a 16-bit or "wide" bus, ID 8 has the lowest priority,

2090-458: The host processor initializes the DMA controller with a count of the number of words to transfer, and the memory address to use. The CPU then commands the peripheral device to initiate a data transfer. The DMA controller then provides addresses and read/write control lines to the system memory. Each time a byte of data is ready to be transferred between the peripheral device and memory, the DMA controller increments its internal address register until

2145-551: The inclusion of SAS and/or SATA connectivity. The term host bus adapter (HBA) may be used to refer to a Fibre Channel interface card. In this case, it allows devices in a Fibre Channel storage area network to communicate data between each other – it may connect a server to a switch or storage device, connect multiple storage systems, or connect multiple servers. Fibre Channel HBAs are available for open systems , computer architectures, and buses, including PCI and SBus (obsolete today). Each Fibre Channel HBA has

2200-433: The involvement of the CPU, providing memory address and control signals as required. Some measures must be provided to put the processor into a hold condition so that bus contention does not occur. In burst mode , an entire block of data is transferred in one contiguous sequence. Once the DMA controller is granted access to the system bus by the CPU, it transfers all bytes of data in the data block before releasing control of

2255-495: The main memory and local memories of other SPEs. Thus the DMA acts as a primary means of data transfer among cores inside this CPU (in contrast to cache-coherent CMP architectures such as Intel's cancelled general-purpose GPU , Larrabee ). DMA in Cell is fully cache coherent (note however local stores of SPEs operated upon by DMA do not act as globally coherent cache in the standard sense ). In both read ("get") and write ("put"),

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2310-433: The market. Other manufacturers include Agilent , ATTO , and Brocade . HBA is also known to be interpreted as High Bandwidth Adapter in cases of Fibre Channel controllers. The term host channel adapter ( HCA ) is usually used to describe InfiniBand interface cards. ATA host adapters are integrated into motherboards of most modern PCs . They are often improperly called disk controllers . The correct term for

2365-426: The on-chip memory is split into two buffers; the processor may be operating on data in one, while the DMA engine is loading and storing data in the other. This allows the system to avoid memory latency and exploit burst transfers , at the expense of needing a predictable memory access pattern . Host controller In computer hardware a host controller , host adapter or host bus adapter ( HBA ) connects

2420-532: The original DMA controllers seem more of a performance millstone than a booster. They were supported to the extent they are required to support built-in legacy PC hardware on later machines. The pieces of legacy hardware that continued to use ISA DMA after 32-bit expansion buses became common were Sound Blaster cards that needed to maintain full hardware compatibility with the Sound Blaster standard ; and Super I/O devices on motherboards that often integrated

2475-560: The release of Scalable Networking Pack for Windows Server 2003 SP1. However, it is no longer included in Windows from version 8 on-wards. It was used by the Linux kernel starting in 2006 but this feature was subsequently disabled due to an alleged lack of performance benefits while creating a possibility of data corruption. This computing article is a stub . You can help Misplaced Pages by expanding it . DMA engine Without DMA, when

2530-500: The rest of the components (see list of device bandwidths ). A modern x86 CPU may use more than 4 GB of memory, either utilizing the native 64-bit mode of x86-64 CPU, or the Physical Address Extension (PAE), a 36-bit addressing mode. In such a case, a device using DMA with a 32-bit address bus is unable to address memory above the 4 GB line. The new Double Address Cycle (DAC) mechanism, if implemented on both

2585-465: The software. As an example usage of DMA in a multiprocessor-system-on-chip , IBM/Sony/Toshiba's Cell processor incorporates a DMA engine for each of its 9 processing elements including one Power processor element (PPE) and eight synergistic processor elements (SPEs). Since the SPE's load/store instructions can read/write only its own local memory, an SPE entirely depends on DMAs to transfer data to and from

2640-455: The source and destination channels could address different segments). Additionally, the controller could only be used for transfers to, from or between expansion bus I/O devices, as the 8237 could only perform memory-to-memory transfers using channels 0 & 1, of which channel 0 in the PC (& XT) was dedicated to dynamic memory refresh . This prevented it from being used as a general-purpose " Blitter ", and consequently block memory moves in

2695-403: The southbridge will forward the transactions to the memory controller (which is integrated on the CPU die) using DMI , which will in turn convert them to DDR operations and send them out on the memory bus. As a result, there are quite a number of steps involved in a PCI DMA transfer; however, that poses little problem, since the PCI device or PCI bus itself are an order of magnitude slower than

2750-401: The system bus, the DMA controller essentially interleaves instruction and data transfers. The CPU processes an instruction, then the DMA controller transfers one data value, and so on. Data is not transferred as quickly, but CPU is not idled for as long as in burst mode. Cycle stealing mode is useful for controllers that monitor data in real time. Transparent mode takes the most time to transfer

2805-472: The system buses back to the CPU, but renders the CPU inactive for relatively long periods of time. The mode is also called "Block Transfer Mode". The cycle stealing mode is used in systems in which the CPU should not be disabled for the length of time needed for burst transfer modes. In the cycle stealing mode, the DMA controller obtains access to the system bus the same way as in burst mode, using BR ( Bus Request ) and BG ( Bus Grant ) signals, which are

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2860-468: The target, together with a block size. According to an experiment, an effective peak performance of DMA in Cell (3 GHz, under uniform traffic) reaches 200 GB per second. Processors with scratchpad memory and DMA (such as digital signal processors and the Cell processor) may benefit from software overlapping DMA memory operations with processing, via double buffering or multibuffering. For example,

2915-452: The transfer of data to and from multiple memory areas in a single DMA transaction. It is equivalent to the chaining together of multiple simple DMA requests. The motivation is to off-load multiple input/output interrupt and data copy tasks from the CPU. DRQ stands for Data request ; DACK for Data acknowledge . These symbols, seen on hardware schematics of computer systems with DMA functionality, represent electronic signaling lines between

2970-408: The two signals controlling the interface between the CPU and the DMA controller. However, in cycle stealing mode, after one unit of data transfer, the control of the system bus is deasserted to the CPU via BG. It is then continually requested again via BR, transferring one unit of data per request, until the entire block of data has been transferred. By continually obtaining and releasing the control of

3025-497: Was in practice more a problem of programming complexity than performance as the continued need for DRAM refresh (however handled) to monopolise the bus approximately every 15  μs prevented use of large (and fast, but uninterruptible) block transfers. Due to their lagging performance (1.6  MB /s maximum 8-bit transfer capability at 5 MHz, but no more than 0.9 MB/s in the PC/XT and 1.6 MB/s for 16-bit transfers in

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