Dma controller in computer architecture

Definition: DMA or Direct Memory Access Controller is an external device that controls the transfer of data between I/O device and memory without the involvement of the processor. It holds the ability to directly access the main memory for read or write operation. DMA controller was designed by Intel, to have the fastest data transfer rate with less processor utilization. We know in order to execute an operation, the So, to enhance the performance of the processor, an external device is used that can manage data transfer operation between peripherals and memory with least CPU utilization. Basically, it is nothing but hardware controlled data transfer, where the address and control signals required for transferring the data is generated by an external device. This method of data transfer is known as direct memory access and the external device used for this purpose is known as DMA controller. Need: We know that generally whenever there exists a need for transfer of data between peripherals and main memory, then first the data is given to the processor by the input device and then the processor further transfers the data to the memory. And at the time of data transfer operation, the processor cannot be able to execute any other operation. Hence when the system has a DMA controller then it frees the CPU from data transfer operation and at that particular time being the CPU can execute other operations. Till now we have discussed the need of DMA controller let us move further ...

Previous Tutorial Tutorial 21 Next Tutorial STM32 DMA Tutorial – Using Direct Memory Access (DMA) In STM32 STM32 Course Home Page 🏠 In this tutorial, we’ll discuss the direct memory access unit (DMA) in STM32 microcontrollers. We’ll begin with an introduction for what is a DMA unit, when, and why to use it. Afterward, we’ll start discussing the STM32 DMA hardware, its features, and how to configure it in your projects. And some example applications that we’ll be building throughout this course. [toc] What Is Direct Memory Access (DMA)? A Direct Memory Access (DMA) unit is a digital logic element in computer architecture that can be used in conjunction with the main microprocessor on the same chip in order to offload the memory transfer operations. This significantly reduces the CPU load. As the DMA controller can perform memory to memory data transfers as well as peripheral to memory data transfers or vice versa. The existence of DMA with a CPU can accelerate its throughput by orders of magnitude. In no-DMA computer architecture, you’d find it looking something like this shown in the diagram below. As you can see, the CPU (main processor) has to do all the work of fetching instructions (code) from flash, executing the decoded instructions, and move data to and from peripherals and memory. Imagine having a UART1 data receiver that gets a stream of data that the CPU has to immediately transfer to a local buffer in memory so as not to lose any data packet. This translates int...

\( \newcommand\) • • • • • • • • • • Channel I/O Channel I/O is a high-performance I/Oarchitecture that is implemented in various forms on a number of computer architectures, especially on mainframe computers. In the past, channels were generally implemented with custom devices, variously named channel, I/O processor, I/O controller, I/O synchronizer, or DMA controller. Description Many I/O tasks can be complex and require logic to be applied to the data to convert formats and other similar duties. In these situations, the simplest solution is to ask the CPU to handle the logic, but because I/O devices are relatively slow, a CPU could waste time (in computer perspective) waiting for the data from the device. This situation is called 'I/O bound'. Channel architecture avoids this problem by using a logically independent, low-cost facility. Channel processors are simple, but self-contained, with minimal logic and sufficient scratch-pad memory (working storage) to handle I/O tasks. They are typically not powerful or flexible enough to be used as a computer on their own and can be construed as a form of coprocessor. On some systems the channels use memory or registers addressable by the central processor as their scratchpad memory, while on other systems it is present in the channel hardware. Typically there are standard interfaces between channels and external peripheral devices, and multiple channels can operate concurrently. A CPU typically designates a block of storage or s...

DMA Controller Diagram in Computer Architecture DMA Controller is a type of control unit that works as an interface for the data bus and the I/O Devices. As mentioned, DMA Controller has the work of transferring the data without the intervention of the processors, processors can control the data transfer. DMA Controller also contains an address unit, which generates the address and selects an I/O device for the transfer of data. Here we are showing the block diagram of the DMA Controller. • Single-Ended DMA • Dual-Ended DMA • Arbitrated-Ended DMA • Interleaved DMA Single-Ended DMA: Single-Ended DMA Controllers operate by reading and writing from a single memory address. They are the simplest DMA. Dual-Ended DMA: Dual-Ended DMA controllers can read and write from two memory addresses. Dual-ended DMA is more advanced than single-ended DMA. Arbitrated-Ended DMA: Arbitrated-Ended DMA works by reading and writing to several memory addresses. It is more advanced than Dual-Ended DMA. Interleaved DMA: Interleaved DMA are those DMA that read from one memory address and write from another memory address. Working of DMA Controller The • Address register –It contains the address to specify the desired location in memory. • Word count register –It contains the number of words to be transferred. • Control register –It specifies the transfer mode. Note: All registers in the DMA appear to the The figure below shows the block diagram of the DMA controller. The unit communicates with the CP...

From Section 5.1.4 Direct Memory Access in Modern Operating Systems by Andrew S. Tanenbaum, Herbert Bos, 2014, To simplify the explanation, we assume that the CPU accesses all devices and memory via a single system bus that connects the CPU, the memory, and the I/O devices, as shown in Fig. 5-4. • To explain how DMA works, let us first look at how disk reads occur when DMA is not used. • First the disk controller reads the block (one or more sectors) from the drive serially, bit by bit, until the entire block is in the controller’s internal buffer. • Next, it computes the checksum to verify that no read errors have occurred. Then the controller causes an interrupt. When the operating system starts running, it can read the disk block from the controller’s buffer a byte or a word at a time by executing a loop, with each iteration reading one byte or word from a controller device register and storing it in main memory. Q: in the second step, • isn't the data transferred " from the controller's buffer" to the main memory? Why does it say both " from the controller’s buffer" and " from a controller device register"? • in the second step, can the controller transfer data from its buffer to the main memory, without interrupting to the cpu, and without involving OS again? • When DMA is used, the procedure is different. • First the CPU programs the DMA controller by setting its registers so it knows what to transfer where (step 1 in Fig. 5-4). It also issues a command to the disk c...