Here is the description of Direct Memory Access:
→The data transfer between any fast storage media like a memory unit and a magnetic disk gets limited with the speed of the CPU.
→Thus it will be best to allow the peripherals to directly communicate with the storage using the memory buses by removing the intervention of the CPU. This mode of transfer of data technique is known as Direct Memory Access (DMA).
→During Direct Memory Access, the CPU is idle and has no control over the memory buses. The DMA controller takes over the buses and directly manages data transfer between the memory unit and I/O devices.
Buss Request:
• We use bus requests in the DMA controller to ask the CPU to relinquish the control buses.
Buss Grant:
• CPU activates bus grant to inform the DMA controller that DMA can take control of the control buses. Once the control is taken, it can transfer data in many ways.
Bus Arbitration:
Bus arbitration is a process used in computer systems to manage access to shared resources, such as the system bus, among multiple competing devices or components.
• In a computer system, various components, such as the CPU, memory modules, input/output devices, and other peripherals, need to communicate with each other.
• The system bus serves as the communication pathway through which data and control signals are transferred between these components.
• However, since the system bus can only handle one transaction at a time, there needs to be a mechanism in place to determine which device gets to use the bus at any given moment. This is where bus arbitration comes into play.
DMA Controller:
A DMA (Direct Memory Access) controller is a hardware component in a computer system that allows peripheral devices to transfer data directly to or from the system’s memory without involving the CPU.
- A DMA (Direct Memory Access) controller is a specialized hardware component commonly found in computer systems and embedded devices.
- Its primary function is to facilitate data transfers between peripherals (such as disk drives, network interfaces, and graphics cards) and the main memory (RAM) without involving the CPU for every data transfer operation.
- This offloads the CPU from performing data transfer tasks, freeing it to focus on executing other instructions.
Block Diagram of DMA Controller:
Here’s how a DMA controller typically works:
‣ Initialization:
The DMA controller is initialized by the CPU or the system’s operating system. Initialization involves configuring the DMA controller’s registers, setting up transfer parameters such as source and destination addresses, transfer size, transfer direction, and any necessary control flags.
‣ Data Transfer Request:
When a peripheral device (such as a disk drive or a network interface) needs to transfer data to or from the main memory, it sends a request to the DMA controller. This request includes information about the data transfer, such as the source and destination addresses in memory.
‣ Arbitration:
If multiple peripherals request DMA transfers simultaneously, the DMA controller may use an arbitration mechanism to prioritize and schedule the data transfers based on predefined criteria, such as priority levels or a round-robin scheme.
‣ Data Transfer:
Once the DMA controller receives a transfer request and gains control of the system bus, it initiates the data transfer directly between the peripheral device and the main memory without involving the CPU. The DMA controller uses its internal bus mastering capabilities to perform the transfer efficiently.
‣ Transfer Completion:
After the data transfer is completed, the DMA controller may generate an interrupt or a signal to notify the CPU or the requesting peripheral device about the transfer’s completion. This allows the CPU or the device to continue processing data or perform other tasks as needed.
‣ Error Handling:
The DMA controller may also include error detection and error handling mechanisms to detect and recover from data transfer errors, such as bus conflicts, data corruption, or timeout conditions. Error handling typically involves generating error interrupts or status flags for diagnostic purposes.
DMA Transfer:
DMA (Direct Memory Access) transfer refers to a method of data transfer between peripherals and memory in a computer system without involving the CPU directly in every step of the transfer process.
• DMA allows peripherals like disk drives, network interfaces, and graphics cards to access the system’s memory directly, reducing CPU overhead and improving overall system performance.
