Meaning
Sequential memory transfers occur between peripherals and system memory without direct intervention from the central processing unit to maximize data throughput. A direct memory access sweep allows a controller to verify the contents of a large buffer or clear a specific range of addresses in one continuous operation. The process ends once the final byte in the designated memory block moves to its destination, signaling the end of the transfer to the host.
Transfer Latency
Bus arbitration determines how quickly the controller gains control of the signal lines to start the move. While a direct memory access sweep is active, the main processor might experience delays if it tries to access the same memory bank.
Controller Overhead
Setup requirements involve loading the start address, the word count and the trigger condition into the hardware registers. The direct memory access sweep then proceeds independently, freeing the software to handle other tasks. Completion is signaled by an interrupt that tells the operating system the buffer is ready.
Data Alignment
Hardware constraints often require the starting point and length of the transfer to match specific byte boundaries. If a direct memory access sweep targets an unaligned address, the transfer speed might drop or the system could generate a bus error. Properly aligned buffers maximize the throughput of the interconnect and ensure the controller functions at its maximum rated speed.
