Visible to Intel only — GUID: iga1401397705387
Ixiasoft
Visible to Intel only — GUID: iga1401397705387
Ixiasoft
30.2. Functional Description
The source and destination may be either an Avalon® -MM agent peripheral (for example, a constant address) or an address range in memory. The DMA controller can be used in conjunction with peripherals with flow control, which allows data transactions of fixed or variable length. The DMA controller can signal an interrupt request (IRQ) when a DMA transaction completes. A transaction is a sequence of one or more Avalon® transfers initiated by the DMA controller core.
The DMA controller has two Avalon® -MM host ports—a host read port and a host write port—and one Avalon® -MM agent port for controlling the DMA as shown in the figure below.
A typical DMA transaction proceeds as follows:
- A CPU prepares the DMA controller for a transaction by writing to the control port.
- The CPU enables the DMA controller. The DMA controller then begins transferring data without additional intervention from the CPU. The DMA’s host read port reads data from the read address, which may be a memory or a peripheral. The host write port writes the data to the destination address, which can also be a memory or peripheral. A shallow FIFO buffers data between the read and write ports.
- The DMA transaction ends when a specified number of bytes are transferred (a fixed-length transaction) or an end-of-packet signal is asserted by either the sender or receiver (a variable-length transaction). At the end of the transaction, the DMA controller generates an interrupt request (IRQ) if it was configured by the CPU to do so.
- During or after the transaction, the CPU can determine if a transaction is in progress, or if the transaction ended (and how) by examining the DMA controller’s status register.