
8201, 8202, 8203, 8204 Acceleration Processor Data Sheet, DS-0157-05
Page 101
Exar Confidential
3.3 Command Operation Sequence
The 820x has a high performance DMA engine that supports two command pointer rings
using a round-robin arbitration scheme.
Figure 3-25 shows how the 820x and the host
software work together to process a command. The flow is described in the figure below.
1. Host configures the 820x control registers (Refer to
Chapter 6 for details).
2. Host sets up Command Pointer Ring 0 and Command Pointer Ring 1 and writes the
command structures into host memory.
3. Host writes the source data into the source buffers.
4. Host writes the index number of the commands into the Command Pointer Ring
using the 820x Command Pointer Ring Write Pointer (Wcp) register and updates its
own Command Pointer Ring Write Pointer (Wch). The 820x maintains a Command
Pointer Ring Read Pointer (Rcp) register which may be read by the host at any
time. It is the responsibility of the host not to overflow the Command Pointer Ring
by ensuring that the write pointer never advances to meet the read pointer. If
several commands are ready for submission at the same time, the host may build
the command structures for all these commands and then issue a single write to
the write pointer register to improve efficiency.
Figure 3-25. Command Process Flow Example