AN 829: PCI Express* Avalon® -MM DMA Reference Design

ID 683554
Date 6/11/2018

1.1.2. Avalon® -MM DMA Bridge Module Descriptions

The Avalon-MM interface with DMA includes the following modules:

Figure 2.  PCIe* Avalon® -MM DMA Reference Design Block DiagramThis bock diagram shows both the on-chip memory and external memory options.

Read Data Mover

The Read Data Mover sends memory read Transaction Layer Packet (TLPs) upstream. After the Read Data Mover receives the Completion, the Read Data Mover writes the received data to the on-chip or external memory.

Write Data Mover

The Write Data Mover reads data from the on-chip or external memory and sends the data upstream using memory write TLPs on the PCIe* link.

DMA Descriptor Controller

The Descriptor Controller module manages the DMA read and write operations.

Host software programs internal registers in the Descriptor Controller with the location and size of the descriptor table residing in the host system memory through the Avalon® -MM RX master port. Based on this information, the Descriptor Controller directs the Read Data Mover to copy the entire table to local FIFOs for execution. The Descriptor Controller sends completion status upstream via the Avalon® TX slave (TXS) port.

You can also use your own external descriptor controller to manage the Read and Write Data Movers. However, you cannot change the interface between your own external controller and the Read and Write Data Movers embedded in the reference design.

TX Slave

The TX Slave module propagates Avalon® -MM reads and writes upstream. External Avalon® -MM masters, including the DMA control master, can access system memory using the TX Slave. The DMA Controller uses this path to update the DMA status upstream, using Message Signaled Interrupt (MSI) TLPs.

RX Master (Internal Port for BAR0 Control)

The RX Master module propagates single dword read and write TLPs from the Root Port to the Avalon® -MM domain via a 32-bit Avalon® -MM master port. Software instructs the RX Master to send control, status, and descriptor information to Avalon® -MM slaves, including the DMA control slave. The RX Master port is an internal port that not visible in Platform Designer.

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