The function of the initiator block is to generate memory write or memory read TLPs depending on whether an upstream or downstream transfer is selected. The Bus Master DMA design only supports generating one type of a data flow at a single time. The Bus Master enable bit (Bit 2 of PCI Command Register) must be set to initiate TLP traffic upstream. No transactions are allowed to cross the 4K boundary.
The initiator logic generates memory write TLPs when transferring data from the endpoint to system memory. The Write DMA control and status registers specify the address, size, payload content, and number of TLPs to be sent.
All registers are defined in Appendix A: Design Descriptor Registers of Bus Master Performance Demonstration Reference Design for the Xilinx Endpoint PCI Express Solutions (XAPP1052).
The following table shows BMD design file structure for 64/128/256-bit configuration.
| File | Description |
|---|---|
| BMD_AXIST.v | Top-level design wrapper |
| BMD_AXIST_EP.v | Top-level module |
| BMD_AXIST_EP_MEM_ACCESS.v | Memory access module |
| BMD_AXIST_EP_MEM.v | Memory module |
| BMD_AXIST_TX_ENGINE.v | BMD Transmit engine |
| BMD_AXIST_RX_ENGINE.v | BMD Receive engine |
| BMD_AXIST_INTR_CTRL.v | Interrupt controller |
| BMD_AXIST_TO_CTRL.v | Turn-off controller module |
The following table shows BMD design file structure for 512-bit configuration.
| File | Description |
|---|---|
| BMD_AXIST_512.v | Top-level design wrapper |
| BMD_AXIST_EP_512.v | Top-level module |
| BMD_AXIST_EP_MEM_ACCESS.v | Memory access module |
| BMD_AXIST_EP_MEM.v | Memory module |
| BMD_AXIST_RC_512.v | BMD Requester Completion module |
| BMD_AXIST_CQ_512.v | BMD Completer Request module |
| BMD_AXIST_RQ_512.v | BMD Requester Request module |
| BMD_AXIST_RQ_WRITE_512.v | BMD Requester Request write module |
| BMD_AXIST_RQ_READ_512.v | BMD Requester Request read module |
| BMD_AXIST_RQ_MUX_512.v | BMD Requester Write/Read MUX module |
| BMD_AXIST_CC_512.v | BMD Completer Completion module |
| BMD_AXIST_INTR_CTRL.v | Interrupt controller |
| BMD_AXIST_TO_CTRL.v | Turn-off controller module |