Xilinx KCU105 User Manual page 61

Performing Transfers using the XDMA Driver with Linux
Use these steps to prepare the application driver to use the XDMA driver to transfer data
between the host and EP in a Linux environment. Passing of an OUT direction parameter
indicates to the XDMA driver that the SGL is a source-side SGL; passing of an IN parameter
indicates to the XDMA driver that the SGL is a destination-side SGL.
S2C I/O
In these steps channel 0 is used and data from the host I/O buffer resident at a virtual
address of 0x12340000 has to be transferred to a fixed AXI address of 0x12340000) in the
EP.
1. Create a source SGL software descriptor using XDMA API xlnx_get_dma_channel ().
Specify the direction as OUT. Call this descriptor s2c_chann0_out_desc. This is the
descriptor for source SGL.
2. Allocate queues for the SGL using XDMA API xlnx_alloc_queues ().
3. Activate the DMA channel using XDMA API xlnx_activate_dma_channel ().
4. Invoke XDMA API xlnx_data_frag_io () passing parameters s2c_chann0_out_desc,
0x12340000, and address type as VIRT_ADDR. A pointer to a callback function also can
be passed (optional).
This causes the data to be drained from the host I/O buffer pointed to by 0x12340000
to the EP memory pointed to by a BD element populated by hardware logic. The host
side software stays agnostic of this location. Optional callbacks are invoked for SGL
descriptors so that application drivers can do necessary post-data transfer clean up.
C2S I/O
In these steps channel 1 is used and data from the EP has to be transferred to a host I/O
buffer at a physical address of 0x880000.
1. Create a destination SGL software descriptor using XDMA API xlnx_get_dma_channel ().
Specify the direction as IN. For this example, the descriptor is called
c2s_chann1_in_desc. This is the descriptor for destination SGL.
2. Allocate Qs for the SGL using XDMA API xlnx_alloc_queues ().
3. Activate the DMA channel using XDMA API xlnx_activate_dma_channel ().
4. Invoke XDMA API xlnx_data_frag_io () passing parameters c2s_chann1_in_desc,
0x880000, and address type as PHYS_ADDR. A pointer to a callback function also can
be optionally passed.
This causes the data to be drained from the EP I/O buffer to the host I/O buffer physical
address location 0x880000. The host software is agnostic of the EP memory location
PCIe Streaming Data Plane TRD
UG920 (v2017.1) June 01, 2017
Chapter 5: Targeted Reference Design Details and Modifications
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