output_gmio object is used to make external memory-mapped
connections to or from the global memory. These connections are made between an
AI Engine graph and the logical global memory
ports of a hardware platform design. The platform can be a base platform from
Xilinx or a custom platform that is exported
from the Vivado tools as a Xilinx device support archive (XSA) package.
AI Engine tools support mapping the
output_gmio port to the tile DMA, one to one. It does not support
output_gmio ports to
one tile DMA channel. There is a limit on the number of
output_gmio ports supported for a
given device. For example, the XCVC1902 device on the VCK190 board has 16 AI Engine to NoC master units (NMU) in total. For each
AI Engine to NMU, it supports two MM2S and
two S2MM channels. So, there can be at most 32 AI Engine GMIO inputs, and 32 AI Engine GMIO outputs. Note that it can be further limited by the
existing hardware platform.
While developing data flow graph applications on top of an existing hardware platform, you need to know what global memory ports are exported by the underlying XSA and their functionality. In particular, any input or output ports exposed on the platform are recorded within the XSA and can be viewed as a logical architecture interface.