  The robot operating system is the de-facto standard for designing and
implementing robotics applications. Several previous works deal with the
integration of heterogeneous accelerators into ROS-based applications. One of
these approaches is ReconROS, which enables nodes to be completely mapped to
hardware. The follow-up work fpgaDDS extends ReconROS by an intra-FPGA data
distribution service to process topic-based communication between nodes
entirely in hardware. However, the application of this approach is strictly
limited to communication between nodes implemented in hardware only. This paper
introduces gateways to close the gap between topic communication in hardware
and software. Gateways aim to reduce data transfers between hardware and
software by synchronizing a hardware-and software-mapped topic. As a result,
data must be transferred only once compared to a separate data transmission for
each subscribing hardware node in the baseline. Our measurements show
significant speedups in multi-subscriber scenarios with large message sizes.
From the conclusions of these measurements, we present a methodology for the
communication mapping of ROS 2 computation graphs. In the evaluation, an
autonomous driving real-world example benefits from the gateway and achieves a
speedup of 1.4.
