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The Zynq SoC from Xilinx Inc. has a built in hard ARM processor, a dual core Cortex-A9.
This is a port that I am currently considering to use in a serious project, so there were probably more tests and experiments done on it than on any of the others.
The nice thing about using Xilinx hardware is that they come with a full set of drivers for all the hardware on the board or whatever IP block Xilinx supplies for the FPGA. Thus it is easy to create a functional system with relatively little effort.
What I like is that most of the Xilinx solutions work straight out of the box.
You can literally drop in the RTOS of your choice, hook up drivers and you are good to go. This seems to be true for both ARM and MicroBlaze based solutions.
Considering how much work it is to get all the hardware on any board to work corectly, and that I don't necessarily want to deal with it, kudos to Xilinx for making it easy to interface to their stuff.
The port was developed on a ZedBoard demo board.