IMPLEMENTATION

The tme shell script runs the pcieportmux_gen.tcl script.  It looks at the
ports file that describes the ports on the user circuit, and constructs
pcie_portmux.v from the pcie_portmux.v.template file.  pcie_portmux.v, along
with pcie_reconfig.v and the files in the qsys directory, is copied to the
user's circuit source directory and compiled into the circuit by Quartus.

pcie_portmux connects to the user circuit ports, and communicates over the
PCIe bus using the components defined in the qsys/qsys.qsys file.  That
file has been compiled by the Quartus qsys tool, creating the Verilog
source in qsys/qsys.  It describes a system that includes a PCIe IP core,
along with two sgdma (scatter-gather direct memory access) cores that will
copy data over the PCIe bus using DMA.
