Prolific tutorial author Dave Vandenbout, Ph.D., produced this nice tutorial book around Xilinx’ Xula board (an open source design based on a Spartan-3 FPGA).
In this book he covers, among other topics:
- How to start an FPGA project.
- How to target a design to a particular type of FPGA.
- How to describe a logic circuit using VHDL and/or schematics.
- How to detect and fix VHDL syntactical errors.
- How to synthesize a netlist from a circuit description.
- How to simulate a circuit.
- How to generate and download a bitstream for an FPGA.
- How to test the programmed FPGA.
- How to detect and fix errors.
And regarding design units:
- How to build hierarchical designs.
- How to build mixed-mode designs using VHDL, Verilog and schematics.
- How to use Digital Clock Managers.
- How to use block RAMs.
The book is available here.
Since I have noticed that this link has frequent availability problems (at least at my location), I have also hosted the book here.
The source files for the tutorials are hosted at Github