Black Mesa Labs created this board that adds a Lattice FPGA to a Raspberry Pi:

IceZero FPGA Board for RaspPi

BML has been very much enchanted with the Lattice FPGA boards for Raspberry Pi, IcoBoard , BlackIce and IceHat. The IceZero board is a BML creation that attempts to combine the best features of all 3 boards into a single design.

IceZero features common with other designs

• Fully Open-Source Hardware and Software Design.
• Lattice ICE40HX4K FPGA that supports Clifford Wolf’s Project IceStorm tool chain.
• Interfaces to Raspberry Pi 2×20 GPIO Header for both power and bus interfaces.
• PROM programmable directly from Rasp Pi, no JTAG programmer required.
• External SRAM, supporting soft CPU core designs ( code execution ).
• Extra large SPI PROM, supporting soft CPU core designs ( code storage ).
• Industry standard PMOD expansion headers

IceZero features that are BML specific

• Mesa Bus Protocol 32 MHz SPI link between CPU and FPGA.
• 2-Layer PCB design. Orderable via OSH-Park or Gerbers for Downloading.
• FTDI 1×6 USB Serial Cable header for use with PC instead of Pi ( or as a soft CPU debug Trace Port ).
• Single Pi UART plumbed to FPGA for muxing to multiple external serial devices.

BlackMesaLabs has shared the board on OSH Park:

bml_ice_zero_19_02.zip

BML IceZero Lattice ICE40 FPGA for RaspPi