Use Updruino FPGA boarad (iCE40-UP5K-SG48) as bridge between ZX Spectrum and Raspberry Pi
This project uses iCE40-UP5K-SG48 in "CRAM" mode.
By default Updruino ships in "flash mode".
You must re-solder two 0Ohm resistors from Horizontal "Flash" positions to vertical "CRAM" positions.