Unconventional HDL Synthesis Experiments: From Spreadsheets to 74 Logic Chips
0:36 Unconventional Synthesis: Pepijn de Vos explores unconventional methods for synthesizing hardware, including using spreadsheets and C code as input for generating logic circuits on FPGAs and using discrete 74 series logic chips.
1:13 Conventional FPGA Synthesis Flow: A traditional FPGA design flow involves using HDL languages (like Verilog or VHDL), synthesis tools (like Yosys), place and route tools (like nextpnr), and finally generating a bitstream for the FPGA.
3:52 ASIC vs. FPGA Synthesis Targets: ASIC synthesis targets a standard cell library specific to the fabrication process, while FPGA synthesis targets the configurable logic blocks (LUTs, multiplexers, flip-flops) within the FPGA.
11:23 Open Source Tools for Flexibility: Open-source tools like Yosys and nextpnr enable experimentation with unconventional synthesis approaches by allowing custom scripts and intermediate representation manipulation.
12:16 Spreadsheet to Hardware: Pepijn explores the concept of synthesizing spreadsheet calculations into hardware, potentially enabling domain experts to directly implement logic without HDL knowledge. He demonstrates a basic implementation using Python to parse spreadsheets and generate Verilog code.
14:36 Challenges of Spreadsheet Synthesis: Handling floating-point numbers in hardware (FPGAs work with binary/fixed-point) and implementing complex spreadsheet functions are identified as challenges.
23:03 74 Series Logic Synthesis: Inspired by others, Pepijn explores synthesizing HDL code into circuits using discrete 74 series logic chips. This involves creating custom Liberty files for Yosys to map logic gates to specific 74 series chips.
26:05 74 Series Chip Selection: 74HC series logic chips are chosen for their availability and cost-effectiveness, with the option of using faster 74AC chips or smaller 74LS chips depending on performance needs.
29:02 Technology Mapping for 74 Series Logic: Special technology mapping steps in Yosys handle mapping complex logic elements like adders and counters to combinations of 74 series chips.
32:04 Verification through Simulation: Post-synthesis simulation is crucial to verify the functionality of the generated 74 series logic circuit matches the original HDL code.
32:25 PCB Generation with Skidl: The Python library Skidl is used to automatically generate PCB layouts (KiCad netlists) from the synthesized 74 series logic circuit.
35:04 Combining Spreadsheet and 74 Logic Synthesis: Pepijn demonstrates the possibility of combining both approaches by generating Verilog from a spreadsheet and then synthesizing that Verilog into a 74 series logic circuit.
35:58 Future Directions: Expanding the spreadsheet-to-hardware capabilities, exploring the synthesis of more complex CPUs (like RISC-V) to 74 logic, and encouraging others to experiment with open-source tools are highlighted as future directions.