Nextpnr‐Himbaechel Gowin

This guide covers the important command-line options for using nextpnr-himbaechel with Gowin FPGAs.

Essential Options

Basic Usage

nextpnr-himbaechel --json input.json --write output.json --device <device-part> --vopt cst=<board>.cst [options]

Required Options

• --json <file>: Input JSON design file from Yosys
• --write <file>: Output JSON file for the placed and routed design
• --device <part>: Target FPGA part number (e.g., GW1N-LV1QN48C6/I5)
• --vopt cst=<file>: Specify the constraint (.cst) file for pin mappings (Required)
  • All top-level ports must be assigned in the CST file
  • Unassigned top-level ports will cause an error
  • CST files are typically provided with board documentation

Important Architecture Options

• --vopt family=<family>: Specify the FPGA family (Required for certain devices)

Examples by Board Family

Devices Requiring Family Option

Board	Device	Family
Tang Nano 20K	GW2AR-LV18QN88C8/I7	GW2A-18C
Tang Primer 20K	GW2A-LV18PG256C8/I7	GW2A-18
Tang Nano 9K	GW1NR-LV9QN88PC6/I5	GW1N-9C
SZFPGA	GW1NR-LV9LQ144PC6/I5	GW1N-9
Trenz TEC0117	GW1NR-UV9QN88C6/I5	GW1N-9

nextpnr-himbaechel --json design.json \
                   --write output.json \
                   --device $DEVICE \
                   --vopt family=$FAMILY \
                   --vopt cst=$BOARD.cst

Standard Devices

Board	Device
Tang Nano	GW1N-LV1QN48C6/I5
Tang Nano 1K	GW1NZ-LV1QN48C6/I5
Tang Nano 4K	GW1NSR-LV4CQN48PC7/I6
Runber	GW1N-UV4LQ144C6/I5

nextpnr-himbaechel --json design.json \
                   --write output.json \
                   --device $DEVICE \
                   --vopt cst=$BOARD.cst

Family Option Details

The --vopt family=<family> option is required for certain device families where Gowin has produced silicon variants with identical part numbers. The presence of a 'C' in the device's date code indicates a silicon variant that requires explicit family specification.

For example, GW2A and GW1N-9 devices may require different family options based on silicon variants:

1. GW2A Series:

   # For non-C variant
   --vopt family=GW2A-18
   # For C variant
   --vopt family=GW2A-18C

2. GW1N-9 Series:

   # For non-C variant
   --vopt family=GW1N-9
   # For C variant
   --vopt family=GW1N-9C

Additional Options

Placement and Routing

• --placer <algorithm>: Choose placer algorithm (sa, heap; default: heap)
• --router <algorithm>: Choose router algorithm (router1, router2; default: router1)

Debug and Visualization

• --placed-svg <file>: Generate SVG visualization of placement
• --routed-svg <file>: Generate SVG visualization of routing
• --report <file>: Write timing and utilization report in JSON format

Flow Control

• --pack-only: Only pack the design without placement/routing
• --no-route: Skip routing stage
• --no-place: Skip placement stage

Common Issues

1. Missing Family Option: If you get an error message about needing to specify the family for GW2A or GW1N-9 series, check your device's marking for a 'C' variant and add the appropriate family option.

2. Missing or Incorrect CST File:

   • Each top-level port in your design MUST be assigned to a physical pin in the CST file
   • Unassigned ports will cause errors
   • Make sure you're using the correct constraints file for your board
   • CST files are typically provided with board documentation or example projects

Notes

• The chipdb (internal device database) is automatically selected based on the device and family options.
• For the most accurate results, ensure you're using the latest version of nextpnr-himbaechel.
• Reference your board's documentation for the correct CST file and pin assignments.