rwhitby/nextpnr-xilinx

Experimental flows using nextpnr for Xilinx devices

nextpnr-xilinx

nextpnr is a open-source multi-architecture place-and-route framework aimed at real-world FPGA silicon. This is an experiment to integrate nextpnr with RapidWright, an open interface into Xilinx FPGAs, and Project Xray, open bitstream documentation for xc7 FPGAs.

Currently two flows are supported:

• UltraScale+ with RapidWright database generation, bitstream generation using RapidWight and Vivado
• xc7 with Project Xray database generation, bitstream generation using FASM and Project Xray (no Vivado anywhere in the flow)

Prerequisites - UltraScale+

• Follow the RapidWright manual install instructions
• Make sure $RAPIDWRIGHT_PATH is set correctly for all further steps
• Download a JAR of recent GSON
• Download and build Project Xray
• Install yosys

Prerequisites - Artix-7

• Run git submodule init and git submodule update to fetch the database and metadata
• Download and build Project Xray
• Install yosys

A brief (academic) paper describing the Yosys+nextpnr flow can be found on arXiv.

Building - Artix-7

• Run cmake -DARCH=xilinx .
• Run make (with -jN as appropriate)

Building - UltraScale+

• Run cmake -DARCH=xilinx -DRAPIDWRIGHT_PATH=/path/to/rapidwright -DGSON_PATH=/path/to/gson-2.8.5.jar .
• Run make (with -jN as appropriate)

Building the Arty example - XRay database

• Run pypy3 xilinx/python/bbaexport.py --device xc7a35tcsg324-1 --bba xilinx/xc7a35t.bba (regular cpython works as well, but is a lot slower)
• Run ./bbasm --l xilinx/xc7a35t.bba xilinx/xc7a35t.bin
• Set XRAY_DIR to the path where Project Xray has been cloned and built (you may also need to patch out the Vivado check for utils/environment.sh in Xray by removing this line and everything beyond it: https://github.com/SymbiFlow/prjxray/blob/80726cb73ba5c156549d98a2055f1ee3eff94530/utils/environment.sh#L52)
• Run attosoc.sh in xilinx/examples/arty-a35.

Building the zcu104 example - RapidWright

• Run java -jar rapidwright_bbaexport.jar xczu7ev-ffvc1156-2-e xilinx/constids.inc xilinx/xczu7ev.bba
• Run ./bbasm --l xilinx/xczu7ev.bba xilinx/xczu7ev.bin
• Run blinky.sh in xilinx/examples/zcu104.

Creating chip database from RapidWright

• Run java -jar rapidwright_bbaexport.jar xczu2cg-sbva484-1-e xilinx/constids.inc xilinx/xczu2cg.bba

  • This uses RapidWright to build a textual representation of a chip database for nextpnr
  • Replace xczu2cg-sbva484-1-e and the bba filename with the device you want to target. You can build multiple databases for multiple devices if desired (subject to the support caveats above)

• Run ./bbasm --l xilinx/xczu2cg.bba xilinx/xczu2cg.bin

  • This converts the text database from above to a binary database that nextpnr can mmap

• See xilinx/examples for example scripts that run the Yosys/nextpnr/RapidWright flow, then use Vivado to write a Verilog simulation netlist.

Notes

• Currently supported:

• xc7 and xcup: LUTs (including fractured), FFs, DRAM (only RAM64X1D), carry (XORCY and MUXCY or CARRY4), SRL16E and SRLC32E (no cascading), BRAM and IO

• xcup: OSERDESE3, ISERDESE3, IDDRE1, ODDRE1, IDELAYE3, ODELAYE3, IDELAYCTRL, BUFGCTRL, BUFG, BUFGCE, BUFG_PS, PLLE4_ADV, PLLE4_BASIC, MMCME4_ADV, MMCME4_BASIC, URAM288E, DSP48E2 (no cascading)

• xc7: OSERDESE2, ISERDESE2, IDELAYE2, IDELAYCTRL, BUFGCTRL, PLLE2_BASIC, PLLE2_ADV

• Bels, tile wires and pips are deduplicated but nodes (connections between tile wires) are not. This means that databases for larger devices will be several gigabytes in size (but significantly smaller than a fully flat database).