Filip Filmar

I am a software engineer at Google. In my own time I build programmable hardware, and the build systems around it. Most of that work is open source, and I write about it on hdlfactory.com.

This page lists my public work from October 2025 to October 2026.

Hardware and RISC-V

• TxHDL is a hardware description language written as a Rust library, built with Dragiša (dj3maj). A design is ordinary async Rust, and the library lowers it to Verilog and VHDL.
  • Vreteno is the RV32IMAC RISC-V core written in it. It runs at 100 MHz on an Artix-7 board with 1 GiB of DDR3. Mainline Linux boots on it to a BusyBox shell, with virtual memory on, and Doom runs on it with HDMI output.
  • Razboj is a minimal GPU in about a hundred lines of TxHDL. It reads a display list and draws rectangles and triangles into a framebuffer.
  • vreteno-conformance runs RISC-V International's architectural tests (ACT4) on the newest core every day. The Sail reference model checks each result, and each daily report is published as a PDF.
• Cocoapuffs is a RISC-V system on chip on the same Artix-7 board, built around the 64-bit NOEL-V core. Fuchsia's Zircon kernel boots on it end to end, from OpenSBI to userspace.
• wdbcvt reads Vivado's waveform database (.wdb), a format AMD does not document. It converts the files to FST and SQLite, and handles over 95% of the format's features, as measured on behavioral VHDL, Verilog and SystemVerilog.

Bazel for programmable hardware

I build FPGA designs with Bazel, from the toolchain up, so that a fresh machine builds a bitstream with one command.

• rules_vivado runs AMD Vivado synthesis, place and route, and programming as Bazel actions. toolchains_vivado installs Vivado itself as an ephemeral toolchain.
• rules_openxc7 does the same for 7-series parts with the open toolchain: Yosys, nextpnr-xilinx and Project X-Ray. It uses the rule names of rules_vivado, so a project switches between the two by changing one load line. I measured the build times of the two side by side.
• Simulation and libraries: rules_nvc, toolchains_nvc, toolchains_verilator, rules_vunit, rules_osvvm, grlib (Gaisler's GRLIB and NOEL-V), and rules_ghdl, where I merged 27 changes in that period.
• Firmware: rules_opensbi, rules_dtc and a bare-metal RISC-V GCC toolchain.

Hermetic builds

A hermetic build uses only tools it fetched itself, pinned by checksum, and nothing installed on the host.

• bazel_local_nix brings Nix packages into a Bazel build with no Nix installed on the host. It runs an ephemeral Nix, unprivileged, in a bubblewrap sandbox.
• bazel_rootfs and xrootfs give a build a pinned Debian root file system, taken from an OCI image.
• bazel-bats, bazel-ebook, rules_shar, rules_latex_host, bazel_graphviz and gotopt2 are smaller rule sets and tools.

In that period I published 43 module releases to the Bazel Central Registry, across the rule sets above.

Contributions to other projects

• google/rust_icu, the Rust bindings for ICU, which I maintain: 52 merged changes in that period. I moved the build to Bazel, added ICU 74 to 77, and automated the releases. I also fixed two memory safety bugs in message formatting: a read past the end of the arguments, and strings passed without a terminating null.
• Smaller fixes: a universal macOS binary for the rain BitTorrent client, support for the Alinx AX7A200B board in fusesoc/blinky, and a documentation fix in uber/hermetic_cc_toolchain.

Other projects

• synod is a Paxos agent in Go. It keeps a key-value store in agreement across peers that join at any time.
• mkill watches memory use. When memory runs low, it stops the program whose use grew fastest, before the kernel's out-of-memory killer has to act.
• chrome-auto-reload is a Chrome extension that reloads a tab on a timer. It has no access to page content and makes no network requests.

Writing

I published 38 articles on hdlfactory.com since October 2025. A selection:

• TxHDL: a hardware description language is just a Rust async runtime
• Linux boots to a shell on Vreteno
• Doom on a RISC-V core written in TxHDL
• Booting Fuchsia's Zircon on a homebrew RISC-V SoC, on an Artix-7 FPGA
• Bazel all the way down: how I build programmable hardware
• My homelab is fully ephemeral
• The FPGA hardware interview: a topic guide with questions and exercises
• Fuchsia Internals, a report series for hardware engineers: Vol. I, graphics and display, and Vol. II, the build system and toolchains.
• Thanklessly Maintaining Open Source Software, a short humor book about a year in the life of a maintainer.

Skills

• Languages: Rust, Go, C++, Python, Starlark, shell, VHDL, Verilog and SystemVerilog.
• Hardware: AMD 7-series FPGAs, Vivado, Yosys and nextpnr, Verilator, NVC and GHDL, RISC-V cores and boot chains (OpenSBI, Linux, Zircon).
• Build and operations: Bazel and bzlmod, Nix, Kubernetes, GitHub Actions and Forgejo Actions.

Also

I am a licensed real estate agent in California. My real estate site is re.filmar.us.

Contact

• Website: hdlfactory.com
• GitHub: filmil
• LinkedIn: in/filmil