Chestnut – eGPU dock with open-source firmware
Comma.ai's new 'Chestnut' eGPU dock boasts open-source firmware for its USB4-to-PCIe bridge chip. This breakthrough offers hardware enthusiasts unprecedented transparency and control over a component traditionally opaque in eGPU enclosures. While designed to power larger driving models in cars, its hackable nature is generating buzz among those keen on deep technical dives and hardware exploration.
The Lowdown
Comma.ai, led by George Hotz, has launched "Chestnut," an eGPU dock that stands out by offering open-source firmware for its USB4-to-PCIe bridge chip. Initially developed to enhance compute power for comma.ai's self-driving openpilot system, Chestnut represents a significant departure from the typically closed-source nature of eGPU hardware, providing a hackable platform for those interested in deeper hardware control.
- The Chestnut dock is built around an ASMedia ASM2464PD chip, bridging PCIe Gen4 x4 to USB4, with its C source firmware openly available on GitHub under the tinygrad organization.
- It comes in two configurations: the "Tiny chestnut" dock-only for $249, or the "Chestnut ready to drive" package for $799, which includes an AMD Radeon RX 9060 8GB GPU, cabling, and mounting hardware.
- Comma.ai's primary motivation was to increase the computational headroom for its openpilot system, moving from a 10W on-device budget to approximately 100W, enabling the deployment of a new 1B-parameter driving model in openpilot 0.11.2.
- For general PC users and hardware enthusiasts, the open firmware is a game-changer; unlike traditional eGPU enclosures with opaque bridge silicon, Chestnut allows users to audit, debug, and even reflash the controller.
- While not designed for maximum gaming throughput, the open firmware provides a debug and control plane, allowing access to PCIe TLPs (albeit slowly at 3.6 MB/s write, 1.8 MB/s read) and faster DMA access to the chip's SRAM (700 MB/s).
- Caveats include the inherent bandwidth limitation of Gen4 x4 over USB4 compared to native PCIe x16, and comma.ai's focus on automotive applications rather than supporting it as a general PC peripheral.
Despite its origins in automotive AI and its modest price point, the Chestnut dock's open-source firmware makes it a uniquely interesting piece of hardware, offering unprecedented transparency and control to a segment of the computing ecosystem that has long been opaque.