RISC-V User-Space Network Stack

Custom DPDK PMD · F-Stack port · FPGA NIC

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What I Built

A kernel-bypass network stack for RISC-V: a custom DPDK Poll Mode Driver for an FPGA NIC, patches to run F-Stack (FreeBSD networking) on RISC-V, and the tooling to cross-compile and deploy it. The driver maps MMIO directly into user space, implements burst RX/TX with descriptor rings and doorbell semantics, and fixes a RISC-V weak-memory-ordering bug with explicit fence instructions so the NIC sees updated descriptors correctly.

Layer	What I Did
PMD	Ported kernel NIC driver → DPDK burst API; added fence ow,ow / fence i,r where needed
F-Stack	RISC-V context-switch asm (arch_ctx.S), single-process init fixes, FreeBSD header glue
Build	Meson cross-file for riscv64-linux-gnu; tuned f-stack.conf and nginx.conf

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Tech Stack

C · DPDK · F-Stack · FreeBSD · RISC-V · Meson · vfio-platform · MMIO · AXI DMA

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Architecture

┌──────────────────────────────────────────────────────────────────────────┐
│                     RISC-V FPGA Host                                      │
├──────────────────────────────────────────────────────────────────────────┤
│                                                                           │
│   Nginx / App                                                             │
│        │                                                                  │
│        ▼                                                                  │
│   F-Stack (libfstack)  ◄──  RISC-V port: arch_ctx.S, ff_dpdk_if patches   │
│        │                                                                  │
│        ▼                                                                  │
│   DPDK EAL  ◄──  Custom PMD: eth_rx_burst, eth_tx_burst, doorbell, fence  │
│        │                                                                  │
│        ▼                                                                  │
│   FPGA NIC (MMIO · AXI DMA Scatter-Gather)                               │
│                                                                           │
└──────────────────────────────────────────────────────────────────────────┘

Highlights

Component	Description
Custom PMD	Burst RX/TX, 1024-entry descriptor rings, tail-pointer doorbell, DMA error handling
RISC-V memory fix	fence ow,ow / fence i,r so NIC observes correct descriptor state (weak ordering)
F-Stack port	Context-switch asm for micro-threading; single-process mode fixes
Cross-build	riscv64-linux-gnu toolchain via Meson cross-file

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Project Structure

Path	Role
COMPAS_PMD/	Custom DPDK PMD source
FSTACK_RISCV_PORT/	F-Stack + FreeBSD RISC-V patches
riscv_cross.txt	Meson cross-compilation profile
f-stack.conf	Runtime config (lcore mask, PCI whitelist)
nginx.conf	Nginx + F-Stack affinity config
RISCV_FLASHING.md	FPGA flashing & serial console (env-specific)

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Quick Start

1. Integrate the driver

cp -r COMPAS_PMD/drivers/net/compas /path/to/dpdk/drivers/net/
meson setup build --cross-file riscv_cross.txt -Ddrivers=net/compas
ninja -C build

2. Patch F-Stack

cp -r FSTACK_RISCV_PORT/* /path/to/f-stack/
cd /path/to/f-stack/lib && ./setup_freebsd_riscv.sh
# Build libfstack with riscv64-linux-gnu toolchain

3. Run

• Program FPGA, connect to RISC-V console (see RISCV_FLASHING.md)
• Deploy f-stack.conf and nginx.conf
• ./nginx -c nginx.conf

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License

MIT — see LICENSE.