Zephyr Connectivity: USB & CAN

Build versatile hardware interfaces using Zephyr's modular USB device stack and robust CAN controller support.

Core Workflows

1. USB Device Stack

Configure and enable standard USB classes for host communication.

• Reference: usb_device_stack.md
• Key Tools: CONFIG_USB_DEVICE_STACK, usb_enable(), CDC ACM, HID.

2. USB-to-CAN Integration

Implement high-performance bridge patterns for CAN bus diagnostics and adapters.

• Reference: usb_to_can.md
• Key Tools: can_send(), k_msgq, binary packetization, CAN filtering.

Quick Start (USB CDC ACM)

# prj.conf
CONFIG_USB_DEVICE_STACK=y
CONFIG_USB_CDC_ACM=y

#include <zephyr/usb/usb_device.h>

void main(void) {
    usb_enable(NULL);
}

Professional Patterns (Adapter Design)

• Binary Protocols: Use established protocols like gs_usb for robust data transfer over the USB-to-CAN bridge.
• Hardware Filtering: Rely on the CAN controller's hardware filters to minimize CPU overhead from irrelevant bus traffic.
• Thread Safety: Use Zephyr's kernel IPCs (k_msgq, k_fifo) to safely move data between high-priority CAN interrupts and the USB processing thread.

Automation Tools

• can_filter_lint.py: Validate CAN filter ID/mask tables from CSV.

Examples & Templates

• can_filters_template.csv: Starter CAN filter table for adapter firmware.

Validation Checklist

• USB enumeration succeeds and the host sees the expected class interface.
• CAN frames can be transmitted and received on a known-good test bus.
• Bridge buffering prevents frame loss under burst traffic conditions.
• Protocol framing between USB endpoint and CAN payload is decoded consistently on both sides.

Resources

• References:
  • usb_device_stack.md: Configuring USB classes and descriptors.
  • usb_to_can.md: Adapter patterns and buffering strategies.
• Scripts:
  • can_filter_lint.py: CAN filter table consistency checker.
• Assets:
  • can_filters_template.csv: Sample filter definitions.