标签：#ros2

This is a writeup of building a required CI gate for degraded-network behavior. The system under test is a robotics fleet substrate, but the finding applies to anyone shaping networks in CI. Ganglion exists to reach robots on networks nobody controls. Warehouse Wi-Fi, carrier CGNAT, a hospital VLAN, a customer firewall that was configured once in 2019 and has not been touched since. Until this week that claim was a sentence on a website. CI ran on clean loopback, everything was green, and the failure modes that actually matter in the field were the exact ones the test suite could never produce. That is now a required gate. Every push to main runs the full deploy, invoke and verify round trip over the relay against five shaped network profiles, and all five have to pass before anything merges. I build Ganglion, so treat the enthusiasm accordingly. The part worth your time is not that it went green. It is what I got wrong on the way there. The five profiles clean : baseline, no shaping. If this one fails, something else is broken. lossy : packet loss with light reordering. high-latency : 250ms round trip. asymmetric : plentiful downlink, starved uplink. This is the one nobody tests and the one teleop actually dies on, because control acknowledgements go the starved direction. nat-relay : endpoints with no route to each other at all, forcing hole punching to fail and relay fallback to carry the session. The last two are the ones I care about. Loss and latency are what people imagine a bad network is. Asymmetry and no-direct-route are what a bad network usually is. What I got wrong The original design assumed you can pin netem's seed and get a repeatable lossy run. Two profiles: a pinned-seed one that gates the build, and a nastier randomized one that runs nightly and is allowed to fail. You cannot pin netem's seed. Its loss and jitter draw from the kernel RNG and there is no seed parameter to set. A "deterministic lossy netem profile" is not a thing that exists. This m

If you have ever built an autonomous mobile robot, you have likely run into the dreaded "Shuffled USB Port" problem. You boot up your robot, fire up your ROS 2 launch files, and... crash. Your LiDAR driver is trying to parse data from your IMU, and your IMU node is screaming about invalid serial frames. Because Linux assigns virtual serial paths like /dev/ttyUSB0 and /dev/ttyUSB1 based purely on which device initialized milliseconds faster, relying on default OS paths is a recipe for system instability. When you are scaling up to dozens of Jetson Orin nodes —each equipped with an RPLIDAR C1 and a Yahboom 10-axis IMU —manually hardcoding paths or writing rigid scripts on every individual machine isn't viable. Here is how production-grade robotics fleets handle plug-and-play USB binding dynamically using configuration-driven udev rules. The Core Concept: Vendor ID vs. Physical Port vs. Serials Linux's udev (device manager) allows us to dynamically create stable symbolic links (symlinks) like /dev/rplidar and /dev/imu when hardware is plugged in. How we identify those devices determines our fleet's flexibility: USB Serials: Unique to each individual chip. Highly secure, but requires registering every single replacement sensor in your codebase. Physical USB Ports ( KERNELS ): Tied to a physical slot on the carrier board. Great if you have identical sensors, but forces technicians to plug cables into highly specific, undocumented ports. Vendor ID (VID) & Product ID (PID): Identifies the USB-to-serial converter chip on the sensor board. Because the RPLIDAR C1 uses a Silicon Labs CP210x chip ( 10c4:ea60 ) and the Yahboom IMU uses a QinHeng CH340 chip ( 1a86:7523 ), they use completely distinct silicon. This means we can map them dynamically and reliably using just their VID/PID —allowing field technicians to plug them into any USB port on the Jetson without breaking the system. Step 1: The Configuration-Driven File ( devices.conf ) Hardcoding vendor rules inside shell scri