SimDevice Types for CAN Wrapping HALSIM Library

[azaleacolburn]

Hi, I am an intern at Autodesk working on Synthesis, an FRC robot simulator for Fusion CAD exports. We're working on a code simulation system, where users can run their code on a robot being simulated in Synthesis. We're doing this with the WPILib HalSim WebSocket specification, where the robot code runs on a device and it gets piped over a WebSocket connection to Synthesis, which can also send back necessary sensor data. This was trivial for PWM devices, but we quickly found that critical CAN vendor devices didn't support simulation via the specification, so we decided to create a library of our own custom device wrappers that inherit from the device they enable simulation for, called SyntheSim.

Important

Some vendor CAN devices such as the TalonFX do support simulation via websockets, just not following the CANMotor specification. They don't send over the data we need.

We are doing this using the SimDevice class which is used by our custom device classes that extend the CAN devices we are offering simulation support for, in accordance with the HALSim WebSocket Specification.

The question we have is how to change the device type field in the WebSocket messages sent by the SimDevice. PWM and some CAN devices, such as the TalonFX which supposedly use the SimDevice class for their simulation support, show us as CANMotor or PWM devices in the type field of the sent data, while our custom class implementations (that inherit from the real vendor-managed devices) using the SimDevice class, appear as "SimDevices". We were wondering if there's a way to change this and make them send their type as CANMotor or CANEncoder for example.

Notice how the vendor devices show up as having the type "PWM" or "CANMotor", while our custom devices (distinguished by their adherence to the WS spec and the "SYN" keyword) show up as "SimDevices", with the notable exception of the SparkMax, which shows up as a SimDevice. The conclusion we came to is that either these's some way of specifying the device type for SimDevices that the PWM and TalonFX motors use, or only the SparkMax and our devices are using the SimDevice class for motor support, while TalonFX and Spark (The one unnamed PWM device) use either some other method of setting their type or don't use the SimDevice class at all.

We need to send over type information to determine how to simulate them in Synthesis. Note that this is a separate field from device, which is needed to construct a SimDevice and is just the arbitrary device name you give it and motor's deviceId (At least for SimDevices). We could work around this by creating a specification for the device field, which includes the device type, but properly including the device type in the correct field, without any additionally parsing of the device field being necessary, would be helpful for anyone else who wants to use our library to simulate unsupported vendor devices theirself.

Does anyone have any insight into how vendors are supposed to set the sent simulated device type?

[azaleacolburn]

So it turns out that WPILib gets the type and id (which is sent over the WebSocket connection as the device field) by splitting the name you pass in when constructing the SimDevice by the delimiter ":". So all we need to do is adhere to the particular naming convention of "[DeviceType]:[DeviceName]" and then the DeviceId gets tacked on there as well by WPILib. For example: "CANMotor:CANSparkMax[1]"

Function found here
We couldn't find this anywhere in documentation, it was discovered by @HunterBarclay while he was perusing the WPILib codebase.

[PeterJohnson]

It's documented here: https://github.com/wpilibsuite/allwpilib/blob/main/simulation/halsim_ws_core/doc/hardware_ws_api.md#can-messages