Questions about UAVCAN v1 FAQ

pepe · September 6, 2021, 12:15pm

Hello Kalyan,

I am quite new to UAVCAN and still trying to get my feet wet. I have a some of questions:

Is there any up to date document for the UCANPHY or the V0 is still the latest one. I assume in terms of hardware, while still working with CAN not much has changed.
Are there any V1 tutorial on how to implement dynamic Node IDs?

Many thanks,
Pepe

pavel.kirienko · September 6, 2021, 12:22pm

I am not Kalyan but I think I can answer these.

The latest UCANPHY draft is available here: https://forum.opencyphal.org/uploads/short-url/9ohIXmOudLBXUFxOWRJ1YtJBv3Z.pdf. There are no pending changes on the roadmap. I expect the document to be released pretty much unchanged.
The PnP mechanism is implemented in the official demos (be sure to read the README for a detailed guidance):

github.com

OpenCyphal-Garage/demos/blob/bfdbae036bab4cd389f567127fbd7640021c7e28/differential_pressure_sensor/src/main.c#L228-L249

      
        
            // Note that this will only work over CAN FD. If you need to run PnP over Classic CAN, use message v1.0.
            uavcan_pnp_NodeIDAllocationData_2_0 msg = {0};
            msg.node_id.value                       = UINT16_MAX;
            getUniqueID(msg.unique_id);
            uint8_t      serialized[uavcan_pnp_NodeIDAllocationData_2_0_SERIALIZATION_BUFFER_SIZE_BYTES_] = {0};
            size_t       serialized_size = sizeof(serialized);
            const int8_t err = uavcan_pnp_NodeIDAllocationData_2_0_serialize_(&msg, &serialized[0], &serialized_size);
            assert(err >= 0);
            if (err >= 0)
            {
                const CanardTransfer transfer = {
                    .timestamp_usec = monotonic_time + MEGA,
                    .priority       = CanardPrioritySlow,
                    .transfer_kind  = CanardTransferKindMessage,
                    .port_id        = uavcan_pnp_NodeIDAllocationData_2_0_FIXED_PORT_ID_,
                    .remote_node_id = CANARD_NODE_ID_UNSET,
                    .transfer_id    = (CanardTransferID) (state->next_transfer_id.uavcan_pnp_allocation++),
                    .payload_size   = serialized_size,
                    .payload        = &serialized[0],
                };

This file has been truncated. show original

Also, see PyUAVCAN docs for the server-side implementation: https://pyuavcan.readthedocs.io/en/stable/api/pyuavcan.application.plug_and_play.html

Nitpick: don’t say “dynamic node-ID allocation”, the correct term is “plug-and-play node-ID allocation” because node-IDs do not change at runtime, they are auto-configured once and kept unchanged, kind of like DHCP addresses.

pepe · September 6, 2021, 12:31pm

Many thanks for the information, I will look into the docs and will try to make a proof of concept and share it in the appropriate thread.

coder_kalyan · September 7, 2021, 2:46pm

Thanks for answering Pavel! @pepe feel free to let us know if you have any other questions, including something you find unclear that I should put in the FAQ