Core messages with semantic_id

[tridge (Andrew Tridgell)]

Following on from my semantic_id proposal, here are some illustrative messages.

Port type safety enforcement

Here is another idea. We have several reserved bits in the current v1 beta spec that are reserved. Here is the current packet format: [image] Bit 23 is marked as discard if bit isn’t 1. We could change that to be that when bit 23 is 0 the subject ID is used as a semantic ID. Then we’d have DSDL like this: # GNSS message @semantic_id 17 uint3 instance uint3 status uint32 time_week_ms uint16 time_week int36 latitude int36 longitude float32 altitude float32 yaw uint16 hdop uint16 vdop uint8 n…

GNSS

@semantic_id 1

uint3 instance
uint3 status
uint32 time_week_ms
uint16 time_week
int36 latitude # in 1e-8 degrees
int36 longitude # in 1e-8 degrees
float32 altitude
float32 yaw
uint16 hdop
uint16 vdop
uint8 num_sats
float32 velocity[3]
float16 speed_accuracy
float16 horizontal_accuracy
float16 vertical_accuracy
float16 yaw_accuracy

Magnetometer message

@semantic_id 2
uint3 instance
int16 field_mgauss[3] # in milliGauss

Barometer message

@semantic_id 3
uint3 instance
float32 pressure # Pa
int16   temperature_cdeg # centidegrees C

Differential pressure

@semantic_id 4
uint3 instance
float32 diff_pressure # Pa
int16   temperature_cdeg # centidegrees C

[scottdixon]

Heh, posts passed in the night. I just replied to your other post on this:

Port type safety enforcement

Noooooooo! Not our precious reserved bit!?! @kjetilkjeka, Andrew wants our reserved bit! Do you have any idea how hard we fought @pavel.kirienko to get that bit? Seriously though, I think the idea of just having a smattering of fixed port identifiers as part of a super-simple profile is the best way forward and I really don’t want to touch the UAVCAN V1 core specification to make this work (while I don’t expect to use UDRAL I also don’t want it to conflict with other profiles I will …

[scottdixon]

So, joining our two proposals would not require the reserved bit (just carve off a small semantic address space in UAVCAN) and add alternates:

@semantic_id 4
@alternate_semantic_id_0 5
@alternate_semantic_id_1 6

Now if a bad actor steps on a given port identifier the system integrator can manually (and grumpily) deconflict other sensors then go post negative reviews online about the part she purchased:

two stars, would not buy again. Used the same UAVCAN port identifier as the GNSS message my Acme MegaStar receiver sends. I had spent two hours on the phone with their terrible tech support to get it to work!