AP_RangeFinder: ensure that too low and too far states are propagated in DroneCAN

[andyp1per]

The current code means that you will always get "No Data" (which is fatal) rather than too low (which happens when you are sitting on the ground).

[peterbarker]

Could you refactor this for early-return, please?

I think it may also be amenable to a switch but only 30% sure

[rmackay9]

It's an existing issue so not a blocker but I think it would be good to put comments in the AP_RangeFinder_DroneCAN.h file beside the internal variables (e.g. _status) to clarify that these are the values received from the sensor. maybe it's just me but I find it quite confusing to have set_status(_status).

[rmackay9]

I think that @peterbarker also suggested that we change the logic in the update() method to have early returns and/or a switch statement.

I think the logic could be:

• always update the distance with whatever is received from the sensor

Re the status:

1. if we haven't received an update in 500ms (or whatever) set_status to NoData
2. if the status from the sensor is NoData then we set status to NoData (e.g. the sensor timed out)
3. if the status from the sensor is TooLow or TooHigh we set status to the sensor's status
4. if the status from the sensors is Good then we compare the distance to the min/max parameters and if it's out-of-range then we set status to TooLow or TooHigh appropriately. otherwise we set status to Good.

[andyp1per]

I think that @peterbarker also suggested that we change the logic in the update() method to have early returns and/or a switch statement.

Fixed

I think the logic could be:

* always update the distance with whatever is received from the sensor

Yes, but in this case the distance we have received is "TooLow" the only thing we can then usefully set it to is 0

Re the status:

1. if we haven't received an update in 500ms (or whatever) set_status to NoData

2. if the status from the sensor is NoData then we set status to NoData (e.g. the sensor timed out)

3. if the status from the sensor is TooLow or TooHigh we set status to the sensor's status

Fixed these

4. if the status from the sensors is Good then we compare the distance to the min/max parameters and if it's out-of-range then we set status to TooLow or TooHigh appropriately.  otherwise we set status to Good.

This was already happening

[peterbarker]

This is a really good fix.

Let's make sure we get this in for 4.7....

[peterbarker]

One this change is made my only question will be, "has it been tested in its current form?"

[tridge]

@andyp1per should set new_data on all types of new data from device

[peterbarker]

LGTM. Can be merged after testing

[tridge]

@andyp1per looks good to me, thanks for the changes! just needs testing

[peterbarker]

7:19 PM]Andy Piper: ok tested
[7:19 PM]Andy Piper: interestingly this device just returns 0 when too low
[7:20 PM]Peter Barker: So long as the flag is set 🙂

Approved now