Fix ANT command status response (page 71)

[switchabl]

The handling of page 71 command status pages is broken. The data bytes need to be the raw bytes from the control command, but we are trying to pass floats instead, causing FortiusANT to crash (#101 (comment)). Also the max value for the sequence # should be 254, as 255 indicates no command received [0]

Awaiting confirmation from @smithnb that this indeed fixes the issue.

[0] Section 8.12.3 of ANT+ FE specification

[WouterJD]

Some questions:

1

info[8] is unpaged by msgUnpage48_BasicResistance()

p71_Data4 = info[8]
could be replaced by
p71_Data4 = Grade

2

Please add comment # rollover at 254, as 255 indicates no command received
Should the intial p71_SequenceNr = 0 be p71_SequenceNr = 255 for the same reason?

3

p71_Data3 =  int(TacxTrainer.TargetPower) & 0x00ff
p71_Data4 = (int(TacxTrainer.TargetPower) & 0xff00) >> 8

is replaced by

p71_Data3                   = info[7]
p71_Data4                   = info[8]

although it should be the same
TacxTrainer.SetPower(ant.msgUnpage49_TargetPower(info))
could better be split into

TargetPower = ant.msgUnpage49_TargetPower(info))
TacxTrainer.SetPower(TargetPower)

and then TargetPower be used, in analogy with Grade above

4

Like previous; I think the result is the same:

p71_Data2                   = WindResistance
p71_Data3                   = WindSpeed
p71_Data4                   = DraftingFactor

Or do I miss the essential for 3 and 4?

[switchabl]

1, 3, 4: The unpage functions do unit conversions too. So TargetPower is actually info[7-8] / 4. In that case it just means that we are sending the wrong value back. And e.g. WindResistance is

    WindResistance = tuple[nWindResistanceCoefficient]
    if WindResistance == 0xff:
        WindResistance = 0.51
    else:
        WindResistance = WindResistance * 0.01 # kg/m

So we are trying to pass a float (which is what causes the crash). I don't particularly like accessing info directly but I don't see a good alternative here (short of moving the unit conversion code out of unpage). Trying to reverse the calculation will not work in all cases and it is also really messy. In any case it ensures that we are really sending back the same raw bytes that we received (which is what is required). So I could maybe just add comments saying that 1) the raw bytes are expected by the CTP and 2) what they contain?

2: Yes, good catch. Also I will add a comment.

[WouterJD]

@switchabl agree; plse check for consistency👍

[switchabl]

Hopefully everything is consistent and comments are clear now. Let me know if there is anything else.

[WouterJD]

Thanks and done