Re: Bug/Oversight in gatchat/gatresult.c with negative numbers

[Alex J Lennon <ajlennon@dynamicdevices.co.uk>]

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On 27/07/2021 15:38, Denis Kenzior wrote:
> Hi Alex,
>
> On 7/20/21 11:11 AM, Alex J Lennon wrote:
>> Hi all,
>>
>> I'm doing a bit of work with Ofono again, extending support for a 
>> Quectel EG91 - handling additional cell strength information which 
>> seems necessary for LTE.
>>
>> I'm using Quectel's AT+QCOPS which is returning some negative signal 
>> strengths and after some investigation I've spotted that 
>> gatresult::g_at_result_iter_next_number() doesn't handle negative 
>> numbers.
>
> AT commands do not have a concept of negative numbers.  v.250 Section 
> 5.3.1:
> <number> may be a string of one or more characters from "0" through 
> "9" representing a decimal
> integer value. Commands that expect a <number> are noted in the 
> description of the command (see
> clause 6).
>
> I don't recall any other vendor using negative values in AT commands.
>
> If you want to add a negative number parser to GAtChat, then please 
> make it a separate method, so that it is very clear that a vendor 
> 'extension' is being worked around.
>
> Regards,
> -Denis

Hi Denis,

I have been chasing this up with Quectel and they tell me this the 
correct implementation.

"QCOPS and QENG command show the RSSI、RSRP and SINR value of the 
network, this is in accordance with the 3GPP TS regulations, so it is 
normal for negative numbers to be displayed.image"

This is quite interesting as aside from the parsing, Ofono seems to rely 
on negative numbers being errors (e.g. src/netmon.c)

What are your thoughts? This being correct, one would have thought other 
modem manufacturers would report in the same manner.

Cheers,

Alex



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