Re: How to get raw data from gpsd?

[张延涛]

Hi Gary!

I hope this finds you well.

I regret to inform you that after discussing with the chip manufacturer, it appears that the raw data format of ALLYSTAR is considered confidential in commercial terms and is not available for public access. Therefore, we are unable to obtain any related protocol manuals.

What is known is that the binary data outputted by ALLYSTAR begins with 0xF1D9 and ends with 0x0D0A. Hence, gpsd can filter out the binary data of ALLYSTAR according to this rule.

Furthermore, through several experiments, I've found that if ALLYSTAR outputs an excessive amount of raw data too quickly (approximately 30KB of hexadecimal data per second), gpsd tends to drop some bytes of data approximately every 2 minutes and 30 seconds.

Best regards,
Yantao Zhang

Gary E. Miller <gem@rellim.com> 于2024年4月2日周二 03:52写道：

Yo 张延涛!

On Mon, 1 Apr 2024 19:04:57 +0800
张延涛 <zh6tao@gmail.com> wrote:

> > Can you get me documentation on the binary protocol? 
>
> I'm sorry, we are unable to obtain the protocol documentation from
> the GNSS chip manufacturer as well.

That will be a problem.  I did find a little documentation.

https://docs.datagnss.com/rtk-board/files/datasheet/01_Module/Common%20command/T-5-2010-Common%20Commands%20Exclusive%20to%20Allystar-V1.0.pdf

https://docs.datagnss.com/rtk-board/files/T-5-1908-001-GNSS_Protocol_Specification-V2.3.pdf

> In our current operations, we
> only need to provide an interface to the chip manufacturer, enabling
> them to retrieve raw data through this interface.

The you do not need gpsd.

> Once the chip
> manufacturer receives the raw data, the specific parsing rules are
> left to them to handle. *It would be great if you could add an
> interface to gpsd that allows for the retrieval of completely raw
> data!*

Not going to happen.  The point of gpsd is to filter out junk,
when autobauding there is a very large amount of junk.  With no
documentation, your data stream looks the same as junk.

However, with the above doc, I did add a skeleton ALLYSTAR driver to git
head.  And found out your data stream is junk.  Most, but not all, of the
ALLYSTAR messages have bad checksums.  Enough are good that I know my
skeleton driver is working.

> > Can you build gpsd from git head and test? 
>
> Yes, I can compile gpsd from the git head and write test programs.

Then please grab a copy of the current git head and see how that
works for you.

> >  Do you have sample parts you can send me? 
>
> Regarding your request for sample parts, raw data is essentially a
> black box for us as well. Therefore, we don't have any samples to
> provide for your reference.

If I have parts, I can figure out the black box, and I have enough doc
to decode most messages.  You help me, I help you.

RGDS
GARY
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