* Andreas Kemnade <[email protected]> [231126 19:18]:
> So the main questions I see:
> - is the approach right to abandon drivers/misc/ti-st?
Yes.
> - Output at /dev/gnssX:
> AI2 vs. NMEA
> The chip can be configured into sending AI2-encapsulated NMEA,
> or proving data in a binary format.
> Some research has to be done yet for the details.
> A pile of logs is waiting for further analysis...
>
> Arguments for/against NMEA:
> + Userspace is prepared to handle it
> + Power management can be easily done by the kernel
> - Less functionality can be used.
I'd go with NMEA format as the default setting :)
> Arguments for/against AI2:
> + Full functionality can be accessed from userspace (incl. A-GPS,
> maybe raw satellite data)
> - Userspace has to behave to have proper power management
> - No freely (not even as in beer) tool available to fully use AI2,
> so there will be only a real advantage after long "French Cafe"
> sessions.
Seems AI2 could be optionally enabled as needed with some writes
to /dev/gnss0 to change the mode?
Regards,
Tony
Hi,
On Mon, 27 Nov 2023 15:54:24 +0200
Tony Lindgren <[email protected]> wrote:
[...]
> > - Output at /dev/gnssX:
> > AI2 vs. NMEA
> > The chip can be configured into sending AI2-encapsulated NMEA,
> > or proving data in a binary format.
> > Some research has to be done yet for the details.
> > A pile of logs is waiting for further analysis...
> >
> > Arguments for/against NMEA:
> > + Userspace is prepared to handle it
> > + Power management can be easily done by the kernel
> > - Less functionality can be used.
>
> I'd go with NMEA format as the default setting :)
>
yes, that would also be my preference.
> > Arguments for/against AI2:
> > + Full functionality can be accessed from userspace (incl. A-GPS,
> > maybe raw satellite data)
> > - Userspace has to behave to have proper power management
> > - No freely (not even as in beer) tool available to fully use AI2,
> > so there will be only a real advantage after long "French Cafe"
> > sessions.
>
> Seems AI2 could be optionally enabled as needed with some writes
> to /dev/gnss0 to change the mode?
Hmm, we have
/sys/class/gnss/gnss0/type to get the mode, maybe we add some file
to change the mode? Or having it hidden behing a module parameter
and implement something better accessible if any need arrives?
If we want NMEA output, probably some init commands will be sent at
open(), but userspace doing something with AI2 probably does not want
the device touched, so it should probably be already be set before open().
Regards,
Andreas
On Mon, Nov 27, 2023 at 2:51 PM Andreas Kemnade <[email protected]> wrote:
>
> Hi,
>
> On Mon, 27 Nov 2023 15:54:24 +0200
> Tony Lindgren <[email protected]> wrote:
>
> [...]
> > > - Output at /dev/gnssX:
> > > AI2 vs. NMEA
> > > The chip can be configured into sending AI2-encapsulated NMEA,
> > > or proving data in a binary format.
> > > Some research has to be done yet for the details.
> > > A pile of logs is waiting for further analysis...
> > >
> > > Arguments for/against NMEA:
> > > + Userspace is prepared to handle it
> > > + Power management can be easily done by the kernel
> > > - Less functionality can be used.
> >
> > I'd go with NMEA format as the default setting :)
> >
> yes, that would also be my preference.
>
> > > Arguments for/against AI2:
> > > + Full functionality can be accessed from userspace (incl. A-GPS,
> > > maybe raw satellite data)
> > > - Userspace has to behave to have proper power management
> > > - No freely (not even as in beer) tool available to fully use AI2,
> > > so there will be only a real advantage after long "French Cafe"
> > > sessions.
> >
> > Seems AI2 could be optionally enabled as needed with some writes
> > to /dev/gnss0 to change the mode?
>
> Hmm, we have
> /sys/class/gnss/gnss0/type to get the mode, maybe we add some file
> to change the mode? Or having it hidden behing a module parameter
> and implement something better accessible if any need arrives?
>
> If we want NMEA output, probably some init commands will be sent at
> open(), but userspace doing something with AI2 probably does not want
> the device touched, so it should probably be already be set before open().
Is there another revision coming or should I try to test this one? I
am not very familiar with the GNSS part of the module, but it sounds
like there was some consensus as to which direction we should go. I
should have a little time this weekend.
thanks
adam
>
> Regards,
> Andreas
>
On Mon, Nov 27, 2023 at 09:51:08PM +0100, Andreas Kemnade wrote:
> On Mon, 27 Nov 2023 15:54:24 +0200
> Tony Lindgren <[email protected]> wrote:
> > > - Output at /dev/gnssX:
> > > AI2 vs. NMEA
> > > The chip can be configured into sending AI2-encapsulated NMEA,
> > > or proving data in a binary format.
> > > Some research has to be done yet for the details.
> > > A pile of logs is waiting for further analysis...
Can you say something more about what the protocol looks like? Is there
some common framing that can/should be stripped by the driver in both
modes?
> > >
> > > Arguments for/against NMEA:
> > > + Userspace is prepared to handle it
> > > + Power management can be easily done by the kernel
> > > - Less functionality can be used.
> >
> > I'd go with NMEA format as the default setting :)
> >
> yes, that would also be my preference.
>
> > > Arguments for/against AI2:
> > > + Full functionality can be accessed from userspace (incl. A-GPS,
> > > maybe raw satellite data)
> > > - Userspace has to behave to have proper power management
> > > - No freely (not even as in beer) tool available to fully use AI2,
> > > so there will be only a real advantage after long "French Cafe"
> > > sessions.
> >
> > Seems AI2 could be optionally enabled as needed with some writes
> > to /dev/gnss0 to change the mode?
>
> Hmm, we have
> /sys/class/gnss/gnss0/type to get the mode, maybe we add some file
> to change the mode? Or having it hidden behing a module parameter
> and implement something better accessible if any need arrives?
The 'type' attribute is intended to reveal the GNSS receiver type
(class) as a hint to user space to avoid having to detect it at runtime
using heuristics.
It does not reflect which mode is currently active for receivers that
provide both a vendor specific protocol and NMEA (e.g. u-blox
receivers).
User space can currently switch modes at will by writing to /dev/gnss0
as Tony mentioned.
It may or may not make sense to make sure a particular mode is set
during probe, for example, if there's no real use for the proprietary
protocol and everyone would just switch away from it immediately.
Johan
Hi,
On Fri, 8 Dec 2023 08:39:21 -0600
Adam Ford <[email protected]> wrote:
> On Mon, Nov 27, 2023 at 2:51 PM Andreas Kemnade <[email protected]> wrote:
> >
> > Hi,
> >
> > On Mon, 27 Nov 2023 15:54:24 +0200
> > Tony Lindgren <[email protected]> wrote:
> >
> > [...]
> > > > - Output at /dev/gnssX:
> > > > AI2 vs. NMEA
> > > > The chip can be configured into sending AI2-encapsulated NMEA,
> > > > or proving data in a binary format.
> > > > Some research has to be done yet for the details.
> > > > A pile of logs is waiting for further analysis...
> > > >
> > > > Arguments for/against NMEA:
> > > > + Userspace is prepared to handle it
> > > > + Power management can be easily done by the kernel
> > > > - Less functionality can be used.
> > >
> > > I'd go with NMEA format as the default setting :)
> > >
> > yes, that would also be my preference.
> >
> > > > Arguments for/against AI2:
> > > > + Full functionality can be accessed from userspace (incl. A-GPS,
> > > > maybe raw satellite data)
> > > > - Userspace has to behave to have proper power management
> > > > - No freely (not even as in beer) tool available to fully use AI2,
> > > > so there will be only a real advantage after long "French Cafe"
> > > > sessions.
> > >
> > > Seems AI2 could be optionally enabled as needed with some writes
> > > to /dev/gnss0 to change the mode?
> >
> > Hmm, we have
> > /sys/class/gnss/gnss0/type to get the mode, maybe we add some file
> > to change the mode? Or having it hidden behing a module parameter
> > and implement something better accessible if any need arrives?
> >
> > If we want NMEA output, probably some init commands will be sent at
> > open(), but userspace doing something with AI2 probably does not want
> > the device touched, so it should probably be already be set before open().
>
> Is there another revision coming or should I try to test this one? I
> am not very familiar with the GNSS part of the module, but it sounds
> like there was some consensus as to which direction we should go. I
> should have a little time this weekend.
>
Progress is only in my test program. No more checksum errors, I have
made some progress in protocol reverse engineering. So make sure
you do a git pull for https://github.com/akemnade/bt200tools
Regards,
Andreas
On Fri, 8 Dec 2023 17:25:27 +0100
Johan Hovold <[email protected]> wrote:
> On Mon, Nov 27, 2023 at 09:51:08PM +0100, Andreas Kemnade wrote:
> > On Mon, 27 Nov 2023 15:54:24 +0200
> > Tony Lindgren <[email protected]> wrote:
>
> > > > - Output at /dev/gnssX:
> > > > AI2 vs. NMEA
> > > > The chip can be configured into sending AI2-encapsulated NMEA,
> > > > or proving data in a binary format.
> > > > Some research has to be done yet for the details.
> > > > A pile of logs is waiting for further analysis...
>
> Can you say something more about what the protocol looks like? Is there
> some common framing that can/should be stripped by the driver in both
> modes?
>
The frames (which can be fragmented into multiple gnss_recv_frame() calls)
consist of:
- some kind of start marker
- one or more tlv structures (start marker is escaped here)
- checksum
- end marker
In case of NMEA reporting we have with this patchset at /dev/gnssX or at /dev/tigps
found in the bt200 vendor kernel e.g.
1000 d3 1800 82050000 244750474c4c2c2c2c2c2c2c562c4e2a36340d0a 9f05 1003
which is:
1000 = start marker, d3 = NMEA report
1800 = length (LE)
82050000 = ms from turning on GPS (LE).
244750474c4c2c2c2c2c2c2c562c4e2a36340d0a = NMEA sentence
9f05 = checksum
1003 = end marker.
That is one report among others depending on what is enabled. So it
is not like the situtation with Sirf where you send some magic to turn
it into binary mode and some other magic turning it into NMEA mode
and have no other stuff on the line.
> > > >
> > > > Arguments for/against NMEA:
> > > > + Userspace is prepared to handle it
> > > > + Power management can be easily done by the kernel
> > > > - Less functionality can be used.
> > >
> > > I'd go with NMEA format as the default setting :)
> > >
> > yes, that would also be my preference.
> >
> > > > Arguments for/against AI2:
> > > > + Full functionality can be accessed from userspace (incl. A-GPS,
> > > > maybe raw satellite data)
> > > > - Userspace has to behave to have proper power management
> > > > - No freely (not even as in beer) tool available to fully use AI2,
> > > > so there will be only a real advantage after long "French Cafe"
> > > > sessions.
> > >
> > > Seems AI2 could be optionally enabled as needed with some writes
> > > to /dev/gnss0 to change the mode?
> >
> > Hmm, we have
> > /sys/class/gnss/gnss0/type to get the mode, maybe we add some file
> > to change the mode? Or having it hidden behing a module parameter
> > and implement something better accessible if any need arrives?
>
> The 'type' attribute is intended to reveal the GNSS receiver type
> (class) as a hint to user space to avoid having to detect it at runtime
> using heuristics.
>
> It does not reflect which mode is currently active for receivers that
> provide both a vendor specific protocol and NMEA (e.g. u-blox
> receivers).
>
> User space can currently switch modes at will by writing to /dev/gnss0
> as Tony mentioned.
>
Well, switching mode would in this case also mean configuring something
in the driver to do something different as it would mean sending commands
to enable NMEA reports and strip away the AI2 encapsulation in the driver.
You usually do not configure drivers through write() but through some
out-of-band means like ioctl(), sysfs, kernel compile options,
module parameters.
> It may or may not make sense to make sure a particular mode is set
> during probe, for example, if there's no real use for the proprietary
> protocol and everyone would just switch away from it immediately.
>
I would probably not do anything at probe time but turning on GPS and enable
NMEA reports at open() time.
With a lot of effort you can probably do interesting things with the
proprietary mode. But given the fact that apparently nobody has done
publicly so in the past years, I would not expect that anything arises
suddenly.
So in practice only NMEA would IMHO be useful and having raw AI2
might be something behind a module option or compile option to avoid
introducing some new API before a real need is seen.
Also as not everybody is using gpsd anymore, implementing any support
for AI2 in userspace would not be at a single place.
Regards,
Andreas