Re: [gpsd-dev] Modifying (severly) hardware.html

[Gary E. Miller]

Yo Hal!

On Wed, 15 Apr 2015 02:51:16 -0700
Hal Murray <address@hidden> wrote:

> 
> address@hidden said:
> > (The Sure board uses an engine called a SKG16B which is otherwise
> > unattested. The Adafruit hat has a Venus 6 in it.) 
> 
> Adafruit has several GPS gizmos.
> 
> One is a HAT for Raspberry Pi.
>   http://www.adafruit.com/products/2324
> 
> Another is a breakout board.
>   https://www.adafruit.com/products/746
> 
> They both use the same module which includes an antenna and a MTK3339
> chip.  Their web page for the HAT doesn't mention the MTK3339.

Yeah, it does, way down near the end of many pages there is an image
of the schematic, which shows the MTK3339.  They glue the antenna
over the chip, so visual inspection can not confirm.

https://learn.adafruit.com/adafruit-ultimate-gps-hat-for-raspberry-pi/downloads

It identifies to gpsctl as an MTK-3301:

address@hidden:/usr/local/src/GPS/gpsd/gpsd# gpsctl /dev/ttyAMA0
/dev/ttyAMA0 identified as a MTK-3301 AXN_2.31_3339_13101700-5632 at 9600 baud.



> Is that enough to figure out how to support the 3339?

What is not supported?  Works great for me.  Except this seems to do nothing:

# gpsctl -b /dev/ttyAMA0

>  If not, is
> there something simple I can type to get more info or would it be a
> lot easier if you had access to it?  I think the data sheet is on the
> breakout board web page.

I can also give ssh access to my RasPi2 if anyone wants to look.

> Another thing we need is a list of USB chips that do/don't support
> PPS.  How does that very with OS?

AFAIK, all GNSS chips support PPS, and all USB<->Serial converter chips
can support it.  The vendors choose not to.  Some claim so as not to 
confuse newbies.

> There is another worm is this can.  Is there a difference between
> supported (meaning gpsd uses the proprietary binary protocol) and
> works well in NMEA mode?

Huge difference.  A few binary mmodes are good, some really suck (Garmin).

"Supported Well" usually means good PVT performance.  How/If a unit
supportd 50bps data, raw measurements, etc., is all over the map.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588