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Re: [gpsd-users] Sending SiRF commands to GPS receiver

From: Eric S. Raymond
Subject: Re: [gpsd-users] Sending SiRF commands to GPS receiver
Date: Sun, 26 Feb 2012 01:17:31 -0500
User-agent: Mutt/1.5.21 (2010-09-15)

Alexander Carver <address@hidden>:
> Is it possible to send any SiRF command to a GPS via gpsd or can you
> only send certain commands already in the source code?  I see the -x
> in gpsctl but it's not clear how to send SiRF messages (SiRF isn't
> one of the listed examples).

It's not possible to send general control messages from an ordinary 
gpsd client.  It is possible to do it via the gpsctl utility; you should
look into that.  

The reason for this restriction is that the devices gosd manages are shared
resources.  The capability to send unrestricyed control messages from a
client could be a tool with which to DOS other users.
> I specifically want to send message 133 (0x85) which toggles the
> DGPS source of the receiver.  I've discovered that my receiver
> occasionally loses the SBAS satellite and won't recover it on its
> own.  However, toggling the source from SBAS to NONE and then back
> to SBAS causes it to lock onto the satellite again.
> The message is seven bytes long:
> MsgID (1 byte unsigned), Source (1 byte unsigned), internal beacon
> frequency (4 bytes unsigned), internal beacon bitrate (1 byte
> unsigned)
> The last two are unused when selecting SBAS and are set to zero so
> turning off DGPS should use this message payload (hex spaced out to
> show message divisions):
> 85 00 00000000 00
> And turning it back on set to SBAS is:
> 85 01 00000000 00

Which SiRF is this?  I could make this sequence part of the configuration
string set at device wakeup time; that way, if the device had lost the 
satellite during a session, it would be re-acquired whenever the device
is reopened by another WATCH.
                <a href="";>Eric S. Raymond</a>

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