Re: [gpsd-dev] ✘Change FIXED_PORT_SPEED and FIXED_STOP_BITS

[Gary E. Miller]

Yo Hal!

On Tue, 29 Oct 2019 13:41:22 -0700
Hal Murray <address@hidden> wrote:

> address@hidden said:
> > The big problem is that POSIX has no way to notify a program that
> > it is seeing parity errors and overruns.   
> 
> > Any thing I think of to work around this is ugly and/or
> > non-portable.   
> 
> If the system that gpsd is running on silently discards characters
> with wrong parity, one possibility if you know what to expect is to
> look for the mangled pattern that is what-you-expect without the
> characters that have bad parity.

The problem is deeper than that.  When gpsd is set to 8N1, it will
accept chars sent at 8O1 just fine.  They pass all checksum tests, etc.

BUT, when gpsd then sends data to the receiver at 8N1, when it
is expecting 8O1, the receiver rejects the commands.  This is
indistringuishable from a disconnect TX line to the receiver, or a
receiver that does not understand what is being sent due to version
incompatibilities.

This is a big problem with the TSIP which does not bother to ACK
or NACK most commands sent to it.

Even if that were not so, gpsd must first identify the type of receiver
in order to determine the type of messages in order to know what
chacksums to apply.  Chicken and egg problem.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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