[time-nuts] GPScon running on Raspberry Pi 3b

[Mark Sims]

Heather only requires TXD, RXD, and GND.   If you want to use the temperature control feature RTS and DTR.

Most Linux distros have decent USB serial port drivers built in.  I tend to use no-name Chinese PL-2303 based USB dongles... because I have them.   They have worked fine on all the Linuxy stuff I have used and the Windows drivers they shipped with work.

I no longer use FTDI based devices since there are LOTS of clone chips out there and FTDI is rather aggressive about having their (Windows) drivers not work with them.  Since there is no way to tell what chip is actually being used in a dongle, I just avoid the FTDI stuff and any potential hassles.  There are also fake Prolific chips out there and Prolific has also been known to block their Windows drivers from working with them.  If you can find genuine FTDI / Prolific chip based dongles, they are great... but buyer beware these days.

I also have some CH3xx dongles that have some clone chips in them.  Many Linux drivers don't seem to be able to set the baud rate on those.

Something recently changed on one of my Win XP boxes (perhaps installing the TL-833 prom burner software) and some of my PL-2303 dongles have started acting up.  After a day or two of continuous operation they start randomly dropping received bytes.  No issues running the same dongles on PI / Linux / macOS or previously on that XP system.  

The garbaged received data did help my find a bug in Heather...  they could produce numbers like 1.2345E300.   Heather was expecting a number like 9.8765 and tried to format and print the value.  The resulting 300 character string overflowed a buffer and crashed the program.   Now my number reader routines do a sanity check and reject obviously bogus values, NANs, INFs, etc.

The PI does have a couple of logic level serial ports on the expansion connector you can connect a level shifter two.  One port is normally the Linux serial console which you can configure to be a general purpose serial port (I've never used them, but others have).

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> Are there any special requirements for using a USB to RS-232 adapter on the
Pi? Any specific features for the RS-232 adapter to get all of the features
for Lady Heather?