HenryHunt HenryHunt - 1 month ago 14
Swift Question

ORSSerialPort data that should be a single line is coming in over multiple lines

I have an arduino that spits out a single line of GPS data down the serial line every half second, which I know works because I can look at the serial monitor in the arduino IDE and every half second, a new single line of data appears.

I'm now in the process of writing a Mac program using Swift that puts each coordinate on a map as it comes in through the serial port, and am using the ORSSerialPort library to connect to the arduino and receive its data. This works fine and I had a basic version working earlier, however I noticed that there were gaps in the GPS data (they were appearing in small groups on the map, with a noticeable space in between when it should be a constant line of them).

Before I had the map I had a text field that would have each GPS data line added to it as it came in, which produced the exact same output as the arduino IDE serial monitor, so I thought everything was working fine.

To try and fix the problem with the map I removed the map code and simply

print()
ed out each line into the XCode IDE as it came in through the serial port. To my surprise there were random line breaks in the data and I don't understand why. I feel that this may be causing the problems I am having (with splitting the string at every comma so I can extract the individual values) so would like to know why it comes out as a single line in the arduino IDE and the text field, but not in the XCode IDE and presumably whenever else I am working with the string.

EDIT: I prefixed the print to XCode IDE and the output to the text field with five plusses and suffixed them with five dashes, then set the serial port to close after sending a single report (what should be a single line of data). The output I got to both things ended up being three lines, each prefixed and suffixed with the plusses and dashes. See the photo below, which shows what should be a single line:



Why are my single lines of data coming through over multiple lines and behaving like individual variables (as in getting the last character of the line returns the last character of the first line of the three, not a semi colon)?

Answer

The issue isn't likely that there are extra newlines being inserted. Rather, ORSSerialPort (like the underlying POSIX API it uses) simply reports data to its delegate as it comes in. It has no way of knowing that for your particular use case you only want complete lines.

You need to buffer the incoming data and only process it when you've received a complete "line"/packet. ORSSerialPort includes an API, ORSSerialPacketDescriptor that makes this easier. There is further documentation for that API here: https://github.com/armadsen/ORSSerialPort/wiki/Packet-Parsing-API

Do note that this API doesn't (yet) support the use of a end delimiter only. You need to validate the entire packet beginning to end, as the parsing routine is "lazy". That is, it tries to find the smallest match possible starting from the end of the packet.