Pharo: read byte from Arduino serial port

Question

I have an Arduino hanging off /dev/ttyUSB1, communicating at 115kbaud. The statements below work fine up to the 's next' method call, where Pharo hangs. The Arduino responds to the '99' command by sending a single character $1 back to the computer. If I pull out the cable, the program continues and s contains the character $1 just like it should, but not until I pull out the cable. So it's my impression that 's next' does not return after it reads just a single byte (ok, sure, there's nothing that says it should return after reading a single byte). How do I read a single byte from a stream in Pharo? Or how do I open a read/write byte stream? I haven't found anything in the source classes that seem to do this. I've tried setting the stream to ascii, to binary, to text, and it doesn't change the behavior.

s := FileStream oldFileNamed: '/dev/ttyUSB1'.
s readWrite.
s nextPutAll: '99'. "'99' is successfully received by Arduino"
s next.             "hangs here"
s close.

Thanks for your help.

Answer 1

Take a look at the class side of FileStream. There you'll notice that you are getting a MultiByteStream (the concreteStream) when asking Filestream for an oldFileNamed:. There can be a TextConverter or buffer involved. open:forWrite: of MultiByteStream is called, and that calls super. StandardFileStream>open:forWrite: calls enableReadBuffering.

You probably want to call disableReadBuffering on your stream.

Answer 2

There is an Arduino package that has all these issues solved, take a look at this repo:

http://ss3.gemstone.com/ss/Arduino.html