When I used the serial port in windows I had to flush to send. I also used the input/output file not two separate ones. <div class="gmail_quote">On Mar 13, 2012 1:28 PM, "Matthew Flatt" <<a href="mailto:mflatt@cs.utah.edu">mflatt@cs.utah.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> At Tue, 13 Mar 2012 17:20:12 +0100, Rüdiger Asche wrote: > Thanks, that sort of works, but only sort of... here is the portmon > trace - it turns out that the open won't quite work, and nothing is > output until the port is being closed - looks like some setup of the > port is missing (eg setting output buffer size). Just to make sure, you're either explicitly setting the output port to unbuffered or using `flush-output', and it still doesn't flush? Unfortunately, I don't know about setting COM1 parameters. Maybe you can use the `mode' shell command via `system'? Our use the FFI to call functions like SetupComm()? ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </blockquote></div>