Instek oscilloscope, RXTX, USB serial woes

Lost a day to trying to debug the serial receive logic in the Linux kernel. Hadn't tried that before, but have to say that inserting

printk(KERN_DEBUG "Handy debug message here\n");

throughout the serial and tty code was an easier than expected experience. I'd read people saying that before, but didn't really believe them. You really can just edit the kernel source, insert your debugging code (caveat haxor!) rebuild, reboot, and see what goes on in a live kernel by looking in /var/log/debug. After doing a lot of debug message inserting, rebooting my PC and that pesky oscilloscope many, many times and reading a lot of debug messages, I reckon I don't know what the problem is. I'm fairly certain that the problem is not with the PC, but with the oscilloscope.

Freewave and Portmon

Freewave, the software that can be used with the scope, mysteriously started working again. The meaningless dialog box (that meant the software tried to do something that it shouldn't) has gone away, so I tried fetching a large sample set from the scope again. This time, I downloaded Portmon from Microsoft. I wish I'd done this at the start. Oh yeah, I remember, this all started when Freewave mysteriously stopped. Anyway, Portmon tells me that the Freewave software doesn't just send a series of commands to the scope, it seems to reset the serial port after each command, and follow it up with two 'purge's. To be sure to be sure, obviously. In fact, there are three purges after each command. I'm not sure what effect these will have on the scope - after all, only rx, tx and gnd are connected at the port. The RXTX package stays fairly faithful to the Java Stream definitions, so I'll try some close()-open()s and a flush or two. If it all goes a bit stable, I'll post the code and a picture or two,

ttyACM0

Something that caught me out badly a few times was ttyACM0, the device file for the scope's USB connection, being created with 660 permissions, owned by root.root. I edited my udev.rules file, found under /etc/udev, to fix this issue. I'd be more explicit about it, but I'm not convinced I did it perfectly! I must read up about udev one day.

Better get this code tidied up, post a final message, and get back to some proper work!