this post was submitted on 05 May 2024
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Keep in mind that it has been decades since I last used Kermit, but I'm pretty sure the use case it was originally designed for was...
Connect to a serial port, which had a modem attached. Talk to the modem and get it to dial a number. Presumably, the remote end answered and the port attached to its modem would issue a login prompt. Negotiate the login and then issue a bunch of commands to change directories and then launch Kermit on the remote system. After that Kermit to Kermit communications took over until you terminated the session. Finally, log off the remote system and hang up the modem.
All of this stuff could be done via scripts. I seem to remember that it would actually wait for a response, and then parse the response in the script. I don't remember ever doing polling loops.
If you're on a *nix box of some type, it's totally possible to open up a serial port for manual I/O even in something like a bash script. Even if you have to reverse telnet to a terminal server.
I started down the bash path but came unstuck when I wanted to create a process that uses a single bidirectional serial port to write a move command, whilst reading the current location and checking to see if an end stop switch was closed to write a stop command.
Ideally, all of it is interrupt driven, but I'm at a loss to see how I can do this with either Kermit or expect. Both appear to use a send, then wait for a response model, even if you can check for different responses.
Of note is that the end stop is external to the serial communication, so I can't check the same stream for that information.
Does this mean that you have some kind of other signals or pin-outs? If so, this is starting to sound like a great project for a Raspberry Pi, because the GPIO pin array can handle that.
Yeah, it's already on a pi, connected to my LAN and the USB port of the CNC. The switch is on a gpio pin.
I need to automate the calibration of the three axis. In other words, tell the CNC to move a specific distance, then figure out how far it actually moved, update the number of steps per mm, rinse and repeat.
To implement this, I have a known calibrated distance, a set of three 1-2-3 blocks, so I actually need to move until the switch closes, then ask the CNC how far it thinks it moved.
I intend to run this several times because right now, doing it manually is giving me weird results and I'm trying to figure out the root cause of the error.
So, I need to move an axis, interrupt the move if the switch is closed, and keep moving until the switch is closed.
Maybe then you need to move one stop up from scripting into something closer to actually programming. I'd be surprised if Python doesn't have the library support on a Pi for dealing with both serial and GPIO I/O.
Yeah, I was hoping to avoid that, but it's been heading that way for a few days now :}
I looked and Python has the library support for the GPIO and to do background threading to poll pins. My preference would be to go with a JVM language like Kotlin, but then I'm a programmer. Python, from the little that I've mucked about with it is really just one step in complexity from scripting. Maybe even easier, because some things in shell scripts are super difficult to do.