Need help with reading from serial port

[Jörg Krause]

Hi,

I am trying to read data from a serial port using Luvit. My simple example is running, however, I have an issue with fs_read() as it calls the callback function even if no data are received.

This is my example: https://gist.github.com/joerg-krause/cba5a56577a0483ceb8ea4ecda5ff0ba

This is the output:

# luvit main.lua 

''

''

''

''

''

My problem with this issue is that it consumes much more CPU cycles on my embedded Linux system than reading from "/dev/input/event0".

Any ideas what's wrong here?

[Tim Caswell]

I don't have any idea what's wrong, but several of us have been trying to get serial support (or at least the ability) into upstream libuv, you can see much of the history at https://github.com/libuv/libuv/pull/484

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[Jörg Krause]

Many thanks for the link! I think fs_read() does not work for Linux serial ports as underlying read() system call reads EOF from the serial interface.

If I try to use a Luvits ReadStream interface, the 'end' callback is called before I receive any data.

So, lets hope there will be support for serial ports in libuv soon.

[Tim Caswell]

You can maybe try to use the pipe interface as it accepts arbitrary file descriptors.  That's what I use to create pty's in luvit.

https://luvit.io/blog/pty-ffi.html

[Vladimir Dronnikov]

tty is likely set in non-blocking mode -- that may lead to EOF storm.

[Jörg Krause]

Not sure why my last post was deleted.

I'm back from vacation and I will have a closer look at your example soon. Many thanks!

[Martin Croome]

Hi Jorg

We have working serial support, The tack we took is a mixture of Luvit, C and FFI. We use FFI for read and write, C for line monitoring threads and Luvit (uv.poll for events on the port).

Regards

Martin

[Tim Caswell]

Are there any small simply primitives that I could bake into luvi that made this possible with pure lua+ffi?  I know I would use serial all the time if I had the option (for talking to microcontrollers over USB mostly)

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[Jörg Krause]

I finally used ffi with libserialport for doing all the serial configuration and reading from the port: https://gist.github.com/joerg-krause/6d0a8a4949670ee103e6c22006f0cc37.

I guess it is not very luvit idiomatic, but at least it works for me.

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