Implementing tight time constraints for read/write with USB serial (ftdi_sio)

[Thomas Bracht Laumann Jespersen]

On Tue, 4 Sep 2018 at 07:31, Greg KH <greg at kroah.com> wrote:
>
> On Mon, Sep 03, 2018 at 09:12:35PM +0200, Thomas Bracht Laumann Jespersen wrote:
> > Hello all!
> >
> > I'm working on a project where we want to integrate into a production line and
> > listen on connected devices, and the challenge is that our setup needs to be
> > fast enough.
>
> First off, "tight time constraints" and "usb-serial" should never be in
> the same sentence, unless you use the words "never will happen" in there
> as well :)

I'm learning (beginning to accept) that :-) This is pretty new territory for me,
so I appreciate the wisdom.

>
> There are loads of issues with trying to use USB with anything you wish
> to have low-latency or determinism with, and then throw a usb-serial
> device into the mix and all bets are off.  Remember there is a little
> microcontroller out there at the end of the usb-serial device running a
> UART and some unknown firmware blob that can take its time and do
> anything it wants at any point in time, which can, and will, cause you
> all sorts of headaches as you are finding out.
>
> If you _really_ need to do something like this, use a UART attached to a
> PCI card, you will have much better control and be able to actually do
> what you are wanting to do here.

We need to find a solution somehow, so thanks for the suggestion. I'll keep
digging for solutions, but if you have any good resources I should look at, I'm
all ears.

>
> Good luck!

Thank you!