Re: Number of USB devices limited?

> Not specific to FreeBSD, but to the USB standard itself (I think). There is a limit to the number of endpoints, as you describe, but there is also a limit to the number of > hubs you can cascade. The number is low; I think it's 7. If you have more than $NUMBER of hubs in a row, you will get erratic behavior from your USB endpoints. And
> many things count as a "hub" - your computer probably takes up two, for example.

Thanks. I'll take a look when I get online and see if I can figure out what the hub[s] is[are]  adding to the overhead.

              -Brian
________________________________
From: Chris Hill <chris@monochrome.org>
Sent: Tuesday, April 19, 2022 11:09 PM
To: Brian McGovern (bmcgover) <bmcgover@cisco.com>
Cc: freebsd-questions@freebsd.org <freebsd-questions@freebsd.org>
Subject: Re: Number of USB devices limited?

Not specific to FreeBSD, but to the USB standard itself (I think). There
is a limit to the number of endpoints, as you describe, but there is
also a limit to the number of hubs you can cascade. The number is low; I
think it's 7. If you have more than $NUMBER of hubs in a row, you will
get erratic behavior from your USB endpoints. And many things count as a
"hub" - your computer probably takes up two, for example.


On Tue, 19 Apr 2022, Brian McGovern (bmcgover) wrote:

> Looking at the FreeBSD handbook, Chapter 13, it looks like the
> expectation is that I should be able to attach "the maximum of 126
> devices". Unfortunately, it seems I'm getting in the low 20s (21 FTDI
> serial cables, USB keyboard, and mouse), after which I start getting
> the following in the logs:
>
> "Error initializing deviceusb_alloc_device: device init 34 failed
> (USB_ERR_IOERROR, ignored)"
>
> and
>
> "uhub_reattach_port: could not allocate new device".
>
>
> If I look at /dev/ugen*, there are the ugen devices for 0.1->0.33; so
> its feeling like there may be limit in the serial port driver for the
> number of /dev/cua* devices, which presently only number
> cuaU0->cuaU20. So, I'm assuming this may not be a "USB" issue as much
> as the number of USB serial ports (ucom?) that can be connected.
>
> Before I go on a code crawl to figure out how this is failing and if
> it can be scaled up, I'm curious if anyone is aware of a coded limit
> for the number of USB serial devices (or USB devices in general) that
> can be connected before running in to this? I'm looking to push
> upwards to _maybe_ 40 FTDI devices.
>
>          -Brian
>

--
Chris Hill               chris@monochrome.org