Date: Tue, 19 Apr 2022 23:09:06 -0400 (EDT) From: Chris Hill <chris@monochrome.org> To: "Brian McGovern (bmcgover)" <bmcgover@cisco.com> Cc: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org> Subject: Re: Number of USB devices limited? Message-ID: <alpine.BSF.2.20.2204192304410.2458@tripel.monochrome.org> In-Reply-To: <BL1PR11MB550957CB5932655D66799676C5F29@BL1PR11MB5509.namprd11.prod.outlook.com> References: <BL1PR11MB550957CB5932655D66799676C5F29@BL1PR11MB5509.namprd11.prod.outlook.com>
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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
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