Re: Number of USB devices limited?

At the dayjob I will say that we’ve had good success using usb-to-8-port or usb-to-16 port devices that sidestep the issue of single discrete FTDI cables.

That said, if you have multiple boxes, the order in which they enumerate can sometimes be non-deterministic, based on which USB port the thing is plugged into, which probes first, and the phase of the moon.

-Dan

> On Apr 19, 2022, at 8:09 PM, Chris Hill <chris@monochrome.org> wrote:
> 
> 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