Number of USB devices limited?

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