Consider an embedded machine controller:
A USB input port on the controller ties to a TUSB2046B 4 port hub, fed by an Intel NUC small form factor computer running Windows 10.
Three of the four downstream ports on the embedded hub are connected directly to FTDI FT232RL USB-to-serial converters.
The remaining port is stubbed off to a front panel connector, appropriately terminated and so on. All of this is working fine.
The three serial converters are connected to three Atmel XMega microcontrollers running various parts of the machine. For ease of field updates, the design uses the Arduino-style boot loader configuration. The Arduino develoment environment uses the DTR line as a means of injecting a reset signal to restart the processor, to allow the environment to upload new application code to the processor. All of this works fine too.
What doesn't work fine is insertion of some other USB device into the system. If a thumb drive (for example) is plugged into the NUC, all four of the USB ports undergo a reset/restart cycle, which causes a momentary drop of DTR. This resets each of the processors too. That's not a good thing when those processors are in the middle of running a motion stage and a microscope. The same thing happens when any other USB device is disconnected as well. It happens whether the connect/disconnect happened on an external hub or a port directly on the NUC chassis.
Is there a way to prevent this reset/restart/whatever from happening when some other device is plugged into a USB port on the NUC? This machine exposes two USB ports to the user, for external installation of a bar code reader, thumb drive or external hard disk. If a user walks up and plugs in a thumb drive, we do NOT want the machine to fall over dead....but that's what it's doing right now. Worst case, I can eliminate the DTR-based reset circuit and force updates to be implemented only by opening the machine up and plugging in a programmer, but that makes field updates a big problem.
What I want is for the USB connection to remain stable regardless of what other devices may be plugged in or removed while the machine is operating. I don't know if this behavior is an inherent part of how USB works at the OS/BIOS level, or if it's something that's related to plug-and-play, or if it's something related to a registry setting, or something implemented at the driver level, or ???? (Help!)
MGF
