I have read in several places that when Dual Serial or Triple Serial USB mode is used, the SerialUSB (aka Serial) endpoint will be connected to the lowest-numbered of the assigned COM ports. Among other things, Visual Micro states this in their DBG documentation and suggests that debug should be assigned the highest of the SerialUSBx ports on the teensy side and the highest of the teensy COM ports on the PC side.
Unfortunately, this behavior is not what is observed. When Teensy Dual Serial USB is assigned two COM ports, Serial may appear on either the lower or the higher numbered port. The assignment persists through reconnections, but there are many scenarios in which Windows doesn't handle a disconnect rapidly enough, in which case the reconnect will cause two new COM port numbers to be assigned, and Serial could end up being either the lower or the higher COM number.
Similarly, in Triple Serial USB mode the Serial/SerialUSB port may end up on any of the three COM ports that are assigned (in my tests it most often appeared on the middle numbered port).
Here is an image showing SerialUSB1 on the lower numbered COM port and SerialUSB on the higher numbered Com port:
Here is an image showing the expected behavior: SerialUSB on the lower numbered COM port and SerialUSB1 on the higher numbered port:
Q1: does anybody know what determines the order in which SerialUSB endpoints will be assigned COM ports?
Q2: is there any way to cause Dual/Triple SerialUSBx COM ports to have descriptive names that distinguish them?
Q3: there are documented methods by which to determine the unique Teensy serial number associated with a connection. Do SerialUSB ports expose unique identifiers as well?
Unfortunately, this behavior is not what is observed. When Teensy Dual Serial USB is assigned two COM ports, Serial may appear on either the lower or the higher numbered port. The assignment persists through reconnections, but there are many scenarios in which Windows doesn't handle a disconnect rapidly enough, in which case the reconnect will cause two new COM port numbers to be assigned, and Serial could end up being either the lower or the higher COM number.
Similarly, in Triple Serial USB mode the Serial/SerialUSB port may end up on any of the three COM ports that are assigned (in my tests it most often appeared on the middle numbered port).
Here is an image showing SerialUSB1 on the lower numbered COM port and SerialUSB on the higher numbered Com port:
Here is an image showing the expected behavior: SerialUSB on the lower numbered COM port and SerialUSB1 on the higher numbered port:
Q1: does anybody know what determines the order in which SerialUSB endpoints will be assigned COM ports?
Q2: is there any way to cause Dual/Triple SerialUSBx COM ports to have descriptive names that distinguish them?
Q3: there are documented methods by which to determine the unique Teensy serial number associated with a connection. Do SerialUSB ports expose unique identifiers as well?