CDC callbacks on disconnection/reconnection

[moritzstoetter]

We are running TinyUSB v0.18.0 on a STM32H7 in CDC device mode, and are experiencing difficulties around the detection of physical disconnection/reconnection.

What we observe:

• When a serial port is opened, then tud_cdc_line_state_cb gets called with dtr and rts set to true.
• When a serial port is closed, then tud_cdc_line_state_cb gets called with dtr and rts set to false.
• With the serial port opened: When the cable is disconnected, then tud_suspend_cb gets called (not tud_cdc_line_state_cb or tud_unmount_cb).
• With the serial port opened: When the cable gets reconnected, then tud_mount_cb gets called (not tud_cdc_line_state_cb or tud_suspend_cb).

Our internal state machine relies on knowledge about the cdc port's state, and with this limitation we are having great difficulty to get things working smoothly.

Questions:

• Is this a bug or is this intended behavior?
• What is the intended way to handle physical dis-/reconnection? Are there any reasonable workarounds?
• Might this be related to tud_cdc_connected() or tud_cdc_line_state_cb() problem when unplug USB connector #1187?