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Knowing when USB CDC is ready to tx

Question asked by Kent Swan on May 5, 2018

Context.  I using CubeMx on a STM32L462 with FreeRTOS (works fine).  When enabled, MX_USB_DEVICE_Init() is added to the default FreeRTOS task to activate a USB channel which also works fine.. I have my USB channel set up as a CDC serial io device (works fine) and have a VUSB bus detection on a GPIO EXTI input pin (also works fine but isn't hooked in). 

 

Case 1. If the application is sending via CDC_Transmit_FS the normal mechanism will busy out forever when the USB port disconnects which causes my queues to back up like a pluged up drain. This is bad.  I would normally expect some sort of a FAIL return in this case so that I could simply flush the output bytes rather than letting them pile up in the queues.

 

Question 1:  What is the normal HAL/CubeMx mechanism for the application to know that it is not connected to an active computer port.

 

Question 2: Given the ability to detect VUSB's presence, being plugged in or unplugged, what is the normal HAL/CubeMx mechanism to deinit and reinit the STM's USB device subject to the answer to Question 1.

 

Any pointers will be helpful.

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