USB CDC and STOP2 power mode

[jstefan]

Posted on March 04, 2016 at 22:58

I am using a STM32L476 chip based on  CubeMX generated code .

I have ported this to a development board and implemented Stop2 power state to save battery life. I have a stop_x() and start_x() function for each device x that I use. They disable the device while in Stop2 mode and restore it for use on exiting Stop2.  I recently added USB CDC middleware to allow messaging with a PC. I have no real experience with USB and the middleware code. Currently, if I never enter Stop2 mode, the USB CDC functionality works. When I do use Stop2 mode, later, when we are running, the USB CDC will not ACK the initial Host message and fails to connect.  I do understand that, while connected to a USB host, that I should not enter Stop2 mode. There is really no need to conserve battery if powered by the USB.  I need to be able to continue using Stop2 after the host connection terminates.   How can I write stop_usb() and start_usb() functions that allow the USB to continue to work after we exit from Stop2 mode? I have tried:          1. Holding the USB in reset while in Stop2          2. Calling USBD_Stop() and USBD_Start()          3. Calling USBD_DeInit() and USBD_Init() None of the above methods has allowed the USB to survive the Stop2 state and connect with a host afterwards. Any ideas or examples would be appreciated. Thanks in advance, Jan      

[Walid FTITI_O]

Posted on March 10, 2016 at 17:59

Hi JanTM, 

Be sure that the exit from stop function is reconfiguring the System clock and it is providing the 48MHz to the USB peripheral.Otherwise, can you provide more details like the following:- What is the version of CubeMx that you have used ?- What is the operating system of the PC ?- The USB library that you are using ?- Did you have taked USB trace when entering /leaving stop mode?-Hannibal-