USBSerial doesn't work with connect_blocking = false on STM32F401

[riaancillie]

Description of defect

The USBSerial device on mbed-os-6.10.0 and older (also tested previous version) does not seem to initialize the USB peripheral when the connect-blocking parameter is set to false in the constructor. When parameter is set to 'true', everything works as expected: code is paused until the microcontroller is connected to a host. Setting the parameter to 'false' the expectation is that code will continue to run as normal and that the microcontroller can be connected at a later stage to host, but this is not the case with the STM32F401: setting the parameter to 'false' results in no USB device being enumerated from the host - as if no pull-up is even being applied to D+.

Target(s) affected by this defect ?

Tested with Nucleo F401RE (C-02 revision)

Toolchain(s) (name and version) displaying this defect ?

Mbed Studio

What version of Mbed-os are you using (tag or sha) ?

mbed-os-6.10.0

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

Mbed Studio v1.4.1

How is this defect reproduced ?

VBUS connected to PA9, D- and D+ connected directly from USB connector to PA11, PA12 respectively.

Create a blank program in Mbed Studio and update the mbed-os library to mbed-os-6.10.0

mbed_app.json

{
    "requires": ["bare-metal","drivers-usb","events"],
    "target_overrides": {
        "*": {
          "target.c_lib": "small"          
        },
        "NUCLEO_F401RE": {                    
          "target.device_has_add": ["USBDEVICE"]          
        }
      }
}

main.cpp

#include <mbed.h>
#include <UsbSerial.h>

USBSerial usb(false); 

int main() {
  while(1) {
    ThisThread::sleep_for(500ms);    
  }
}

Further information

Drilling into USBSerial.h in the constructor implementation, adding connect() the else condition resolves the problem and allows the connection_blocking = false to work as expected (device connected to host at later time)

USBSerial::USBSerial(bool connect_blocking, uint16_t vendor_id, uint16_t product_id, uint16_t product_release):
    USBCDC(get_usb_phy(), vendor_id, product_id, product_release)
{
    _settings_changed_callback = 0;

    if (connect_blocking) {
        connect();
        wait_ready();
    } else {
        init();
        connect();  /// <---------------------------- I added this line and it seems to resolve the reported issue.
    }
}

[jeromecoutant]

Hi
Just a quick check.... does #14736 change your status ?
Thx

[riaancillie]

Hi
Just a quick check.... does #14736 change your status ?
Thx

Hi @jeromecoutant

I checked quickly. No, this did not resolve the issue. Also, please note that I switched to a different target sinced the last reported issue (F103 -> F401).

Methodology:
I cleaned the build folder and I added __HAL_PCD_ENABLE(&hpcd); as per #14736 and also some gargabe text. Compilation failed so I am sure that USBPhy_STM32.cpp is being compiled. I then removed the garbage text and tested again. USB device still not being detected.

I then attached a debugger. __HAL_PCD_ENABLE in USBPhyHw::init is definitely being hit.

Futher test that made a difference
As an experiment I added HAL_PCD_Start directly below __HAL_PCD_ENABLE and then the USB device is detected and working as expected. I verified with the debugger: Seems like USBPhyHw::connect() is never being called when connect_blocking = false and consequently HAL_PCD_Start is also not called.

Snippet of USBPhy_STM32.cpp

    HAL_StatusTypeDef ret = HAL_PCD_Init(&hpcd);
    MBED_ASSERT(ret == HAL_OK);

    __HAL_PCD_ENABLE(&hpcd);      //<!------ added as per #14736 - Does not fix issue on F401
    HAL_PCD_Start(&hpcd);    //<!------ I added this - This makes the USB device work as expected

    // Configure FIFOs
    #if (MBED_CONF_TARGET_USB_SPEED == USE_USB_NO_OTG)

[MubeenHCLite]

PR #14970