Why can't I integrate the CubeMX USB MSC code into the default end-node I-CUBE-LRWAN project?

[TW.16]

I want to add USB MSC functionality to my project which is based upon the I-CUBE-LRWAN project. My personal project is a stripped version of I-CUBE-LRWAN but the behaviour can be replicated by taking the I-CUBE-LRWAN end-node project and adding the generated USB MSC code to it.

I can get the merged code to work by doing a debug session and letting the MCU run with the debugger attached but if I run the code standalone nothing happens. This includes any other operations defined not just USB operations

An even more detailed question is found on stackoverflow

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I want to add USB MSC (Mass Storage Class, so USB storage drive) functionality to my Murata B-L072Z-LRWAN1 board. For this I have used the most recent I-CUBE-LRWAN end-node project and generated USB MSC code. I have done this in the past for older versions of the I-CUBE-LRWAN (a 2018 release) and gotten it working. However if I do it now I get two behaviours:

• Flash the board, connect it and then I reset the board. Nothing happens. No flashing lights, debug serial output, no USB and no LoRaWAN.
• Flash the board, connect it and then start a debugger session, I let it run freely without any breakpoints: full operation, lights work, debug serial works, USB presents itself and windows says it needs to format the drive. (Which is correct as the most barebones version does not have any storage interfacing added)

I can't explain this. Why does the code work when the debugger is attached but fully locks up when it is not? As for the changes between the older and newer versions of I-CUBE-LRWAN: they have changed from the systick to an RTC based timing setup. I however can't figure out how this is related to the debugger. 

Removing the USB Device cable does not make the code run. 

When I comment out the call to `MX_USB_DEVICE_Init`, windows sees an unidentifiable USB device but none of the code works (e.g. no debug UART output). When I uncomment `MX_USB_DEVICE_Init` nothing happens, no USB connect.

I'm using Keil uVision as my IDE. Compiler version: "default compiler version 6"

To replicate this you need a B-L072Z-LRWAN1 (modified to enable the USB pins) or that Murata chip with USB port. The full Minimal, Reproducible Example is to take the end-node project from [I-CUBE-LRWAN][1] and generating the USB MSC code in STM32CubeMX. (Target MCU is STM32L072CZTx). Then add all the USB MSC files to the end-node project and making the following additions to the project:

Add the USB_IRQHandler to `stm32l0xx_it.c`:

extern PCD_HandleTypeDef hpcd_USB_FS;
 
/**
 
* @brief This function handles USB event interrupt / USB wake-up interrupt through EXTI line 18.
 
*/
 
void USB_IRQHandler(void)
 
{
 
 HAL_PCD_IRQHandler(&hpcd_USB_FS);
 
}
 
```
 
Append the following clock configuration to `SystemClock_Config`:
 
```
 
RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};
 
 
 
while(!LL_RCC_HSI48_IsReady());
 
	
 
/*USB clock initialization	*/
 
PeriphClkInit.PeriphClockSelection |= RCC_PERIPHCLK_USB;
 
PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_HSI48;
 
if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
 
{
 
 Error_Handler();
 
}

And add the included `#include usb_device.h` and call to `MX_USB_DEVICE_Init();` in the `main.c`

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In relation to my old code, when I flash this to my board USB does work together with everything else (LEDs, LoRaWAN, debug UART).

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Running the USB MSC code on it's own works. Running the LoRaWAN code on it's own works. The problem only manifests in the merger of these two.

 [1]: https://www.st.com/en/embedded-software/i-cube-lrwan.html