TM4C129X Evaluation Board and boot-demo-usb not working. Why?

Hi Amit,
finally I managed to make it work!

I started from this article in the wiki, found searching on the support forum. So I had the suspect that device was not properly turning on in device mode. I modified the source code of boot-demo-usb adding the following line

    //
    // Set the USB stack mode to Device mode with VBUS monitoring.
    //
    USBStackModeSet(0, eUSBModeForceDevice, 0);

just before USBDHIDMouseCompositeInit call, and suddenly boot-demo-usb started to work.

Then I did the same test on usb_dev_serial demo. The plain code was not running on my demo board, no USB interrupt arrived. So I opened usb_dev_serial.c and changed the following line

    //
    // Set the USB stack mode to Device mode with VBUS monitoring.
    //
    USBStackModeSet(0, eUSBModeDevice, 0);

into this one

    //
    // Set the USB stack mode to Device mode with VBUS monitoring.
    //
    USBStackModeSet(0, eUSBModeForceDevice, 0);

and also usb_dev_serial demo started working.

And so came my bootloader turn to work. As it's not using usblib, I couldn't call USBStackModeSet directly. I had to dig into usblib to find that the magic is done by writing the correct bit into USB's GPCS register (that is not documented in TM4C129KCPDT datasheet as it's marked as under NDA). Basically I modified the USBBLInit found in bl_usbfuncs.c in this way:

void
USBBLInit(void)
{
    bool bForceDevice = true; //<<<<<<<<<<<<<< ADDED CODE
	
    //
    // Configure the USB Pins based on the bl_config.h settings.
    //
#if defined(USB_VBUS_CONFIG) || defined(USB_ID_CONFIG) || \
    defined(USB_DP_CONFIG) || defined(USB_DM_CONFIG)
    USBConfigurePins();
    bForceDevice = false; //<<<<<<<<<<<<<< ADDED CODE
#endif

    //
    // Initialize a couple of fields in the device state structure.
    //
    g_sUSBDeviceState.ui32Configuration = DEFAULT_CONFIG_ID;

    //
    // Enable the USB controller.
    //
    HWREG(SYSCTL_RCGCUSB) = SYSCTL_RCGCUSB_R0;

    //
    // Wait for the peripheral ready
    //
    while((HWREG(SYSCTL_PRUSB) & SYSCTL_PRUSB_R0) != SYSCTL_PRUSB_R0)
    {
    }

#if defined(TARGET_IS_TM4C129_RA0) ||                                         \
    defined(TARGET_IS_TM4C129_RA1) ||                                         \
    defined(TARGET_IS_TM4C129_RA2)
    //
    // Turn on USB Phy clock from PLL VCO
    //
    HWREG(USB0_BASE + USB_O_CC) = (USB_CC_CLKEN | (7 << USB_CC_CLKDIV_S));
#else
    //
    // Turn on USB Phy clock.
    //
    HWREG(SYSCTL_RCC2) &= ~SYSCTL_RCC2_USBPWRDN;
#endif

    //
    // Clear any pending interrupts.
    //
    HWREGH(USB0_BASE + USB_O_TXIS);
    HWREGB(USB0_BASE + USB_O_IS);
		
    //
    // Check if USB must be forced in device mode as there is no hardware way to do so
    //
    if (bForceDevice)                                          //<<<<<<<<<<<<<< ADDED CODE
    {                                                          //<<<<<<<<<<<<<< ADDED CODE
        HWREGH(USB0_BASE + USB_O_GPCS) |= USB_GPCS_DEVMOD;     //<<<<<<<<<<<<<< ADDED CODE
    }                                                          //<<<<<<<<<<<<<< ADDED CODE

    //
    // Enable USB Interrupts.
    //
    HWREGH(USB0_BASE + USB_O_TXIE) = USB_TXIS_EP0;
    HWREGB(USB0_BASE + USB_O_IE) = (USB_IS_DISCON | USB_IS_RESET);

    //
    // Default to the state where remote wakeup is disabled.
    //
    g_sUSBDeviceState.ui8Status = 0;
    g_sUSBDeviceState.bRemoteWakeup = false;

    //
    // Determine the self- or bus-powered state based on bl_config.h setting.
    //
#if USB_BUS_POWERED
    g_sUSBDeviceState.ui8Status &= ~USB_STATUS_SELF_PWR;
#else
    g_sUSBDeviceState.ui8Status |= USB_STATUS_SELF_PWR;
#endif

    //
    // Attach the device using the soft connect.
    //
    HWREGB(USB0_BASE + USB_O_POWER) |= USB_POWER_SOFTCONN;

    //
    // Enable the USB interrupt.
    //
    HWREG(NVIC_EN1) = 1 << (INT_USB0 - 48);
}

And that did the trick.

My final thoughts:

1. As nobody seems to have found the same problem on the evaluation board, I should have a faulty board or a faulty uC on board, on which VUSB is not correctly detected the way that device mode, if not forced, does never start to work
2. I tried to pull out all of the J25 jumpers from evaluation board, and board is still detected with the modified demo code, so it' true that device mode is really forced
3. ROM bootloader seems to use only DP/DM pins, as it works both on the evaluation board, without J25 jumpers inserted,  and on my board, which uses only DP/DM, so it has to force device mode for sure

Thanks for your support and regards,
Stefano