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STM32F072 USART becomes unresponsive after jump from custom bootloader to application code

Question asked by Yadav.Ajay on Oct 17, 2016
Latest reply on Oct 18, 2016 by Clive One
Hi, I wrote a custom bootloader which downloads new firmware using GSM module and starts application firmware. Bootloader is able to start application firmware and application firmware is able to configure vector table, systick and different I/O pins. But is unable to communicate on any USART interface. 
Below is code to jump to application firmware from bootloader:

// Jump to user application
JumpAddress = *(__IO uint32_t*) (ApplicationAddress + 4);
Jump_To_Application = (pFunction) JumpAddress;
// Initialize user application's Stack Pointer
__set_MSP(*(__IO uint32_t*) ApplicationAddress);

Below is start of main() in application firmware:
void Remap_Table(void)
    // Copy interrupt vector table to the RAM.
    volatile uint32_t *VectorTable = (volatile uint32_t *)0x20000000;
    uint32_t ui32_VectorIndex = 0;
    for(ui32_VectorIndex = 0; ui32_VectorIndex < 48; ui32_VectorIndex++)
        VectorTable[ui32_VectorIndex] = *(__IO uint32_t*)((uint32_t)FIRMWARE_START_ADDR + (ui32_VectorIndex << 2));
   RCC_APB2PeriphResetCmd(RCC_APB2Periph_SYSCFG, ENABLE);
    // Remap RAM into 0x0000 0000
int main(void)
    SysTick_Config(SystemCoreClock / 1000);
    //NVIC_SetPriority(SysTick_IRQn, 0x0);
    configureImu();      //configures I2C Interface
    configureDebugger();   //configures USART4
    configureLidar();    //configure I2C
    configureGps();  //configure USART3

Device is able to configure interfaces but when trying to access USART to write data it keeps on looping at :
while (USART_GetFlagStatus(USART3, USART_FLAG_TXE) == RESET);

Transmit Data Register of USART is not getting set.

Can anyone please tell me what I am missing or doing wrong?