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Need to use JTAG pin PA15 as Ext Interrupt in STM32F429

Question asked by panchal.jagdish on Aug 14, 2015
Kindly guide me to resolve this.
I have a board having STM32F429 on it. while adding new requirements in the board, a situation has arised such that i am left with no option other than to use port pin PA15 for External Interrupt. PA15 default function is for JTAG.

I tried following code to init port PA15 to use as External Interrupt but i observed that after running the code, Voltage level on port pin remain high (3.3V). 
I tested the circuit after disconnecting from the port pin, Found, that circuit works fine. It toggles between 3.3V and 0V, if the input to circuit toggles. 
But as i connect it to port pin, it remains high and does not toggle as expected.

The init code is as follows. Please guide me where i have done mistake.
void EXTILine15_Config(void)
  EXTI_InitTypeDef   EXTI_InitStructure;
  GPIO_InitTypeDef   GPIO_InitStructure;
  NVIC_InitTypeDef   NVIC_InitStructure;

  /* Enable GPIOA clock */
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
  /* Enable SYSCFG clock */
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE);
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_15;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  /* Connect EXTI Line15 to PA15 pin */
  SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOA, EXTI_PinSource15);

  /* Configure EXTI Line15 */
  EXTI_InitStructure.EXTI_Line = EXTI_Line15;
  EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
  EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising;  
  EXTI_InitStructure.EXTI_LineCmd = ENABLE;

  /* Enable and set EXTI Line15 Interrupt to the lowest priority */
  NVIC_InitStructure.NVIC_IRQChannel = EXTI15_10_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0F;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0F;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

I want port pin PA15 to work as External interrupt.