GPIO PIN interrupt IST flag is not setting in LPC 1837

Hi, I am trying to enable GPIO PIN interrupts using following procedure, But not getting why flags in IST itself not setting. Please anyone point what went wrong here my code: NVIC_DisableIRQ...
GPIO PIN interrupt IST flag is not setting in LPC 1837

Hi, I am trying to enable GPIO PIN interrupts using following procedure, But not getting why flags in IST itself not setting. Please anyone point what went wrong here my code: NVIC_DisableIRQ...