The first 16 entries (through SysTick_Handler) are defined by the CortexM3 specification and the remainder are processor specific. The first entry in the table is not the address of an interrupt handler, but rather the address of the initial stack. At reset, the core loads the stack pointer from memory location 0x0000_0000 and begins execution at the the Reset_Handler location stored at memory location 0x0000_0004. This fragment also includes the entries for TIM3, USART1 and EXTI0, which we will be considering in this chapter