我使用的芯片是 MK16Z64VHL4,在数据手册中描述关于中断有如下

3.3.2.3 Interrupt channel assignments
The interrupt vector assignments are defined in the following table.
• Vector number — the value stored on the stack when an interrupt is serviced.
• IRQ number — non-core interrupt source count, which is the vector number minus
16.

配置中断时是用IRQ num

比如：SYStick中断，就是 enable_irq(-1);

可能对NVIC等概念我不是很清楚，所以请大家帮我解释一下，这两个概念有什么不同？