如何在Rust中更改cortex-m4处理器上的异常优先级？

[dependencies]
cortex-m = "0.7.3"
cortex-m-rt = "0.7.3"

#![no_main]
#![no_std]

use cortex_m::asm;
use cortex_m_rt::entry;

#[entry]
fn main() -> ! {
    // 设置异常向量表
    unsafe { cortex_m::interrupt::disable() };
    cortex_m::interrupt::free(|_| {
        let scb = cortex_m::peripheral::SCB::ptr();
        scb.vtor.write(0x08004000); // 向量表的起始地址
    });

    // 启用异常
    unsafe { cortex_m::interrupt::enable() };

    loop {
        // 程序主循环
    }
}

use cortex_m::peripheral::NVIC;

// 设置SysTick异常的优先级为2
unsafe { NVIC::unmask(Interrupt::SysTick) };
cortex_m::peripheral::NVIC::set_priority(Interrupt::SysTick, 2);