How to trap in external interrupt while there is a keystroke

[LoveZJT]

In my bare-mental examples, I want to trap into external interrupt while there is a keystroke.

I read the riscv-privileged-v1.10 and SiFive U54 Core Complex Manual to learn external interrupt and PLIC. I think that only after initialing PLIC can it trap into external interrupt if there is a keystroke.

So I init PLIC as follow.

// Pseudocode

//set MIE of mstatus
asm volatile ("li t0, 0x8; csrw mstatus, t0");

// set MEIE bit of MIE
asm volatile ("li t0, 0x800; csrw mie, t0");

// set the priority of all interrupt sources to 1
plic_priority = PLIC_PRIORITY_BASE_ADDR;
for(int i=0;  i<127; ++i)
     plic_priority[i] = 1;

// enable all interrupt sources
plic_enable = PLIC_ENABLE_BASE_ADDR;
for(int i=0; i<127; ++i)
     plic_enable[i] = 1;

// permit all interrupt sources
plic_threshold = PLIC_THRESHOLD_BASE_ADDR;
*plic_threshold = 0;

But I fail to trap into external interrupt while knocking on the keyboard. Do I miss something or I got this completely wrong? Thx