1 files changed, 13 insertions, 0 deletions
diff --git a/trap.c b/trap.c
index 74f3456..2b8fd41 100644
--- a/trap.c
+++ b/trap.c
@@ -42,6 +42,19 @@ usertrap(void)
   
   // save user program counter.
   p->tf->epc = r_sepc();
+
+  // PLIC setup
+  // qemu makes UART0 be interrupt number 10.
+  int irq = 10;
+  // set uart's priority to be non-zero (otherwise disabled).
+  *(uint*)(0x0c000000L + irq*4) = 1;
+  // set uart's enable bit for hart 0 s-mode. 
+  *(uint*)0x0c002080 = (1 << irq);
+
+  // hart 0 S-mode priority threshold.
+  *(uint*)0x0c201000 = 0;
+
+  intr_on();
   
   if(r_scause() == 8){
     // system call