xx

1 files changed, 13 insertions, 11 deletions

diff --git a/trap.c b/trap.c
index 2b8fd41..9fe3c85 100644
--- a/trap.c
+++ b/trap.c
@@ -21,6 +21,19 @@ trapinit(void)
   // send interrupts and exceptions to kerneltrap().
   w_stvec((uint64)kerneltrap);
 
+  // set up the riscv Platform Level Interrupt Controller
+  // to send uart interrupts to hart 0 S-Mode.
+
+  // 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);
+
+  // set hart 0 S-mode priority threshold to 0.
+  *(uint*)0x0c201000 = 0;
+
   initlock(&tickslock, "time");
 }
 
@@ -43,17 +56,6 @@ 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){