diff --git a/plic.c b/plic.c
new file mode 100644
index 0000000..0f19ab0
--- /dev/null
+++ b/plic.c
@@ -0,0 +1,63 @@
+#include "types.h"
+#include "param.h"
+#include "memlayout.h"
+#include "riscv.h"
+#include "defs.h"
+
+//
+// the riscv Platform Level Interrupt Controller (PLIC).
+//
+
+void
+plicinit(void)
+{
+  // set uart's priority to be non-zero (otherwise disabled).
+  *(uint32*)(PLIC + UART0_IRQ*4) = 1;
+}
+
+void
+plicinithart(void)
+{
+  int hart = cpuid();
+  
+  // set uart's enable bit for this hart's S-mode. 
+  //*(uint32*)(PLIC + 0x2080)= (1 << UART0_IRQ);
+  *(uint32*)PLIC_SENABLE(hart)= (1 << UART0_IRQ);
+
+  // set this hart's S-mode priority threshold to 0.
+  //*(uint32*)(PLIC + 0x201000) = 0;
+  *(uint32*)PLIC_SPRIORITY(hart) = 0;
+}
+
+// return a bitmap of which IRQs are waiting
+// to be served.
+uint64
+plic_pending(void)
+{
+  uint64 mask;
+
+  //mask = *(uint32*)(PLIC + 0x1000);
+  //mask |= (uint64)*(uint32*)(PLIC + 0x1004) << 32;
+  mask = *(uint64*)PLIC_PENDING;
+
+  return mask;
+}
+
+// ask the PLIC what interrupt we should serve.
+int
+plic_claim(void)
+{
+  int hart = cpuid();
+  //int irq = *(uint32*)(PLIC + 0x201004);
+  int irq = *(uint32*)PLIC_SCLAIM(hart);
+  return irq;
+}
+
+// tell the PLIC we've served this IRQ.
+void
+plic_complete(int irq)
+{
+  int hart = cpuid();
+  //*(uint32*)(PLIC + 0x201004) = irq;
+  *(uint32*)PLIC_SCLAIM(hart) = irq;
+}