--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/device/timer.c	Fri May 26 23:11:05 2017 +0900
@@ -0,0 +1,77 @@
+// ARM dual-timer module support (SP804)
+#include "types.h"
+#include "param.h"
+#include "arm.h"
+#include "mmu.h"
+#include "defs.h"
+#include "memlayout.h"
+#include "spinlock.h"
+
+// A SP804 has two timers, we only use the first one, and as perodic timer
+
+// define registers (in units of 4-bytes)
+#define TIMER_LOAD	   0	// load register, for perodic timer
+#define TIMER_CURVAL   1	// current value of the counter
+#define TIMER_CONTROL  2	// control register
+#define TIMER_INTCLR   3	// clear (ack) the interrupt (any write clear it)
+#define TIMER_MIS      5	// masked interrupt status
+
+// control register bit definitions
+#define TIMER_ONESHOT  0x01	// wrap or one shot
+#define TIMER_32BIT    0x02 // 16-bit/32-bit counter
+#define TIMER_INTEN    0x20	// enable/disable interrupt
+#define TIMER_PERIODIC 0x40	// enable periodic mode
+#define TIMER_EN       0x80	// enable the timer
+
+void isr_timer (struct trapframe *tp, int irq_idx);
+
+struct spinlock tickslock;
+uint ticks;
+
+// acknowledge the timer, write any value to TIMER_INTCLR should do
+static void ack_timer ()
+{
+    volatile uint * timer0 = P2V(TIMER0);
+    timer0[TIMER_INTCLR] = 1;
+}
+
+// initialize the timer: perodical and interrupt based
+void timer_init(int hz)
+{
+    volatile uint * timer0 = P2V(TIMER0);
+
+    initlock(&tickslock, "time");
+
+    timer0[TIMER_LOAD] = CLK_HZ / hz;
+    timer0[TIMER_CONTROL] = TIMER_EN|TIMER_PERIODIC|TIMER_32BIT|TIMER_INTEN;
+
+    pic_enable (PIC_TIMER01, isr_timer);
+}
+
+// interrupt service routine for the timer
+void isr_timer (struct trapframe *tp, int irq_idx)
+{
+    acquire(&tickslock);
+    ticks++;
+    wakeup(&ticks);
+    release(&tickslock);
+    ack_timer();
+}
+
+// a short delay, use timer 1 as the source
+void micro_delay (int us)
+{
+    volatile uint * timer1 = P2V(TIMER1);
+
+    // load the initial value to timer1, and configure it to be freerun
+    timer1[TIMER_CONTROL] = TIMER_EN | TIMER_32BIT;
+    timer1[TIMER_LOAD] = us;
+
+    // the register will wrap to 0xFFFFFFFF after decrement to 0
+    while ((int)timer1[TIMER_CURVAL] > 0) {
+
+    }
+
+    // disable timer
+    timer1[TIMER_CONTROL] = 0;
+}