// 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;
}