ps1bsp/time.c

#include "common.h"
#include "time.h"

#include <hwregs_c.h>

static volatile u_long realTime;    // Real time in 20,12 format (4096 ticks per second)
static u_long frameNumber;          // Number of game ticks
static u_long frameStartTime;       // Real time at which the current frame began
static u_short frameDeltaTime;      // Real time since last game tick in 4,12 format

static u_short avgFrameRate;        // Average framerate over the last 16 frames in 8,8 format
static u_long measureStartTime;

static void timer_callback()
{
    realTime += 16;
}

void time_init()
{
    realTime = 0;
    frameNumber = 0;
    frameStartTime = 0;
    frameDeltaTime = 1; // Prevent division by zero for any code using this number on the first frame
    
    avgFrameRate = 0;
    measureStartTime = 0;

    // Set the timer such that we get exactly 256 interrupts per second on both PAL and NTSC (roughly once per 4 milliseconds)
    // This allows the game speed to be completely framerate and video mode independent
    const int counter = 16384;

    EnterCriticalSection();
	SetRCnt(RCntCNT2, counter, RCntMdINTR);
	TIMER_CTRL(2) = 0x1E58;
	InterruptCallback(6, timer_callback);
	StartRCnt(RCntCNT2);
	ChangeClearRCnt(2, 0);
	ExitCriticalSection();
}

void time_tick()
{
    ++frameNumber;

    u_long currTime = realTime;
    if ((frameNumber & 0xF) == 0)
    {
        u_long timeDelta = currTime - measureStartTime;
        if (timeDelta == 0)
            timeDelta = 1;  // Prevent division by zero

        avgFrameRate = (u_short)((0x10 << 20) / timeDelta);
        measureStartTime = currTime;
    }

    frameDeltaTime = (u_short)(currTime - frameStartTime);
    
    // Start the next frame
    frameStartTime = currTime;
}

u_long time_getRealTime()
{
    return realTime;
}

u_long time_getFrameNumber()
{
    return frameNumber;
}

u_long time_getFrameTime()
{
    return frameStartTime;
}

u_short time_getDeltaTime()
{
    return frameDeltaTime;
}

u_short time_getFrameRate()
{
    return avgFrameRate;
}