/*

* Copyright (c) 2008-2009 Nokia Corporation and/or its subsidiary(-ies).

* All rights reserved.

* This component and the accompanying materials are made available

* under the terms of "Eclipse Public License v1.0"

* which accompanies this distribution, and is available

* at the URL "http://www.eclipse.org/legal/epl-v10.html".

*

* Initial Contributors:

* Nokia Corporation - initial contribution.

*

* Contributors:

*

* Description:  

* The frequency of the system timestamp counter in Hz

* The timestamp counter is a 64 bit value which is required to increment at a

* constant rate of at least 1MHz and not to wrap in any reasonable amount of time.

*

*/

const TUint32 KTimestampFrequency = 66666667u;

#ifdef __DEFINE_NKERN_TIMESTAMP_ASM__

/* If NKern::Timestamp() is written in assembler define it here

*/

EXPORT_C __NAKED__ TUint64 NKern::Timestamp()

	{

	// Return a 64 bit high resolution timestamp count

	// Timer 1 counts from 00000000 to FFFFFEFF and then wraps back to 0

	// Timer 2 counts from 00000000 to FFFFFFFF and then wraps back to 0

	// Both timers increment at 66.667MHz (15ns period)

	// Algorithm:

	//		volatile TUint32 t2 = Timer2Count;	// must read t2 first

	//		volatile TUint32 t1 = Timer1Count;

	//		TUint32 n = (t1-t2)>>8;		// number of times T1 has wrapped

	//		return t1 + n * 0xFFFFFF00;

	asm("ldr	r3, 1f ");				// r3 = address of T1 counter

	asm("mrs	r12, cpsr ");

	__ASM_CLI();						// interrupts off

	asm("ldr	r1, [r3, #0x400] ");	// r1 = t2

	asm("ldr	r0, [r3] ");			// r0 = t1

	asm("msr	cpsr, r12 ");			// restore interrupts

	asm("sub	r1, r0, r1 ");			// t1-t2

	asm("mov	r1, r1, lsr #8 ");		// n = (t1-t2)>>8, now have r1:r0 = 2^32*n + t1

	asm("subs	r0, r0, r1, lsl #8 ");	// subtract 256*n

	asm("sbcs	r1, r1, #0 ");			// propagate borrow

	__JUMP(,lr);

	asm("1: ");

#ifdef __MEMMODEL_DIRECT__

	asm(".word 0x18036400 ");				// address of timer 1 counter

#else

	asm(".word 0xC6003400 ");				// address of timer 1 counter

#endif

	}

#endif

#ifdef __DEFINE_NKERN_TIMESTAMP_CPP__

/* If NKern::Timestamp() is written in C++ define it here

*/

#endif