/****************************************************************************
 * arch/arm/src/armv8-m/gnu/arm_testset.S
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>
#include <arch/spinlock.h>

	.syntax		unified
	.thumb
	.file	"arm_testset.S"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/****************************************************************************
 * Public Symbols
 ****************************************************************************/

	.globl	up_testset

/****************************************************************************
 * Assembly Macros
 ****************************************************************************/

/****************************************************************************
 * Private Functions
 ****************************************************************************/

	.text

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: up_testset
 *
 * Description:
 *   Perform an atomic test and set operation on the provided spinlock.
 *
 *   This function must be provided via the architecture-specific logic.
 *
 * Input Parameters:
 *   lock - The address of spinlock object.
 *
 * Returned Value:
 *   The spinlock is always locked upon return.  The value of previous value
 *   of the spinlock variable is returned, either SP_LOCKED if the spinlock
 *   as previously locked (meaning that the test-and-set operation failed to
 *   obtain the lock) or SP_UNLOCKED if the spinlock was previously unlocked
 *   (meaning that we successfully obtained the lock)
 *
 ****************************************************************************/

	.globl	up_testset
	.type	up_testset, %function

up_testset:

	mov		r1, #SP_LOCKED

	/* Test if the spinlock is locked or not */

1:
	ldrexb	r2, [r0]			/* Test if spinlock is locked or not */
	cmp		r2, r1				/* Already locked? */
	beq		2f					/* If already locked, return SP_LOCKED */

	/* Not locked ... attempt to lock it */

	strexb	r2, r1, [r0]		/* Attempt to set the locked state */
	cmp		r2, r1				/* r2 will be 1 is strexb failed */
	beq		1b					/* Failed to lock... try again */

	/* Lock acquired -- return SP_UNLOCKED */

	dmb							/* Required before accessing protected resource */
	mov		r0, #SP_UNLOCKED
	bx		lr

	/* Lock not acquired -- return SP_LOCKED */

2:
	mov		r0, #SP_LOCKED
	bx		lr
	.size	up_testset, . - up_testset
	.end