/*
 * FreeRTOS Kernel V202110.00
 * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * https://www.FreeRTOS.org
 * https://github.com/FreeRTOS
 *
 * 1 tab == 4 spaces!
 */


/*-----------------------------------------------------------
 * Components that can be compiled to either ARM or THUMB mode are
 * contained in port.c  The ISR routines, which can only be compiled
 * to ARM mode, are contained in this file.
 *----------------------------------------------------------*/

/*
*/

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Constants required to handle critical sections. */
#define portNO_CRITICAL_NESTING		( ( uint32_t ) 0 )

volatile uint32_t ulCriticalNesting = 9999UL;

/*-----------------------------------------------------------*/

/* 
 * The scheduler can only be started from ARM mode, hence the inclusion of this
 * function here.
 */
void vPortISRStartFirstTask( void );
/*-----------------------------------------------------------*/

void vPortISRStartFirstTask( void )
{
	/* Simply start the scheduler.  This is included here as it can only be
	called from ARM mode. */
	asm volatile (														\
	"LDR		R0, =pxCurrentTCB								\n\t"	\
	"LDR		R0, [R0]										\n\t"	\
	"LDR		LR, [R0]										\n\t"	\
																		\
	/* The critical nesting depth is the first item on the stack. */	\
	/* Load it into the ulCriticalNesting variable. */					\
	"LDR		R0, =ulCriticalNesting							\n\t"	\
	"LDMFD	LR!, {R1}											\n\t"	\
	"STR		R1, [R0]										\n\t"	\
																		\
	/* Get the SPSR from the stack. */									\
	"LDMFD	LR!, {R0}											\n\t"	\
	"MSR		SPSR, R0										\n\t"	\
																		\
	/* Restore all system mode registers for the task. */				\
	"LDMFD	LR, {R0-R14}^										\n\t"	\
	"NOP														\n\t"	\
																		\
	/* Restore the return address. */									\
	"LDR		LR, [LR, #+60]									\n\t"	\
																		\
	/* And return - correcting the offset in the LR to obtain the */	\
	/* correct address. */												\
	"SUBS PC, LR, #4											\n\t"	\
	);																	
}
/*-----------------------------------------------------------*/

void vPortTickISR( void )
{
	/* Increment the RTOS tick count, then look for the highest priority 
	task that is ready to run. */
	if( xTaskIncrementTick() != pdFALSE )
	{	
		vTaskSwitchContext();
	}
			
	/* Ready for the next interrupt. */
	TB_ClearITPendingBit( TB_IT_Update );	
}

/*-----------------------------------------------------------*/

/*
 * The interrupt management utilities can only be called from ARM mode.  When
 * THUMB_INTERWORK is defined the utilities are defined as functions here to
 * ensure a switch to ARM mode.  When THUMB_INTERWORK is not defined then
 * the utilities are defined as macros in portmacro.h - as per other ports.
 */
#ifdef THUMB_INTERWORK

	void vPortDisableInterruptsFromThumb( void ) __attribute__ ((naked));
	void vPortEnableInterruptsFromThumb( void ) __attribute__ ((naked));

	void vPortDisableInterruptsFromThumb( void )
	{
		asm volatile ( 
			"STMDB	SP!, {R0}		\n\t"	/* Push R0.									*/
			"MRS	R0, CPSR		\n\t"	/* Get CPSR.								*/
			"ORR	R0, R0, #0xC0	\n\t"	/* Disable IRQ, FIQ.						*/
			"MSR	CPSR, R0		\n\t"	/* Write back modified value.				*/
			"LDMIA	SP!, {R0}		\n\t"	/* Pop R0.									*/
			"BX		R14" );					/* Return back to thumb.					*/
	}
			
	void vPortEnableInterruptsFromThumb( void )
	{
		asm volatile ( 
			"STMDB	SP!, {R0}		\n\t"	/* Push R0.									*/	
			"MRS	R0, CPSR		\n\t"	/* Get CPSR.								*/	
			"BIC	R0, R0, #0xC0	\n\t"	/* Enable IRQ, FIQ.							*/	
			"MSR	CPSR, R0		\n\t"	/* Write back modified value.				*/	
			"LDMIA	SP!, {R0}		\n\t"	/* Pop R0.									*/
			"BX		R14" );					/* Return back to thumb.					*/
	}

#endif /* THUMB_INTERWORK */
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
	/* Disable interrupts as per portDISABLE_INTERRUPTS(); 							*/
	asm volatile ( 
		"STMDB	SP!, {R0}			\n\t"	/* Push R0.								*/
		"MRS	R0, CPSR			\n\t"	/* Get CPSR.							*/
		"ORR	R0, R0, #0xC0		\n\t"	/* Disable IRQ, FIQ.					*/
		"MSR	CPSR, R0			\n\t"	/* Write back modified value.			*/
		"LDMIA	SP!, {R0}" );				/* Pop R0.								*/

	/* Now interrupts are disabled ulCriticalNesting can be accessed 
	directly.  Increment ulCriticalNesting to keep a count of how many times
	portENTER_CRITICAL() has been called. */
	ulCriticalNesting++;
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
	if( ulCriticalNesting > portNO_CRITICAL_NESTING )
	{
		/* Decrement the nesting count as we are leaving a critical section. */
		ulCriticalNesting--;

		/* If the nesting level has reached zero then interrupts should be
		re-enabled. */
		if( ulCriticalNesting == portNO_CRITICAL_NESTING )
		{
			/* Enable interrupts as per portEXIT_CRITICAL().					*/
			asm volatile ( 
				"STMDB	SP!, {R0}		\n\t"	/* Push R0.						*/	
				"MRS	R0, CPSR		\n\t"	/* Get CPSR.					*/	
				"BIC	R0, R0, #0xC0	\n\t"	/* Enable IRQ, FIQ.				*/	
				"MSR	CPSR, R0		\n\t"	/* Write back modified value.	*/	
				"LDMIA	SP!, {R0}" );			/* Pop R0.						*/
		}
	}
}