/*
 * FreeRTOS Kernel <DEVELOPMENT BRANCH>
 * Copyright (C) 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * SPDX-License-Identifier: MIT
 *
 * 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
 *
 */


/* Standard includes. */
#include <stdlib.h>

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

/* Constants required to setup the initial task context. */
#define portINITIAL_SPSR                   ( ( StackType_t ) 0x1f ) /* System mode, ARM mode, interrupts enabled. */
#define portTHUMB_MODE_BIT                 ( ( StackType_t ) 0x20 )
#define portINSTRUCTION_SIZE               ( ( StackType_t ) 4 )
#define portNO_CRITICAL_SECTION_NESTING    ( ( StackType_t ) 0 )

/* Constants required to setup the tick ISR. */
#define portENABLE_TIMER                   ( ( uint8_t ) 0x01 )
#define portPRESCALE_VALUE                 0x00
#define portINTERRUPT_ON_MATCH             ( ( uint32_t ) 0x01 )
#define portRESET_COUNT_ON_MATCH           ( ( uint32_t ) 0x02 )

/* Constants required to setup the VIC for the tick ISR. */
#define portTIMER_VIC_CHANNEL              ( ( uint32_t ) 0x0004 )
#define portTIMER_VIC_CHANNEL_BIT          ( ( uint32_t ) 0x0010 )
#define portTIMER_VIC_ENABLE               ( ( uint32_t ) 0x0020 )

/* Constants required to handle interrupts. */
#define portTIMER_MATCH_ISR_BIT            ( ( uint8_t ) 0x01 )
#define portCLEAR_VIC_INTERRUPT            ( ( uint32_t ) 0 )

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

/* The code generated by the Keil compiler does not maintain separate
 * stack and frame pointers. The portENTER_CRITICAL macro cannot therefore
 * use the stack as per other ports.  Instead a variable is used to keep
 * track of the critical section nesting.  This variable has to be stored
 * as part of the task context and must be initialised to a non zero value. */

#define portNO_CRITICAL_NESTING    ( ( uint32_t ) 0 )
volatile uint32_t ulCriticalNesting = 9999UL;

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

/* Setup the timer to generate the tick interrupts. */
static void prvSetupTimerInterrupt( void );

/*
 * The scheduler can only be started from ARM mode, so
 * vPortStartFirstSTask() is defined in portISR.c.
 */
extern __asm void vPortStartFirstTask( void );

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

/*
 * See header file for description.
 */
StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
                                     TaskFunction_t pxCode,
                                     void * pvParameters )
{
    StackType_t * pxOriginalTOS;

    /* Setup the initial stack of the task.  The stack is set exactly as
     * expected by the portRESTORE_CONTEXT() macro.
     *
     * Remember where the top of the (simulated) stack is before we place
     * anything on it. */
    pxOriginalTOS = pxTopOfStack;

    /* To ensure asserts in tasks.c don't fail, although in this case the assert
     * is not really required. */
    pxTopOfStack--;

    /* First on the stack is the return address - which in this case is the
     * start of the task.  The offset is added to make the return address appear
     * as it would within an IRQ ISR. */
    *pxTopOfStack = ( StackType_t ) pxCode + portINSTRUCTION_SIZE;
    pxTopOfStack--;

    *pxTopOfStack = ( StackType_t ) 0xaaaaaaaa;    /* R14 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) pxOriginalTOS; /* Stack used when task starts goes in R13. */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x12121212;    /* R12 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x11111111;    /* R11 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x10101010;    /* R10 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x09090909;    /* R9 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x08080808;    /* R8 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x07070707;    /* R7 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x06060606;    /* R6 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x05050505;    /* R5 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x04040404;    /* R4 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x03030303;    /* R3 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x02020202;    /* R2 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0x01010101;    /* R1 */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) pvParameters;  /* R0 */
    pxTopOfStack--;

    /* The last thing onto the stack is the status register, which is set for
     * system mode, with interrupts enabled. */
    *pxTopOfStack = ( StackType_t ) portINITIAL_SPSR;

    if( ( ( uint32_t ) pxCode & 0x01UL ) != 0x00UL )
    {
        /* We want the task to start in thumb mode. */
        *pxTopOfStack |= portTHUMB_MODE_BIT;
    }

    pxTopOfStack--;

    /* The code generated by the Keil compiler does not maintain separate
     * stack and frame pointers. The portENTER_CRITICAL macro cannot therefore
     * use the stack as per other ports.  Instead a variable is used to keep
     * track of the critical section nesting.  This variable has to be stored
     * as part of the task context and is initially set to zero. */
    *pxTopOfStack = portNO_CRITICAL_SECTION_NESTING;

    return pxTopOfStack;
}
/*-----------------------------------------------------------*/

BaseType_t xPortStartScheduler( void )
{
    /* Start the timer that generates the tick ISR. */
    prvSetupTimerInterrupt();

    /* Start the first task.  This is done from portISR.c as ARM mode must be
     * used. */
    vPortStartFirstTask();

    /* Should not get here! */
    return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
    /* It is unlikely that the ARM port will require this function as there
     * is nothing to return to.  If this is required - stop the tick ISR then
     * return back to main. */
}
/*-----------------------------------------------------------*/

#if configUSE_PREEMPTION == 0

/*
 * The cooperative scheduler requires a normal IRQ service routine to
 * simply increment the system tick.
 */
    void vNonPreemptiveTick( void ) __irq;
    void vNonPreemptiveTick( void ) __irq
    {
        /* Increment the tick count - this may make a delaying task ready
         * to run - but a context switch is not performed. */
        xTaskIncrementTick();

        T0IR = portTIMER_MATCH_ISR_BIT;        /* Clear the timer event */
        VICVectAddr = portCLEAR_VIC_INTERRUPT; /* Acknowledge the Interrupt */
    }

#else /* if configUSE_PREEMPTION == 0 */

/*
 **************************************************************************
 * The preemptive scheduler ISR is written in assembler and can be found
 * in the portASM.s file. This will only get used if portUSE_PREEMPTION
 * is set to 1 in portmacro.h
 **************************************************************************
 */

    void vPreemptiveTick( void );

#endif /* if configUSE_PREEMPTION == 0 */
/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
    uint32_t ulCompareMatch;

    /* A 1ms tick does not require the use of the timer prescale.  This is
     * defaulted to zero but can be used if necessary. */
    T0PR = portPRESCALE_VALUE;

    /* Calculate the match value required for our wanted tick rate. */
    ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;

    /* Protect against divide by zero.  Using an if() statement still results
     * in a warning - hence the #if. */
    #if portPRESCALE_VALUE != 0
    {
        ulCompareMatch /= ( portPRESCALE_VALUE + 1 );
    }
    #endif

    T0MR0 = ulCompareMatch;

    /* Generate tick with timer 0 compare match. */
    T0MCR = portRESET_COUNT_ON_MATCH | portINTERRUPT_ON_MATCH;

    /* Setup the VIC for the timer. */
    VICIntSelect &= ~( portTIMER_VIC_CHANNEL_BIT );
    VICIntEnable |= portTIMER_VIC_CHANNEL_BIT;

    /* The ISR installed depends on whether the preemptive or cooperative
     * scheduler is being used. */
    #if configUSE_PREEMPTION == 1
    {
        VICVectAddr0 = ( uint32_t ) vPreemptiveTick;
    }
    #else
    {
        VICVectAddr0 = ( uint32_t ) vNonPreemptiveTick;
    }
    #endif

    VICVectCntl0 = portTIMER_VIC_CHANNEL | portTIMER_VIC_ENABLE;

    /* Start the timer - interrupts are disabled when this function is called
     * so it is okay to do this here. */
    T0TCR = portENABLE_TIMER;
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
    /* Disable interrupts as per portDISABLE_INTERRUPTS();                          */
    __disable_irq();

    /* Now that 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(). */
            __enable_irq();
        }
    }
}
/*-----------------------------------------------------------*/