/*
 * FreeRTOS Kernel V10.3.1
 * 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.
 *
 * http://www.FreeRTOS.org
 * http://aws.amazon.com/freertos
 *
 * 1 tab == 4 spaces!
 */

/*-----------------------------------------------------------
* Implementation of functions defined in portable.h for the PIC32MX port.
*----------------------------------------------------------*/

#ifndef __XC
    #error This port is designed to work with XC32.  Please update your C compiler version.
#endif

/* Scheduler include files. */
#include "FreeRTOS.h"
#include "task.h"

/* Hardware specifics. */
#define portTIMER_PRESCALE    8
#define portPRESCALE_BITS     1

/* Bits within various registers. */
#define portIE_BIT            ( 0x00000001 )
#define portEXL_BIT           ( 0x00000002 )

/* Bits within the CAUSE register. */
#define portCORE_SW_0         ( 0x00000100 )
#define portCORE_SW_1         ( 0x00000200 )

/* The EXL bit is set to ensure interrupts do not occur while the context of
 * the first task is being restored. */
#define portINITIAL_SR        ( portIE_BIT | portEXL_BIT )

/*
 * By default port.c generates its tick interrupt from TIMER1.  The user can
 * override this behaviour by:
 *  1: Providing their own implementation of vApplicationSetupTickTimerInterrupt(),
 *     which is the function that configures the timer.  The function is defined
 *     as a weak symbol in this file so if the same function name is used in the
 *     application code then the version in the application code will be linked
 *     into the application in preference to the version defined in this file.
 *  2: Define configTICK_INTERRUPT_VECTOR to the vector number of the timer used
 *     to generate the tick interrupt.  For example, when timer 1 is used then
 *     configTICK_INTERRUPT_VECTOR is set to _TIMER_1_VECTOR.
 *     configTICK_INTERRUPT_VECTOR should be defined in FreeRTOSConfig.h.
 *  3: Define configCLEAR_TICK_TIMER_INTERRUPT() to clear the interrupt in the
 *     timer used to generate the tick interrupt.  For example, when timer 1 is
 *     used configCLEAR_TICK_TIMER_INTERRUPT() is defined to
 *     IFS0CLR = _IFS0_T1IF_MASK.
 */
#ifndef configTICK_INTERRUPT_VECTOR
    #define configTICK_INTERRUPT_VECTOR    _TIMER_1_VECTOR
    #define configCLEAR_TICK_TIMER_INTERRUPT()    IFS0CLR = _IFS0_T1IF_MASK
#else
    #ifndef configCLEAR_TICK_TIMER_INTERRUPT
        #error If configTICK_INTERRUPT_VECTOR is defined in application code then configCLEAR_TICK_TIMER_INTERRUPT must also be defined in application code.
    #endif
#endif

/* Let the user override the pre-loading of the initial RA with the address of
 * prvTaskExitError() in case it messes up unwinding of the stack in the
 * debugger - in which case configTASK_RETURN_ADDRESS can be defined as 0 (NULL). */
#ifdef configTASK_RETURN_ADDRESS
    #define portTASK_RETURN_ADDRESS    configTASK_RETURN_ADDRESS
#else
    #define portTASK_RETURN_ADDRESS    prvTaskExitError
#endif

/* Set configCHECK_FOR_STACK_OVERFLOW to 3 to add ISR stack checking to task
 * stack checking.  A problem in the ISR stack will trigger an assert, not call the
 * stack overflow hook function (because the stack overflow hook is specific to a
 * task stack, not the ISR stack). */
#if ( configCHECK_FOR_STACK_OVERFLOW > 2 )

/* Don't use 0xa5 as the stack fill bytes as that is used by the kernerl for
 * the task stacks, and so will legitimately appear in many positions within
 * the ISR stack. */
    #define portISR_STACK_FILL_BYTE    0xee

    static const uint8_t ucExpectedStackBytes[] =
    {
        portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, \
        portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, \
        portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, \
        portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, \
        portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE, portISR_STACK_FILL_BYTE
    }; \

    #define portCHECK_ISR_STACK()    configASSERT( ( memcmp( ( void * ) xISRStack, ( void * ) ucExpectedStackBytes, sizeof( ucExpectedStackBytes ) ) == 0 ) )
#else /* if ( configCHECK_FOR_STACK_OVERFLOW > 2 ) */
    /* Define the function away. */
    #define portCHECK_ISR_STACK()
#endif /* configCHECK_FOR_STACK_OVERFLOW > 2 */

/*-----------------------------------------------------------*/


/*
 * Place the prototype here to ensure the interrupt vector is correctly installed.
 * Note that because the interrupt is written in assembly, the IPL setting in the
 * following line of code has no effect.  The interrupt priority is set by the
 * call to ConfigIntTimer1() in vApplicationSetupTickTimerInterrupt().
 */
extern void __attribute__( ( interrupt( IPL1AUTO ), vector( configTICK_INTERRUPT_VECTOR ) ) ) vPortTickInterruptHandler( void );

/*
 * The software interrupt handler that performs the yield.  Note that, because
 * the interrupt is written in assembly, the IPL setting in the following line of
 * code has no effect.  The interrupt priority is set by the call to
 * mConfigIntCoreSW0() in xPortStartScheduler().
 */
void __attribute__( ( interrupt( IPL1AUTO ), vector( _CORE_SOFTWARE_0_VECTOR ) ) ) vPortYieldISR( void );

/*
 * Used to catch tasks that attempt to return from their implementing function.
 */
static void prvTaskExitError( void );

/*-----------------------------------------------------------*/

/* Records the interrupt nesting depth.  This is initialised to one as it is
 * decremented to 0 when the first task starts. */
volatile UBaseType_t uxInterruptNesting = 0x01;

/* Stores the task stack pointer when a switch is made to use the system stack. */
UBaseType_t uxSavedTaskStackPointer = 0;

/* The stack used by interrupt service routines that cause a context switch. */
__attribute__( ( aligned( 8 ) ) ) StackType_t xISRStack[ configISR_STACK_SIZE ] = { 0 };

/* The top of stack value ensures there is enough space to store 6 registers on
 * the callers stack, as some functions seem to want to do this. */
const StackType_t * const xISRStackTop = &( xISRStack[ ( configISR_STACK_SIZE & ~portBYTE_ALIGNMENT_MASK ) - 8 ] );

/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
                                     TaskFunction_t pxCode,
                                     void * pvParameters )
{
    /* Ensure byte alignment is maintained when leaving this function. */
    pxTopOfStack--;

    *pxTopOfStack = ( StackType_t ) 0xDEADBEEF;
    pxTopOfStack--;

    *pxTopOfStack = ( StackType_t ) 0x12345678; /* Word to which the stack pointer will be left pointing after context restore. */
    pxTopOfStack--;

    *pxTopOfStack = ( StackType_t ) _CP0_GET_CAUSE();
    pxTopOfStack--;

    *pxTopOfStack = ( StackType_t ) portINITIAL_SR; /* CP0_STATUS */
    pxTopOfStack--;

    *pxTopOfStack = ( StackType_t ) pxCode; /* CP0_EPC */
    pxTopOfStack--;

    *pxTopOfStack = ( StackType_t ) portTASK_RETURN_ADDRESS; /* ra */
    pxTopOfStack -= 15;

    *pxTopOfStack = ( StackType_t ) pvParameters; /* Parameters to pass in. */
    pxTopOfStack -= 15;

    return pxTopOfStack;
}
/*-----------------------------------------------------------*/

static void prvTaskExitError( void )
{
    /* A function that implements a task must not exit or attempt to return to
     * its caller as there is nothing to return to.  If a task wants to exit it
     * should instead call vTaskDelete( NULL ).
     *
     * Artificially force an assert() to be triggered if configASSERT() is
     * defined, then stop here so application writers can catch the error. */
    configASSERT( uxSavedTaskStackPointer == 0UL );
    portDISABLE_INTERRUPTS();

    for( ; ; )
    {
    }
}
/*-----------------------------------------------------------*/

/*
 * Setup a timer for a regular tick.  This function uses peripheral timer 1.
 * The function is declared weak so an application writer can use a different
 * timer by redefining this implementation.  If a different timer is used then
 * configTICK_INTERRUPT_VECTOR must also be defined in FreeRTOSConfig.h to
 * ensure the RTOS provided tick interrupt handler is installed on the correct
 * vector number.  When Timer 1 is used the vector number is defined as
 * _TIMER_1_VECTOR.
 */
__attribute__( ( weak ) ) void vApplicationSetupTickTimerInterrupt( void )
{
    const uint32_t ulCompareMatch = ( ( configPERIPHERAL_CLOCK_HZ / portTIMER_PRESCALE ) / configTICK_RATE_HZ ) - 1;

    T1CON = 0x0000;
    T1CONbits.TCKPS = portPRESCALE_BITS;
    PR1 = ulCompareMatch;
    IPC1bits.T1IP = configKERNEL_INTERRUPT_PRIORITY;

    /* Clear the interrupt as a starting condition. */
    IFS0bits.T1IF = 0;

    /* Enable the interrupt. */
    IEC0bits.T1IE = 1;

    /* Start the timer. */
    T1CONbits.TON = 1;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
    /* Not implemented in ports where there is nothing to return to.
     * Artificially force an assert. */
    configASSERT( uxInterruptNesting == 1000UL );
}
/*-----------------------------------------------------------*/

BaseType_t xPortStartScheduler( void )
{
    extern void vPortStartFirstTask( void );
    extern void * pxCurrentTCB;

    #if ( configCHECK_FOR_STACK_OVERFLOW > 2 )
        {
            /* Fill the ISR stack to make it easy to asses how much is being used. */
            memset( ( void * ) xISRStack, portISR_STACK_FILL_BYTE, sizeof( xISRStack ) );
        }
    #endif /* configCHECK_FOR_STACK_OVERFLOW > 2 */

    /* Clear the software interrupt flag. */
    IFS0CLR = _IFS0_CS0IF_MASK;

    /* Set software timer priority. */
    IPC0CLR = _IPC0_CS0IP_MASK;
    IPC0SET = ( configKERNEL_INTERRUPT_PRIORITY << _IPC0_CS0IP_POSITION );

    /* Enable software interrupt. */
    IEC0CLR = _IEC0_CS0IE_MASK;
    IEC0SET = 1 << _IEC0_CS0IE_POSITION;

    /* Setup the timer to generate the tick.  Interrupts will have been
     * disabled by the time we get here. */
    vApplicationSetupTickTimerInterrupt();

    /* Kick off the highest priority task that has been created so far.
     * Its stack location is loaded into uxSavedTaskStackPointer. */
    uxSavedTaskStackPointer = *( UBaseType_t * ) pxCurrentTCB;
    vPortStartFirstTask();

    /* Should never get here as the tasks will now be executing!  Call the task
     * exit error function to prevent compiler warnings about a static function
     * not being called in the case that the application writer overrides this
     * functionality by defining configTASK_RETURN_ADDRESS. */
    prvTaskExitError();

    return pdFALSE;
}
/*-----------------------------------------------------------*/

void vPortIncrementTick( void )
{
    UBaseType_t uxSavedStatus;

    uxSavedStatus = uxPortSetInterruptMaskFromISR();
    {
        if( xTaskIncrementTick() != pdFALSE )
        {
            /* Pend a context switch. */
            _CP0_BIS_CAUSE( portCORE_SW_0 );
        }
    }
    vPortClearInterruptMaskFromISR( uxSavedStatus );

    /* Look for the ISR stack getting near or past its limit. */
    portCHECK_ISR_STACK();

    /* Clear timer interrupt. */
    configCLEAR_TICK_TIMER_INTERRUPT();
}
/*-----------------------------------------------------------*/

UBaseType_t uxPortSetInterruptMaskFromISR( void )
{
    UBaseType_t uxSavedStatusRegister;

    __builtin_disable_interrupts();
    uxSavedStatusRegister = _CP0_GET_STATUS() | 0x01;

    /* This clears the IPL bits, then sets them to
     * configMAX_SYSCALL_INTERRUPT_PRIORITY.  This function should not be called
     * from an interrupt that has a priority above
     * configMAX_SYSCALL_INTERRUPT_PRIORITY so, when used correctly, the action
     * can only result in the IPL being unchanged or raised, and therefore never
     * lowered. */
    _CP0_SET_STATUS( ( ( uxSavedStatusRegister & ( ~portALL_IPL_BITS ) ) ) | ( configMAX_SYSCALL_INTERRUPT_PRIORITY << portIPL_SHIFT ) );

    return uxSavedStatusRegister;
}
/*-----------------------------------------------------------*/

void vPortClearInterruptMaskFromISR( UBaseType_t uxSavedStatusRegister )
{
    _CP0_SET_STATUS( uxSavedStatusRegister );
}
/*-----------------------------------------------------------*/