portable/BCC/16BitDOS/PC/port.c

/*
 * 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
 *
 */

/*
 * Changes from V2.6.1
 *
 + Replaced the sUsingPreemption variable with the configUSE_PREEMPTION
 +    macro to be consistent with the later ports.
 +
 + Changes from V4.0.1
 +
 + Add function prvSetTickFrequencyDefault() to set the DOS tick back to
 +    its proper value when the scheduler exits.
 */

#include <stdlib.h>
#include <dos.h>
#include <setjmp.h>

#include "FreeRTOS.h"
#include "task.h"
#include "portasm.h"

/*-----------------------------------------------------------
* Implementation of functions defined in portable.h for the industrial
* PC port.
*----------------------------------------------------------*/

/*lint -e950 Non ANSI reserved words okay in this file only. */

#define portTIMER_INT_NUMBER    0x08

/* Setup hardware for required tick interrupt rate. */
static void prvSetTickFrequency( uint32_t ulTickRateHz );

/* Restore hardware to as it was prior to starting the scheduler. */
static void prvExitFunction( void );

/* Either chain to the DOS tick (which itself clears the PIC) or clear the PIC
 * directly.  We chain to the DOS tick as close as possible to the standard DOS
 * tick rate. */
static void prvPortResetPIC( void );

/* The ISR used depends on whether the preemptive or cooperative
 * scheduler is being used. */
#if ( configUSE_PREEMPTION == 1 )

/* Tick service routine used by the scheduler when preemptive scheduling is
 * being used. */
    static void __interrupt __far prvPreemptiveTick( void );
#else

/* Tick service routine used by the scheduler when cooperative scheduling is
 * being used. */
    static void __interrupt __far prvNonPreemptiveTick( void );
#endif

/* Trap routine used by taskYIELD() to manually cause a context switch. */
static void __interrupt __far prvYieldProcessor( void );

/* Set the tick frequency back so the floppy drive works correctly when the
 * scheduler exits. */
static void prvSetTickFrequencyDefault( void );

/*lint -e956 File scopes necessary here. */

/* Used to signal when to chain to the DOS tick, and when to just clear the PIC ourselves. */
static int16_t    sDOSTickCounter;

/* Set true when the vectors are set so the scheduler will service the tick. */
static BaseType_t xSchedulerRunning = pdFALSE;

/* Points to the original routine installed on the vector we use for manual context switches.  This is then used to restore the original routine during prvExitFunction(). */
static void( __interrupt __far * pxOldSwitchISR )();

/* Points to the original routine installed on the vector we use to chain to the DOS tick.  This is then used to restore the original routine during prvExitFunction(). */
static void( __interrupt __far * pxOldSwitchISRPlus1 )();

/* Used to restore the original DOS context when the scheduler is ended. */
static jmp_buf xJumpBuf;

/*lint +e956 */

/*-----------------------------------------------------------*/
BaseType_t xPortStartScheduler( void )
{
    pxISR pxOriginalTickISR;

    /* This is called with interrupts already disabled. */

    /* Remember what was on the interrupts we are going to use
     * so we can put them back later if required. */
    pxOldSwitchISR      = _dos_getvect( portSWITCH_INT_NUMBER );
    pxOriginalTickISR   = _dos_getvect( portTIMER_INT_NUMBER );
    pxOldSwitchISRPlus1 = _dos_getvect( portSWITCH_INT_NUMBER + 1 );

    prvSetTickFrequency( configTICK_RATE_HZ );

    /* Put our manual switch (yield) function on a known
     * vector. */
    _dos_setvect( portSWITCH_INT_NUMBER, prvYieldProcessor );

    /* Put the old tick on a different interrupt number so we can
     * call it when we want. */
    _dos_setvect( portSWITCH_INT_NUMBER + 1, pxOriginalTickISR );

    /* The ISR used depends on whether the preemptive or cooperative
     * scheduler is being used. */
    #if ( configUSE_PREEMPTION == 1 )
        {
            /* Put our tick switch function on the timer interrupt. */
            _dos_setvect( portTIMER_INT_NUMBER, prvPreemptiveTick );
        }
    #else
        {
            /* We want the timer interrupt to just increment the tick count. */
            _dos_setvect( portTIMER_INT_NUMBER, prvNonPreemptiveTick );
        }
    #endif

    /* Setup a counter that is used to call the DOS interrupt as close
     * to it's original frequency as can be achieved given our chosen tick
     * frequency. */
    sDOSTickCounter     = portTICKS_PER_DOS_TICK;

    /* Clean up function if we want to return to DOS. */
    if( setjmp( xJumpBuf ) != 0 )
    {
        prvExitFunction();
        xSchedulerRunning = pdFALSE;
    }
    else
    {
        xSchedulerRunning = pdTRUE;

        /* Kick off the scheduler by setting up the context of the first task. */
        portFIRST_CONTEXT();
    }

    return xSchedulerRunning;
}
/*-----------------------------------------------------------*/

/* The ISR used depends on whether the preemptive or cooperative
 * scheduler is being used. */
#if ( configUSE_PREEMPTION == 1 )
    static void __interrupt __far prvPreemptiveTick( void )
    {
        /* Get the scheduler to update the task states following the tick. */
        if( xTaskIncrementTick() != pdFALSE )
        {
            /* Switch in the context of the next task to be run. */
            portSWITCH_CONTEXT();
        }

        /* Reset the PIC ready for the next time. */
        prvPortResetPIC();
    }
#else  /* if ( configUSE_PREEMPTION == 1 ) */
    static void __interrupt __far prvNonPreemptiveTick( void )
    {
        /* Same as preemptive tick, but the cooperative scheduler is being used
         * so we don't have to switch in the context of the next task. */
        xTaskIncrementTick();
        prvPortResetPIC();
    }
#endif /* if ( configUSE_PREEMPTION == 1 ) */
/*-----------------------------------------------------------*/

static void __interrupt __far prvYieldProcessor( void )
{
    /* Switch in the context of the next task to be run. */
    portSWITCH_CONTEXT();
}
/*-----------------------------------------------------------*/

static void prvPortResetPIC( void )
{
    /* We are going to call the DOS tick interrupt at as close a
     * frequency to the normal DOS tick as possible. */

    /* WE SHOULD NOT DO THIS IF YIELD WAS CALLED. */
    --sDOSTickCounter;

    if( sDOSTickCounter <= 0 )
    {
        sDOSTickCounter = ( int16_t ) portTICKS_PER_DOS_TICK;
        __asm {
            int portSWITCH_INT_NUMBER + 1
        };
    }
    else
    {
        /* Reset the PIC as the DOS tick is not being called to
         * do it. */
        __asm
        {
            mov al, 20H
            out 20H, al
        };
    }
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
    /* Jump back to the processor state prior to starting the
     * scheduler.  This means we are not going to be using a
     * task stack frame so the task can be deleted. */
    longjmp( xJumpBuf, 1 );
}
/*-----------------------------------------------------------*/

static void prvExitFunction( void )
{
    void( __interrupt __far * pxOriginalTickISR )();

    /* Interrupts should be disabled here anyway - but no
     * harm in making sure. */
    portDISABLE_INTERRUPTS();

    if( xSchedulerRunning == pdTRUE )
    {
        /* Set the DOS tick back onto the timer ticker. */
        pxOriginalTickISR = _dos_getvect( portSWITCH_INT_NUMBER + 1 );
        _dos_setvect( portTIMER_INT_NUMBER, pxOriginalTickISR );
        prvSetTickFrequencyDefault();

        /* Put back the switch interrupt routines that was in place
         * before the scheduler started. */
        _dos_setvect( portSWITCH_INT_NUMBER, pxOldSwitchISR );
        _dos_setvect( portSWITCH_INT_NUMBER + 1, pxOldSwitchISRPlus1 );
    }

    /* The tick timer is back how DOS wants it.  We can re-enable
     * interrupts without the scheduler being called. */
    portENABLE_INTERRUPTS();
}
/*-----------------------------------------------------------*/

static void prvSetTickFrequency( uint32_t ulTickRateHz )
{
    const uint16_t usPIT_MODE        = ( uint16_t ) 0x43;
    const uint16_t usPIT0            = ( uint16_t ) 0x40;
    const uint32_t ulPIT_CONST       = ( uint32_t ) 1193180UL;
    const uint16_t us8254_CTR0_MODE3 = ( uint16_t ) 0x36;
    uint32_t       ulOutput;

    /* Setup the 8245 to tick at the wanted frequency. */
    portOUTPUT_BYTE( usPIT_MODE, us8254_CTR0_MODE3 );
    ulOutput   = ulPIT_CONST / ulTickRateHz;
    portOUTPUT_BYTE( usPIT0, ( uint16_t ) ( ulOutput & ( uint32_t ) 0xff ) );
    ulOutput >>= 8;
    portOUTPUT_BYTE( usPIT0, ( uint16_t ) ( ulOutput & ( uint32_t ) 0xff ) );
}
/*-----------------------------------------------------------*/

static void prvSetTickFrequencyDefault( void )
{
    const uint16_t usPIT_MODE        = ( uint16_t ) 0x43;
    const uint16_t usPIT0            = ( uint16_t ) 0x40;
    const uint16_t us8254_CTR0_MODE3 = ( uint16_t ) 0x36;

    portOUTPUT_BYTE( usPIT_MODE, us8254_CTR0_MODE3 );
    portOUTPUT_BYTE( usPIT0, 0 );
    portOUTPUT_BYTE( usPIT0, 0 );
}


/*lint +e950 */