/*
 * 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
 *
 */


/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the Tern EE 186
 * port.
 *----------------------------------------------------------*/

/* Library includes. */
#include <embedded.h>
#include <ae.h>

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"
#include "portasm.h"

/* The timer increments every four clocks, hence the divide by 4. */
#define portTIMER_COMPARE ( uint16_t ) ( ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) / ( uint32_t ) 4 )

/* From the RDC data sheet. */
#define portENABLE_TIMER_AND_INTERRUPT ( uint16_t ) 0xe001

/* Interrupt control. */
#define portEIO_REGISTER 0xff22
#define portCLEAR_INTERRUPT 0x0008

/* Setup the hardware to generate the required tick frequency. */
static void prvSetupTimerInterrupt( 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 );

/* The timer initialisation functions leave interrupts enabled,
which is not what we want.  This ISR is installed temporarily in case
the timer fires before we get a change to disable interrupts again. */
static void __interrupt __far prvDummyISR( void );

/*-----------------------------------------------------------*/
/* See header file for description. */
StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
{
StackType_t DS_Reg = 0;

	/* Place a few bytes of known values on the bottom of the stack.
	This is just useful for debugging. */

	*pxTopOfStack = 0x1111;
	pxTopOfStack--;
	*pxTopOfStack = 0x2222;
	pxTopOfStack--;
	*pxTopOfStack = 0x3333;
	pxTopOfStack--;

	/* We are going to start the scheduler using a return from interrupt
	instruction to load the program counter, so first there would be the
	function call with parameters preamble. */
	
	*pxTopOfStack = FP_SEG( pvParameters );
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pvParameters );
	pxTopOfStack--;
	*pxTopOfStack = FP_SEG( pxCode );
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pxCode );
	pxTopOfStack--;

	/* Next the status register and interrupt return address. */
	*pxTopOfStack = portINITIAL_SW;
	pxTopOfStack--;
	*pxTopOfStack = FP_SEG( pxCode );
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pxCode );
	pxTopOfStack--;

	/* The remaining registers would be pushed on the stack by our context
	switch function.  These are loaded with values simply to make debugging
	easier. */
	*pxTopOfStack = ( StackType_t ) 0xAAAA;	/* AX */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0xBBBB;	/* BX */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0xCCCC;	/* CX */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0xDDDD;	/* DX */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0xEEEE;	/* ES */
	pxTopOfStack--;

	/* We need the true data segment. */
	__asm{	MOV DS_Reg, DS };

	*pxTopOfStack = DS_Reg;						/* DS */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0x0123;	/* SI */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0xDDDD;	/* DI */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0xBBBB;	/* BP */

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

BaseType_t xPortStartScheduler( void )
{
	/* This is called with interrupts already disabled. */

	/* Put our manual switch (yield) function on a known
	vector. */
	setvect( portSWITCH_INT_NUMBER, prvYieldProcessor );

	/* Setup the tick interrupt. */
	prvSetupTimerInterrupt();

	/* Kick off the scheduler by setting up the context of the first task. */
	portFIRST_CONTEXT();

	/* Should not get here! */
	return pdFALSE;
}
/*-----------------------------------------------------------*/

static void __interrupt __far prvDummyISR( void )
{
	/* The timer initialisation functions leave interrupts enabled,
	which is not what we want.  This ISR is installed temporarily in case
	the timer fires before we get a change to disable interrupts again. */
	outport( portEIO_REGISTER, portCLEAR_INTERRUPT );
}
/*-----------------------------------------------------------*/

/* 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 interrupt. */
		outport( portEIO_REGISTER, portCLEAR_INTERRUPT );
	}
#else
	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();
		
		/* Reset interrupt. */
		outport( portEIO_REGISTER, portCLEAR_INTERRUPT );
	}
#endif
/*-----------------------------------------------------------*/

static void __interrupt __far prvYieldProcessor( void )
{
	/* Switch in the context of the next task to be run. */
	portSWITCH_CONTEXT();
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* Not implemented. */
}
/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
const uint16_t usTimerACompare = portTIMER_COMPARE, usTimerAMode = portENABLE_TIMER_AND_INTERRUPT;
const uint16_t usT2_IRQ = 0x13;

	/* Configure the timer, the dummy handler is used here as the init
	function leaves interrupts enabled. */
	t2_init( usTimerAMode, usTimerACompare, prvDummyISR );

	/* Disable interrupts again before installing the real handlers. */
	portDISABLE_INTERRUPTS();

	#if( configUSE_PREEMPTION == 1 )
		/* Tick service routine used by the scheduler when preemptive scheduling is
		being used. */
		setvect( usT2_IRQ, prvPreemptiveTick );
	#else
		/* Tick service routine used by the scheduler when cooperative scheduling is
		being used. */
		setvect( usT2_IRQ, prvNonPreemptiveTick );
	#endif
}