text: /*
   * FreeRTOS Kernel V10.1.1
   * Copyright (C) 2018 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 NIOS2 port.
   *----------------------------------------------------------*/
  
  /* Standard Includes. */
  #include <string.h>
  #include <errno.h>
  
  /* Altera includes. */
  #include "sys/alt_irq.h"
  #include "altera_avalon_timer_regs.h"
  #include "priv/alt_irq_table.h"
  
  /* Scheduler includes. */
  #include "FreeRTOS.h"
  #include "task.h"
  
  /* Interrupts are enabled. */
  #define portINITIAL_ESTATUS     ( StackType_t ) 0x01 
  
  /*-----------------------------------------------------------*/
  
  /* 
   * Setup the timer to generate the tick interrupts.
   */
  static void prvSetupTimerInterrupt( void );
  
  /*
   * Call back for the alarm function.
   */
  void vPortSysTickHandler( void * context, alt_u32 id );
  
  /*-----------------------------------------------------------*/
  
  static void prvReadGp( uint32_t *ulValue )
  {
  	asm( "stw gp, (%0)" :: "r"(ulValue) );
  }
  /*-----------------------------------------------------------*/
  
  /* 
   * See header file for description. 
   */
  StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
  {    
  StackType_t *pxFramePointer = pxTopOfStack - 1;
  StackType_t xGlobalPointer;
  
      prvReadGp( &xGlobalPointer ); 
  
      /* End of stack marker. */
      *pxTopOfStack = 0xdeadbeef;
      pxTopOfStack--;
      
      *pxTopOfStack = ( StackType_t ) pxFramePointer; 
      pxTopOfStack--;
      
      *pxTopOfStack = xGlobalPointer; 
      
      /* Space for R23 to R16. */
      pxTopOfStack -= 9;
  
      *pxTopOfStack = ( StackType_t ) pxCode; 
      pxTopOfStack--;
  
      *pxTopOfStack = portINITIAL_ESTATUS; 
  
      /* Space for R15 to R5. */    
      pxTopOfStack -= 12;
      
      *pxTopOfStack = ( StackType_t ) pvParameters; 
  
      /* Space for R3 to R1, muldiv and RA. */
      pxTopOfStack -= 5;
      
      return pxTopOfStack;
  }
  /*-----------------------------------------------------------*/
  
  /* 
   * See header file for description. 
   */
  BaseType_t xPortStartScheduler( void )
  {
  	/* Start the timer that generates the tick ISR.  Interrupts are disabled
  	here already. */
  	prvSetupTimerInterrupt();
  	
  	/* Start the first task. */
      asm volatile (  " movia r2, restore_sp_from_pxCurrentTCB        \n"
                      " jmp r2                                          " );
  
  	/* Should not get here! */
  	return 0;
  }
  /*-----------------------------------------------------------*/
  
  void vPortEndScheduler( void )
  {
  	/* It is unlikely that the NIOS2 port will require this function as there
  	is nothing to return to.  */
  }
  /*-----------------------------------------------------------*/
  
  /*
   * Setup the systick timer to generate the tick interrupts at the required
   * frequency.
   */
  void prvSetupTimerInterrupt( void )
  {
  	/* Try to register the interrupt handler. */
  	if ( -EINVAL == alt_irq_register( SYS_CLK_IRQ, 0x0, vPortSysTickHandler ) )
  	{ 
  		/* Failed to install the Interrupt Handler. */
  		asm( "break" );
  	}
  	else
  	{
  		/* Configure SysTick to interrupt at the requested rate. */
  		IOWR_ALTERA_AVALON_TIMER_CONTROL( SYS_CLK_BASE, ALTERA_AVALON_TIMER_CONTROL_STOP_MSK );
  		IOWR_ALTERA_AVALON_TIMER_PERIODL( SYS_CLK_BASE, ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) & 0xFFFF );
  		IOWR_ALTERA_AVALON_TIMER_PERIODH( SYS_CLK_BASE, ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) >> 16 );
  		IOWR_ALTERA_AVALON_TIMER_CONTROL( SYS_CLK_BASE, ALTERA_AVALON_TIMER_CONTROL_CONT_MSK | ALTERA_AVALON_TIMER_CONTROL_START_MSK | ALTERA_AVALON_TIMER_CONTROL_ITO_MSK );	
  	} 
  
  	/* Clear any already pending interrupts generated by the Timer. */
  	IOWR_ALTERA_AVALON_TIMER_STATUS( SYS_CLK_BASE, ~ALTERA_AVALON_TIMER_STATUS_TO_MSK );
  }
  /*-----------------------------------------------------------*/
  
  void vPortSysTickHandler( void * context, alt_u32 id )
  {
  	/* Increment the kernel tick. */
  	if( xTaskIncrementTick() != pdFALSE )
  	{
          vTaskSwitchContext();
  	}
  		
  	/* Clear the interrupt. */
  	IOWR_ALTERA_AVALON_TIMER_STATUS( SYS_CLK_BASE, ~ALTERA_AVALON_TIMER_STATUS_TO_MSK );
  }
  /*-----------------------------------------------------------*/
  
  /** This function is a re-implementation of the Altera provided function.
   * The function is re-implemented to prevent it from enabling an interrupt
   * when it is registered. Interrupts should only be enabled after the FreeRTOS.org
   * kernel has its scheduler started so that contexts are saved and switched 
   * correctly.
   */
  int alt_irq_register( alt_u32 id, void* context, void (*handler)(void*, alt_u32) )
  {
  	int rc = -EINVAL;  
  	alt_irq_context status;
  
  	if (id < ALT_NIRQ)
  	{
  		/* 
  		 * interrupts are disabled while the handler tables are updated to ensure
  		 * that an interrupt doesn't occur while the tables are in an inconsistent
  		 * state.
  		 */
  	
  		status = alt_irq_disable_all ();
  	
  		alt_irq[id].handler = handler;
  		alt_irq[id].context = context;
  	
  		rc = (handler) ? alt_irq_enable (id): alt_irq_disable (id);
  	
  		/* alt_irq_enable_all(status); This line is removed to prevent the interrupt from being immediately enabled. */
  	}
      
  	return rc; 
  }
  /*-----------------------------------------------------------*/
  
  