/***************************************************************************
 * This code and information is provided "as is" without warranty of any   *
 * kind, either expressed or implied, including but not limited to the     *
 * implied warranties of merchantability and/or fitness for a particular   *
 * purpose.                                                                *
 *                                                                         *
 * Copyright (C) 2005 Teridian Semiconductor Corp. All Rights Reserved.    *
 ***************************************************************************/
//**************************************************************************
//  DESCRIPTION: 71M652x POWER METER - implement a dual-priority monitor.
//  This implements two priorities: preemptible, and non-preemptible.
//  Since there's only two, priority inversion is impossible.
//  Since the code runs to completion, hangs are impossible
//  Since there's only one locking flag, and thus one order
//  to get it, deadlocks are impossible.
//  Therefore, it's the guts of a very reliable exokernel.
//  Critical regions have to be kept brief, though! 100 microseconds
//  is a recommended maximum.
//  
//  We use this scheme instead of the more typical scheme that
//  just disables a single device's interrupt, because the single
//  device scheme can cause priority inversion.  E.g. a serial
//  interrupt may be disabled in the main loop.  Another device's (a timer...)
//  interrupt preempts the CPU because its interrupt is not locked.
//  The preempting interrupt may be lower priority... and cause
//  the serial interrupt to be delayed so much that data is lost.
// 
//  AUTHOR:  RGV
//
//  HISTORY: See end of file.
//**************************************************************************
//  File: irq.
//
#include "options.h"
#include "irq.h"

/*** External functions used by this module ***/
// None.

/*** External variables used within this module ***/
// None.

/*** Public functions declared within this module ***/
// See irq.h

/*** Public variables declared within this module ***/
// None.

/*** Private functions declared within this module ***/
// None.

/*** Private variables declared within this module ***/
// This uses less space than a system that places
// the interrupt state on the stack.
// It's almost as fast, when reentrant variables are used (as they
// often must be).
bool irq_state = TRUE;    // the "outer" state of a nested set of states.
uint8_t nest_cnt = 0;     // counts nesting of interrupt-disable calls

// This routine should be called at the start of a critical region.
// It disables the interrupt state, and can be called
// from nested subroutine calls.
#pragma save
#pragma NOAREGS
void irq_disable (void) small reentrant
{
    // local variable of a reentrant fn is mutex-safe
    register uint8_t ea_temp;
    ea_temp = EA;        // copy the interrupt state
	IE &= ~EA_;	         // disable all interrupts
    // The increment is done while interrupts are disabled,
    // and is therefore reentrant and mutex-safe, even though it uses
    // a global variable.
    if (nest_cnt++ == 0) // if at the outer call, save the state
    {
        irq_state = ea_temp;
    }
    // otherwise, the interrupt state is managed- discard it.
}
#pragma restore

// This routine should be called at the end of a critical region.
// It restore the interrupt state, and can be called
// from nested subroutine calls.
#pragma save
#pragma NOAREGS
void irq_enable (void) small reentrant
{
    // The decrement is done while interrupts are disabled,
    // and is therefore reentrant and mutex-safe.
    if (--nest_cnt == 0) // if at the outer call, restore the state
    {
  		if (irq_state)   // restore the saved interrupt state
			IE |= EA_;
    }
    // otherwise, the interrupt state is nested, and should
    // remain disabled.
}
#pragma restore

void irq_init (void)
{
    EA = FALSE;        // assure that interrupts start disabled
    irq_state = TRUE;  // and will resume as enabled
    nest_cnt = 1;      // from an unbalanced first call of irq_enable ()
}

/***************************************************************************
 * $Log: irq.c,v $
 * Revision 1.5  2006/09/09 01:15:19  gmikef
 * *** empty log message ***
 *
 * Revision 1.4  2006/01/16 20:11:32  tvander
 * Clean Keil build, all versions
 *
 * Revision 1.2  2005/11/02 21:32:01  gmikef
 * Made IE changes tracible.
 *
 * Revision 1.1  2005/10/08 04:41:32  tvander
 * Fixed priority inversion.
 * Rewrote watchdog to work in brownout, but of course it doesn't work.
 * Watchdog can now be defeated by clearing watchdog option to 0.
 * Reorganized watt hour modules (at last!).
 * Disabled reading of STATUS in 6521_cli because the CE's status is always SAG.
 * Tested with 6521_CLI; measurements seem to work.
 * Fixed other builds.
 *
 *
 * Copyright (C) 2005 Teridian Semiconductor Corp. All Rights Reserved.    *
 * this program is fully protected by the United States copyright          *
 * laws and is the property of Teridian Semiconductor Corporation.         *
 ***************************************************************************/
// events.c