portable/MPLAB/PIC32MEC14xx/ISR_Support.h

/*
 * 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
 *
 */

#include "FreeRTOSConfig.h"

#define portCONTEXT_SIZE             132
#define portEPC_STACK_LOCATION       124
#define portSTATUS_STACK_LOCATION    128

#ifdef __LANGUAGE_ASSEMBLY__

/******************************************************************/
    .macro portSAVE_CONTEXT

/* Make room for the context. First save the current status so it can be
 * manipulated, and the cause and EPC registers so their original values are
 * captured. */
    mfc0 k0, _CP0_CAUSE
    addiu sp, sp, -portCONTEXT_SIZE
    mfc0 k1, _CP0_STATUS

/* Also save s6 and s5 so they can be used.  Any nesting interrupts should
 * maintain the values of these registers across the ISR. */
    sw s6, 44 ( sp )
    sw s5, 40 ( sp )
    sw k1, portSTATUS_STACK_LOCATION( sp )

/* Prepare to enable interrupts above the current priority.
 * k0 = k0 >> 10. Moves RIPL[17:10] to [7:0] */
    srl k0, k0, 0xa

/* Insert bit field. 7 bits k0[6:0] to k1[16:10] */
    ins k1, k0, 10, 7

/* Sets CP0.Status.IPL = CP0.Cause.RIPL
 * Copy the MSB of the IPL, but it would be an error if it was set anyway. */
    srl k0, k0, 0x7

/* MSB of IPL is bit[18] of CP0.Status */
    ins k1, k0, 18, 1

/* CP0.Status[5:1] = 0 b[5]=Rsvd, b[4]=UM,
 * b[3]=Rsvd, b[2]=ERL, b[1]=EXL
 * Setting EXL=0 allows higher priority interrupts
 * to preempt this handler */
    ins k1, zero, 1, 4


/* s5 is used as the frame pointer. */
    add s5, zero, sp

/* Check the nesting count value. */
    la k0, uxInterruptNesting
    lw s6, ( k0 )

/* If the nesting count is 0 then swap to the the system stack, otherwise
 * the system stack is already being used. */
    bne s6, zero, 1f
    nop

/* Swap to the system stack. */
    la sp, xISRStackTop
    lw sp, ( sp )

/* Increment and save the nesting count. */
    1 :  addiu s6, s6, 1
    sw s6, 0 ( k0 )

/* s6 holds the EPC value, this is saved after interrupts are re-enabled. */
    mfc0 s6, _CP0_EPC

/* Re-enable interrupts. */
    mtc0 k1, _CP0_STATUS

/* Save the context into the space just created.  s6 is saved again
 * here as it now contains the EPC value.  No other s registers need be
 * saved. */
    sw ra, 120 ( s5 ) /* Return address (RA=R31) */
    sw s8, 116 ( s5 ) /* Frame Pointer (FP=R30) */
    sw t9, 112 ( s5 )
    sw t8, 108 ( s5 )
    sw t7, 104 ( s5 )
    sw t6, 100 ( s5 )
    sw t5, 96 ( s5 )
    sw t4, 92 ( s5 )
    sw t3, 88 ( s5 )
    sw t2, 84 ( s5 )
    sw t1, 80 ( s5 )
    sw t0, 76 ( s5 )
    sw a3, 72 ( s5 )
    sw a2, 68 ( s5 )
    sw a1, 64 ( s5 )
    sw a0, 60 ( s5 )
    sw v1, 56 ( s5 )
    sw v0, 52 ( s5 )
    sw s6, portEPC_STACK_LOCATION( s5 )
    sw $1, 16 ( s5 )

/* MEC14xx does not have DSP, removed 7 words */
    mfhi s6
    sw s6, 12 ( s5 )
    mflo s6
    sw s6, 8 ( s5 )

/* Update the task stack pointer value if nesting is zero. */
    la s6, uxInterruptNesting
    lw s6, ( s6 )
    addiu s6, s6, -1
    bne s6, zero, 1f
    nop

/* Save the stack pointer. */
    la s6, uxSavedTaskStackPointer
    sw s5, ( s6 )
    1 :
    .endm

/******************************************************************/
       .macro portRESTORE_CONTEXT

/* Restore the stack pointer from the TCB.  This is only done if the
 * nesting count is 1. */
    la s6, uxInterruptNesting
    lw s6, ( s6 )
    addiu s6, s6, -1
    bne s6, zero, 1f
    nop
    la s6, uxSavedTaskStackPointer
    lw s5, ( s6 )

/* Restore the context.
 * MCHP MEC14xx does not include DSP */
    1 :
    lw s6, 8 ( s5 )
    mtlo s6
    lw s6, 12 ( s5 )
    mthi s6
    lw $1, 16 ( s5 )

/* s6 is loaded as it was used as a scratch register and therefore saved
 * as part of the interrupt context. */
    lw s6, 44 ( s5 )
    lw v0, 52 ( s5 )
    lw v1, 56 ( s5 )
    lw a0, 60 ( s5 )
    lw a1, 64 ( s5 )
    lw a2, 68 ( s5 )
    lw a3, 72 ( s5 )
    lw t0, 76 ( s5 )
    lw t1, 80 ( s5 )
    lw t2, 84 ( s5 )
    lw t3, 88 ( s5 )
    lw t4, 92 ( s5 )
    lw t5, 96 ( s5 )
    lw t6, 100 ( s5 )
    lw t7, 104 ( s5 )
    lw t8, 108 ( s5 )
    lw t9, 112 ( s5 )
    lw s8, 116 ( s5 )
    lw ra, 120 ( s5 )

/* Protect access to the k registers, and others. */
    di
    ehb

/* Decrement the nesting count. */
    la k0, uxInterruptNesting
    lw k1, ( k0 )
    addiu k1, k1, -1
    sw k1, 0 ( k0 )

    lw k0, portSTATUS_STACK_LOCATION( s5 )
    lw k1, portEPC_STACK_LOCATION( s5 )

/* Leave the stack in its original state.  First load sp from s5, then
 * restore s5 from the stack. */
    add sp, zero, s5
    lw s5, 40 ( sp )
    addiu sp, sp, portCONTEXT_SIZE

    mtc0 k0, _CP0_STATUS
    mtc0 k1, _CP0_EPC
    ehb
    eret
    nop

       .endm

#endif /* #ifdef __LANGUAGE_ASSEMBLY__ */