/*
 * FreeRTOS Kernel <DEVELOPMENT BRANCH>
 * 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.
 *
 * https://www.FreeRTOS.org
 * https://github.com/FreeRTOS
 *
 * 1 tab == 4 spaces!
 */

#include "FreeRTOSConfig.h"

#define portCONTEXT_SIZE 132
#define portEPC_STACK_LOCATION	124
#define portSTATUS_STACK_LOCATION 128

/******************************************************************/
.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. */
	srl			k0, k0, 0xa
	ins 		k1, k0, 10, 6
	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)
	sw			s8, 116(s5)
	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)

	/* s6 is used as a scratch register. */
	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. */
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