/*
 * 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
 *
 */

	.text
	.arm

	.set SYS_MODE,	0x1f
	.set SVC_MODE,	0x13
	.set IRQ_MODE,	0x12

	/* Variables and functions. */
	.extern ulMaxAPIPriorityMask
	.extern _freertos_vector_table
	.extern pxCurrentTCB
	.extern vTaskSwitchContext
	.extern vApplicationIRQHandler
	.extern ulPortInterruptNesting
	.extern ulPortTaskHasFPUContext
	.extern ulICCEOIR
	.extern ulPortYieldRequired

	.global FreeRTOS_IRQ_Handler
	.global FreeRTOS_SVC_Handler
	.global vPortRestoreTaskContext


.macro portSAVE_CONTEXT

	/* Save the LR and SPSR onto the system mode stack before switching to
	system mode to save the remaining system mode registers. */
	SRSDB	sp!, #SYS_MODE
	CPS		#SYS_MODE
	PUSH	{R0-R12, R14}

	/* Push the critical nesting count. */
	LDR		R2, ulCriticalNestingConst
	LDR		R1, [R2]
	PUSH	{R1}

	/* Does the task have a floating point context that needs saving?  If
	ulPortTaskHasFPUContext is 0 then no. */
	LDR		R2, ulPortTaskHasFPUContextConst
	LDR		R3, [R2]
	CMP		R3, #0

	/* Save the floating point context, if any. */
	FMRXNE  R1,  FPSCR
	VPUSHNE {D0-D15}
#if configFPU_D32 == 1
	VPUSHNE	{D16-D31}
#endif /* configFPU_D32 */
	PUSHNE	{R1}

	/* Save ulPortTaskHasFPUContext itself. */
	PUSH	{R3}

	/* Save the stack pointer in the TCB. */
	LDR		R0, pxCurrentTCBConst
	LDR		R1, [R0]
	STR		SP, [R1]

	.endm

; /**********************************************************************/

.macro portRESTORE_CONTEXT

	/* Set the SP to point to the stack of the task being restored. */
	LDR		R0, pxCurrentTCBConst
	LDR		R1, [R0]
	LDR		SP, [R1]

	/* Is there a floating point context to restore?  If the restored
	ulPortTaskHasFPUContext is zero then no. */
	LDR		R0, ulPortTaskHasFPUContextConst
	POP		{R1}
	STR		R1, [R0]
	CMP		R1, #0

	/* Restore the floating point context, if any. */
	POPNE 	{R0}
#if configFPU_D32 == 1
	VPOPNE	{D16-D31}
#endif /* configFPU_D32 */
	VPOPNE	{D0-D15}
	VMSRNE  FPSCR, R0

	/* Restore the critical section nesting depth. */
	LDR		R0, ulCriticalNestingConst
	POP		{R1}
	STR		R1, [R0]

	/* Restore all system mode registers other than the SP (which is already
	being used). */
	POP		{R0-R12, R14}

	/* Return to the task code, loading CPSR on the way. */
	RFEIA	sp!

	.endm




/******************************************************************************
 * SVC handler is used to yield.
 *****************************************************************************/
.align 4
.type FreeRTOS_SVC_Handler, %function
FreeRTOS_SVC_Handler:
	/* Save the context of the current task and select a new task to run. */
	portSAVE_CONTEXT
	LDR R0, vTaskSwitchContextConst
	BLX	R0
	portRESTORE_CONTEXT


/******************************************************************************
 * vPortRestoreTaskContext is used to start the scheduler.
 *****************************************************************************/
.align 4
.type vPortRestoreTaskContext, %function
vPortRestoreTaskContext:
	/* Switch to system mode. */
	CPS		#SYS_MODE
	portRESTORE_CONTEXT

.align 4
.type FreeRTOS_IRQ_Handler, %function
FreeRTOS_IRQ_Handler:
	/* Return to the interrupted instruction. */
	SUB		lr, lr, #4

	/* Push the return address and SPSR. */
	PUSH	{lr}
	MRS		lr, SPSR
	PUSH	{lr}

	/* Change to supervisor mode to allow reentry. */
	CPS		#0x13

	/* Push used registers. */
	PUSH	{r0-r3, r12}

	/* Increment nesting count.  r3 holds the address of ulPortInterruptNesting
	for future use.  r1 holds the original ulPortInterruptNesting value for
	future use. */
	LDR		r3, ulPortInterruptNestingConst
	LDR		r1, [r3]
	ADD		r0, r1, #1
	STR		r0, [r3]

	/* Ensure bit 2 of the stack pointer is clear.  r2 holds the bit 2 value for
	future use. */
	MOV		r0, sp
	AND		r2, r0, #4
	SUB		sp, sp, r2

	/* Call the interrupt handler. */
	PUSH	{r0-r3, lr}
	LDR		r1, vApplicationIRQHandlerConst
	BLX		r1
	POP		{r0-r3, lr}
	ADD		sp, sp, r2

	CPSID	i
	DSB
	ISB

	/* Write to the EOI register. */
	LDR 	r0, ulICCEOIRConst
	LDR		r2, [r0]
	STR		r0, [r2]

	/* Restore the old nesting count. */
	STR		r1, [r3]

	/* A context switch is never performed if the nesting count is not 0. */
	CMP		r1, #0
	BNE		exit_without_switch

	/* Did the interrupt request a context switch?  r1 holds the address of
	ulPortYieldRequired and r0 the value of ulPortYieldRequired for future
	use. */
	LDR		r1, ulPortYieldRequiredConst
	LDR		r0, [r1]
	CMP		r0, #0
	BNE		switch_before_exit

exit_without_switch:
	/* No context switch.  Restore used registers, LR_irq and SPSR before
	returning. */
	POP		{r0-r3, r12}
	CPS		#IRQ_MODE
	POP		{LR}
	MSR		SPSR_cxsf, LR
	POP		{LR}
	MOVS	PC, LR

switch_before_exit:
	/* A context swtich is to be performed.  Clear the context switch pending
	flag. */
	MOV		r0, #0
	STR		r0, [r1]

	/* Restore used registers, LR-irq and SPSR before saving the context
	to the task stack. */
	POP		{r0-r3, r12}
	CPS		#IRQ_MODE
	POP		{LR}
	MSR		SPSR_cxsf, LR
	POP		{LR}
	portSAVE_CONTEXT

	/* Call the function that selects the new task to execute.
	vTaskSwitchContext() if vTaskSwitchContext() uses LDRD or STRD
	instructions, or 8 byte aligned stack allocated data.  LR does not need
	saving as a new LR will be loaded by portRESTORE_CONTEXT anyway. */
	LDR		R0, vTaskSwitchContextConst
	BLX		R0

	/* Restore the context of, and branch to, the task selected to execute
	next. */
	portRESTORE_CONTEXT

ulICCEOIRConst:	.word ulICCEOIR
pxCurrentTCBConst: .word pxCurrentTCB
ulCriticalNestingConst: .word ulCriticalNesting
ulPortTaskHasFPUContextConst: .word ulPortTaskHasFPUContext
vTaskSwitchContextConst: .word vTaskSwitchContext
vApplicationIRQHandlerConst: .word vApplicationIRQHandler
ulPortInterruptNestingConst: .word ulPortInterruptNesting
ulPortYieldRequiredConst: .word ulPortYieldRequired

.end