/*
 * 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
 *
 */

	EXTERN pxCurrentTCB
	EXTERN xSecureContext
	EXTERN vTaskSwitchContext
	EXTERN vPortSVCHandler_C
	EXTERN SecureContext_SaveContext
	EXTERN SecureContext_LoadContext

	PUBLIC xIsPrivileged
	PUBLIC vResetPrivilege
	PUBLIC vPortAllocateSecureContext
	PUBLIC vRestoreContextOfFirstTask
	PUBLIC vRaisePrivilege
	PUBLIC vStartFirstTask
	PUBLIC ulSetInterruptMask
	PUBLIC vClearInterruptMask
	PUBLIC PendSV_Handler
	PUBLIC SVC_Handler
	PUBLIC vPortFreeSecureContext

#if ( configENABLE_FPU == 1 )
	#error Cortex-M23 does not have a Floating Point Unit (FPU) and therefore configENABLE_FPU must be set to 0.
#endif
/*-----------------------------------------------------------*/

/*---------------- Unprivileged Functions -------------------*/

/*-----------------------------------------------------------*/

	SECTION .text:CODE:NOROOT(2)
	THUMB
/*-----------------------------------------------------------*/

xIsPrivileged:
	mrs r0, control							/* r0 = CONTROL. */
	movs r1, #1								/* r1 = 1. */
	tst r0, r1								/* Perform r0 & r1 (bitwise AND) and update the conditions flag. */
	beq running_privileged					/* If the result of previous AND operation was 0, branch. */
	movs r0, #0								/* CONTROL[0]!=0. Return false to indicate that the processor is not privileged. */
	bx lr									/* Return. */
	running_privileged:
		movs r0, #1							/* CONTROL[0]==0. Return true to indicate that the processor is privileged. */
		bx lr								/* Return. */
/*-----------------------------------------------------------*/

vResetPrivilege:
	mrs r0, control							/* r0 = CONTROL. */
	movs r1, #1								/* r1 = 1. */
	orrs r0, r1								/* r0 = r0 | r1. */
	msr control, r0							/* CONTROL = r0. */
	bx lr									/* Return to the caller. */
/*-----------------------------------------------------------*/

vPortAllocateSecureContext:
	svc 0									/* Secure context is allocated in the supervisor call. portSVC_ALLOCATE_SECURE_CONTEXT = 0. */
	bx lr									/* Return. */
/*-----------------------------------------------------------*/

/*----------------- Privileged Functions --------------------*/

/*-----------------------------------------------------------*/

	SECTION privileged_functions:CODE:NOROOT(2)
	THUMB
/*-----------------------------------------------------------*/

vRestoreContextOfFirstTask:
	ldr  r2, =pxCurrentTCB					/* Read the location of pxCurrentTCB i.e. &( pxCurrentTCB ). */
	ldr  r3, [r2]							/* Read pxCurrentTCB. */
	ldr  r0, [r3]							/* Read top of stack from TCB - The first item in pxCurrentTCB is the task top of stack. */

#if ( configENABLE_MPU == 1 )
	dmb										/* Complete outstanding transfers before disabling MPU. */
	ldr r2, =0xe000ed94						/* r2 = 0xe000ed94 [Location of MPU_CTRL]. */
	ldr r4, [r2]							/* Read the value of MPU_CTRL. */
	movs r5, #1								/* r5 = 1. */
	bics r4, r5								/* r4 = r4 & ~r5 i.e. Clear the bit 0 in r4. */
	str r4, [r2]							/* Disable MPU. */

	adds r3, #4								/* r3 = r3 + 4. r3 now points to MAIR0 in TCB. */
	ldr  r4, [r3]							/* r4 = *r3 i.e. r4 = MAIR0. */
	ldr  r2, =0xe000edc0					/* r2 = 0xe000edc0 [Location of MAIR0]. */
	str  r4, [r2]							/* Program MAIR0. */
	ldr  r2, =0xe000ed98					/* r2 = 0xe000ed98 [Location of RNR]. */
	adds r3, #4								/* r3 = r3 + 4. r3 now points to first RBAR in TCB. */
	movs r5, #4								/* r5 = 4. */
	str  r5, [r2]							/* Program RNR = 4. */
	ldmia r3!, {r6,r7}						/* Read first set of RBAR/RLAR from TCB. */
	ldr  r4, =0xe000ed9c					/* r4 = 0xe000ed9c [Location of RBAR]. */
	stmia r4!, {r6,r7}						/* Write first set of RBAR/RLAR registers. */
	movs r5, #5								/* r5 = 5. */
	str  r5, [r2]							/* Program RNR = 5. */
	ldmia r3!, {r6,r7}						/* Read second set of RBAR/RLAR from TCB. */
	ldr  r4, =0xe000ed9c					/* r4 = 0xe000ed9c [Location of RBAR]. */
	stmia r4!, {r6,r7}						/* Write second set of RBAR/RLAR registers. */
	movs r5, #6								/* r5 = 6. */
	str  r5, [r2]							/* Program RNR = 6. */
	ldmia r3!, {r6,r7}						/* Read third set of RBAR/RLAR from TCB. */
	ldr  r4, =0xe000ed9c					/* r4 = 0xe000ed9c [Location of RBAR]. */
	stmia r4!, {r6,r7}						/* Write third set of RBAR/RLAR registers. */
	movs r5, #7								/* r5 = 7. */
	str  r5, [r2]							/* Program RNR = 7. */
	ldmia r3!, {r6,r7}						/* Read fourth set of RBAR/RLAR from TCB. */
	ldr  r4, =0xe000ed9c					/* r4 = 0xe000ed9c [Location of RBAR]. */
	stmia r4!, {r6,r7}						/* Write fourth set of RBAR/RLAR registers. */

	ldr r2, =0xe000ed94						/* r2 = 0xe000ed94 [Location of MPU_CTRL]. */
	ldr r4, [r2]							/* Read the value of MPU_CTRL. */
	movs r5, #1								/* r5 = 1. */
	orrs r4, r5								/* r4 = r4 | r5 i.e. Set the bit 0 in r4. */
	str r4, [r2]							/* Enable MPU. */
	dsb										/* Force memory writes before continuing. */
#endif /* configENABLE_MPU */

#if ( configENABLE_MPU == 1 )
	ldm  r0!, {r1-r4}						/* Read from stack - r1 = xSecureContext, r2 = PSPLIM, r3 = CONTROL and r4 = EXC_RETURN. */
	ldr  r5, =xSecureContext
	str  r1, [r5]							/* Set xSecureContext to this task's value for the same. */
	msr  psplim, r2							/* Set this task's PSPLIM value. */
	msr  control, r3						/* Set this task's CONTROL value. */
	adds r0, #32							/* Discard everything up to r0. */
	msr  psp, r0							/* This is now the new top of stack to use in the task. */
	isb
	bx   r4									/* Finally, branch to EXC_RETURN. */
#else /* configENABLE_MPU */
	ldm  r0!, {r1-r3}						/* Read from stack - r1 = xSecureContext, r2 = PSPLIM and r3 = EXC_RETURN. */
	ldr  r4, =xSecureContext
	str  r1, [r4]							/* Set xSecureContext to this task's value for the same. */
	msr  psplim, r2							/* Set this task's PSPLIM value. */
	movs r1, #2								/* r1 = 2. */
	msr  CONTROL, r1						/* Switch to use PSP in the thread mode. */
	adds r0, #32							/* Discard everything up to r0. */
	msr  psp, r0							/* This is now the new top of stack to use in the task. */
	isb
	bx   r3									/* Finally, branch to EXC_RETURN. */
#endif /* configENABLE_MPU */
/*-----------------------------------------------------------*/

vRaisePrivilege:
	mrs r0, control							/* Read the CONTROL register. */
	movs r1, #1								/* r1 = 1. */
	bics r0, r1								/* Clear the bit 0. */
	msr control, r0							/* Write back the new CONTROL value. */
	bx lr									/* Return to the caller. */
/*-----------------------------------------------------------*/

vStartFirstTask:
	ldr r0, =0xe000ed08						/* Use the NVIC offset register to locate the stack. */
	ldr r0, [r0]							/* Read the VTOR register which gives the address of vector table. */
	ldr r0, [r0]							/* The first entry in vector table is stack pointer. */
	msr msp, r0								/* Set the MSP back to the start of the stack. */
	cpsie i									/* Globally enable interrupts. */
	dsb
	isb
	svc 2									/* System call to start the first task. portSVC_START_SCHEDULER = 2. */
/*-----------------------------------------------------------*/

ulSetInterruptMask:
	mrs r0, PRIMASK
	cpsid i
	bx lr
/*-----------------------------------------------------------*/

vClearInterruptMask:
	msr PRIMASK, r0
	bx lr
/*-----------------------------------------------------------*/

PendSV_Handler:
	mrs r1, psp								/* Read PSP in r1. */
	ldr r2, =xSecureContext					/* Read the location of xSecureContext i.e. &( xSecureContext ). */
	ldr r0, [r2]							/* Read xSecureContext - Value of xSecureContext must be in r0 as it is used as a parameter later. */

	cbz r0, save_ns_context					/* No secure context to save. */
	push {r0-r2, r14}
	bl SecureContext_SaveContext
	pop {r0-r3}								/* LR is now in r3. */
	mov lr, r3								/* LR = r3. */
	lsls r2, r3, #25						/* r2 = r3 << 25. Bit[6] of EXC_RETURN is 1 if secure stack was used, 0 if non-secure stack was used to store stack frame. */
	bpl save_ns_context						/* bpl - branch if positive or zero. If r2 >= 0 ==> Bit[6] in EXC_RETURN is 0 i.e. non-secure stack was used. */
	ldr r3, =pxCurrentTCB					/* Read the location of pxCurrentTCB i.e. &( pxCurrentTCB ). */
	ldr r2, [r3]							/* Read pxCurrentTCB. */
#if ( configENABLE_MPU == 1 )
	subs r1, r1, #16						/* Make space for xSecureContext, PSPLIM, CONTROL and LR on the stack. */
	str r1, [r2]							/* Save the new top of stack in TCB. */
	mrs r2, psplim							/* r2 = PSPLIM. */
	mrs r3, control							/* r3 = CONTROL. */
	mov r4, lr								/* r4 = LR/EXC_RETURN. */
	stmia r1!, {r0, r2-r4}					/* Store xSecureContext, PSPLIM, CONTROL and LR on the stack. */
#else /* configENABLE_MPU */
	subs r1, r1, #12						/* Make space for xSecureContext, PSPLIM and LR on the stack. */
	str r1, [r2]							/* Save the new top of stack in TCB. */
	mrs r2, psplim							/* r2 = PSPLIM. */
	mov r3, lr								/* r3 = LR/EXC_RETURN. */
	stmia r1!, {r0, r2-r3}					/* Store xSecureContext, PSPLIM and LR on the stack. */
#endif /* configENABLE_MPU */
	b select_next_task

	save_ns_context:
		ldr r3, =pxCurrentTCB				/* Read the location of pxCurrentTCB i.e. &( pxCurrentTCB ). */
		ldr r2, [r3]						/* Read pxCurrentTCB. */
	#if ( configENABLE_MPU == 1 )
		subs r1, r1, #48					/* Make space for xSecureContext, PSPLIM, CONTROL, LR and the remaining registers on the stack. */
		str r1, [r2]						/* Save the new top of stack in TCB. */
		adds r1, r1, #16					/* r1 = r1 + 16. */
		stmia r1!, {r4-r7}					/* Store the low registers that are not saved automatically. */
		mov r4, r8							/* r4 = r8. */
		mov r5, r9							/* r5 = r9. */
		mov r6, r10							/* r6 = r10. */
		mov r7, r11							/* r7 = r11. */
		stmia r1!, {r4-r7}					/* Store the high registers that are not saved automatically. */
		mrs r2, psplim						/* r2 = PSPLIM. */
		mrs r3, control						/* r3 = CONTROL. */
		mov r4, lr							/* r4 = LR/EXC_RETURN. */
		subs r1, r1, #48					/* r1 = r1 - 48. */
		stmia r1!, {r0, r2-r4}				/* Store xSecureContext, PSPLIM, CONTROL and LR on the stack. */
	#else /* configENABLE_MPU */
		subs r1, r1, #44					/* Make space for xSecureContext, PSPLIM, LR and the remaining registers on the stack. */
		str r1, [r2]						/* Save the new top of stack in TCB. */
		mrs r2, psplim						/* r2 = PSPLIM. */
		mov r3, lr							/* r3 = LR/EXC_RETURN. */
		stmia r1!, {r0, r2-r7}				/* Store xSecureContext, PSPLIM, LR and the low registers that are not saved automatically. */
		mov r4, r8							/* r4 = r8. */
		mov r5, r9							/* r5 = r9. */
		mov r6, r10							/* r6 = r10. */
		mov r7, r11							/* r7 = r11. */
		stmia r1!, {r4-r7}					/* Store the high registers that are not saved automatically. */
	#endif /* configENABLE_MPU */

	select_next_task:
		cpsid i
		bl vTaskSwitchContext
		cpsie i

		ldr r2, =pxCurrentTCB				/* Read the location of pxCurrentTCB i.e. &( pxCurrentTCB ). */
		ldr r3, [r2]						/* Read pxCurrentTCB. */
		ldr r1, [r3]						/* The first item in pxCurrentTCB is the task top of stack. r1 now points to the top of stack. */

	#if ( configENABLE_MPU == 1 )
		dmb									/* Complete outstanding transfers before disabling MPU. */
		ldr r2, =0xe000ed94					/* r2 = 0xe000ed94 [Location of MPU_CTRL]. */
		ldr r4, [r2]						/* Read the value of MPU_CTRL. */
		movs r5, #1							/* r5 = 1. */
		bics r4, r5							/* r4 = r4 & ~r5 i.e. Clear the bit 0 in r4. */
		str r4, [r2]						/* Disable MPU. */

		adds r3, #4							/* r3 = r3 + 4. r3 now points to MAIR0 in TCB. */
		ldr r4, [r3]						/* r4 = *r3 i.e. r4 = MAIR0. */
		ldr r2, =0xe000edc0					/* r2 = 0xe000edc0 [Location of MAIR0]. */
		str r4, [r2]						/* Program MAIR0. */
		ldr r2, =0xe000ed98					/* r2 = 0xe000ed98 [Location of RNR]. */
		adds r3, #4							/* r3 = r3 + 4. r3 now points to first RBAR in TCB. */
		movs r5, #4							/* r5 = 4. */
		str  r5, [r2]						/* Program RNR = 4. */
		ldmia r3!, {r6,r7}					/* Read first set of RBAR/RLAR from TCB. */
		ldr  r4, =0xe000ed9c				/* r4 = 0xe000ed9c [Location of RBAR]. */
		stmia r4!, {r6,r7}					/* Write first set of RBAR/RLAR registers. */
		movs r5, #5							/* r5 = 5. */
		str  r5, [r2]						/* Program RNR = 5. */
		ldmia r3!, {r6,r7}					/* Read second set of RBAR/RLAR from TCB. */
		ldr  r4, =0xe000ed9c				/* r4 = 0xe000ed9c [Location of RBAR]. */
		stmia r4!, {r6,r7}					/* Write second set of RBAR/RLAR registers. */
		movs r5, #6							/* r5 = 6. */
		str  r5, [r2]						/* Program RNR = 6. */
		ldmia r3!, {r6,r7}					/* Read third set of RBAR/RLAR from TCB. */
		ldr  r4, =0xe000ed9c				/* r4 = 0xe000ed9c [Location of RBAR]. */
		stmia r4!, {r6,r7}					/* Write third set of RBAR/RLAR registers. */
		movs r5, #7							/* r5 = 7. */
		str  r5, [r2]						/* Program RNR = 7. */
		ldmia r3!, {r6,r7}					/* Read fourth set of RBAR/RLAR from TCB. */
		ldr  r4, =0xe000ed9c				/* r4 = 0xe000ed9c [Location of RBAR]. */
		stmia r4!, {r6,r7}					/* Write fourth set of RBAR/RLAR registers. */

		ldr r2, =0xe000ed94					/* r2 = 0xe000ed94 [Location of MPU_CTRL]. */
		ldr r4, [r2]						/* Read the value of MPU_CTRL. */
		movs r5, #1							/* r5 = 1. */
		orrs r4, r5							/* r4 = r4 | r5 i.e. Set the bit 0 in r4. */
		str r4, [r2]						/* Enable MPU. */
		dsb									/* Force memory writes before continuing. */
	#endif /* configENABLE_MPU */

	#if ( configENABLE_MPU == 1 )
		ldmia r1!, {r0, r2-r4}				/* Read from stack - r0 = xSecureContext, r2 = PSPLIM, r3 = CONTROL and r4 = LR. */
		msr psplim, r2						/* Restore the PSPLIM register value for the task. */
		msr control, r3						/* Restore the CONTROL register value for the task. */
		mov lr, r4							/* LR = r4. */
		ldr r2, =xSecureContext				/* Read the location of xSecureContext i.e. &( xSecureContext ). */
		str r0, [r2]						/* Restore the task's xSecureContext. */
		cbz r0, restore_ns_context			/* If there is no secure context for the task, restore the non-secure context. */
		push {r1,r4}
		bl SecureContext_LoadContext		/* Restore the secure context. */
		pop {r1,r4}
		mov lr, r4							/* LR = r4. */
		lsls r2, r4, #25					/* r2 = r4 << 25. Bit[6] of EXC_RETURN is 1 if secure stack was used, 0 if non-secure stack was used to store stack frame. */
		bpl restore_ns_context				/* bpl - branch if positive or zero. If r2 >= 0 ==> Bit[6] in EXC_RETURN is 0 i.e. non-secure stack was used. */
		msr psp, r1							/* Remember the new top of stack for the task. */
		bx lr
	#else /* configENABLE_MPU */
		ldmia r1!, {r0, r2-r3}				/* Read from stack - r0 = xSecureContext, r2 = PSPLIM and r3 = LR. */
		msr psplim, r2						/* Restore the PSPLIM register value for the task. */
		mov lr, r3							/* LR = r3. */
		ldr r2, =xSecureContext				/* Read the location of xSecureContext i.e. &( xSecureContext ). */
		str r0, [r2]						/* Restore the task's xSecureContext. */
		cbz r0, restore_ns_context			/* If there is no secure context for the task, restore the non-secure context. */
		push {r1,r3}
		bl SecureContext_LoadContext		/* Restore the secure context. */
		pop {r1,r3}
		mov lr, r3							/* LR = r3. */
		lsls r2, r3, #25					/* r2 = r3 << 25. Bit[6] of EXC_RETURN is 1 if secure stack was used, 0 if non-secure stack was used to store stack frame. */
		bpl restore_ns_context				/* bpl - branch if positive or zero. If r2 >= 0 ==> Bit[6] in EXC_RETURN is 0 i.e. non-secure stack was used. */
		msr psp, r1							/* Remember the new top of stack for the task. */
		bx lr
	#endif /* configENABLE_MPU */

	restore_ns_context:
		adds r1, r1, #16					/* Move to the high registers. */
		ldmia r1!, {r4-r7}					/* Restore the high registers that are not automatically restored. */
		mov r8, r4							/* r8 = r4. */
		mov r9, r5							/* r9 = r5. */
		mov r10, r6							/* r10 = r6. */
		mov r11, r7							/* r11 = r7. */
		msr psp, r1							/* Remember the new top of stack for the task. */
		subs r1, r1, #32					/* Go back to the low registers. */
		ldmia r1!, {r4-r7}					/* Restore the low registers that are not automatically restored. */
		bx lr
/*-----------------------------------------------------------*/

SVC_Handler:
	movs r0, #4
	mov r1, lr
	tst r0, r1
	beq stacking_used_msp
	mrs r0, psp
	b vPortSVCHandler_C
	stacking_used_msp:
		mrs r0, msp
		b vPortSVCHandler_C
/*-----------------------------------------------------------*/

vPortFreeSecureContext:
	ldr r1, [r0]							/* The first item in the TCB is the top of the stack. */
	ldr r0, [r1]							/* The first item on the stack is the task's xSecureContext. */
	cmp r0, #0								/* Raise svc if task's xSecureContext is not NULL. */
	beq free_secure_context
	bx lr									/* There is no secure context (xSecureContext is NULL). */
	free_secure_context:
		svc 1								/* Secure context is freed in the supervisor call. portSVC_FREE_SECURE_CONTEXT = 1. */
		bx lr								/* Return. */
/*-----------------------------------------------------------*/

	END