/*
 * 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		vTaskSwitchContext
	
.set noat

# Exported to start the first task.
.globl restore_sp_from_pxCurrentTCB		
	
# Entry point for exceptions.
.section .exceptions.entry.user, "xa"

# Save the entire context of a task.
save_context:
	addi	sp,	sp, -116		# Create space on the stack.
	stw		ra, 0(sp)
								# Leave a gap for muldiv 0
	stw		at, 8(sp)		 
	stw		r2, 12(sp)
	stw		r3, 16(sp)
	stw		r4, 20(sp)
	stw		r5, 24(sp) 
	stw		r6, 28(sp) 
	stw		r7, 32(sp) 
	stw		r8, 36(sp) 
	stw		r9, 40(sp) 
	stw		r10, 44(sp)
	stw		r11, 48(sp)
	stw		r12, 52(sp)
	stw		r13, 56(sp)
	stw		r14, 60(sp)
	stw		r15, 64(sp)
	rdctl	r5, estatus 		# Save the eStatus
	stw		r5, 68(sp)
	addi	r15, ea, -4			# Instruction that caused exception
	stw		r15, 72(sp)			# Save as EA
	stw		r16, 76(sp)			# Save the remaining registers
	stw		r17, 80(sp)
	stw		r18, 84(sp)
	stw		r19, 88(sp)
	stw		r20, 92(sp)
	stw		r21, 96(sp)
	stw		r22, 100(sp)
	stw		r23, 104(sp)
	stw		gp, 108(sp)
	stw		fp, 112(sp)

save_sp_to_pxCurrentTCB:
	movia	et, pxCurrentTCB	# Load the address of the pxCurrentTCB pointer
	ldw		et, (et)			# Load the value of the pxCurrentTCB pointer
	stw		sp, (et)			# Store the stack pointer into the top of the TCB

	br		irq_test_user					# skip the section .exceptions.entry

    .section .exceptions.irqtest, "xa"
irq_test_user:

    .section .exceptions.exit.user, "xa"
restore_sp_from_pxCurrentTCB:
	movia	et, pxCurrentTCB		# Load the address of the pxCurrentTCB pointer
	ldw		et, (et)				# Load the value of the pxCurrentTCB pointer
	ldw		sp, (et)				# Load the stack pointer with the top value of the TCB

restore_context:
	ldw		ra, 0(sp)		# Restore the registers.
							# Leave a gap for muldiv 0.
	ldw		at, 8(sp)
	ldw		r2, 12(sp)
	ldw		r3, 16(sp)
	ldw		r4, 20(sp)
	ldw		r5, 24(sp) 
	ldw		r6, 28(sp) 
	ldw		r7, 32(sp) 
	ldw		r8, 36(sp) 
	ldw		r9, 40(sp) 
	ldw		r10, 44(sp)
	ldw		r11, 48(sp)
	ldw		r12, 52(sp)
	ldw		r13, 56(sp)
	ldw		r14, 60(sp)
	ldw		r15, 64(sp)
	ldw		et, 68(sp)		# Load the eStatus
	wrctl	estatus, et 	# Write the eStatus
	ldw		ea, 72(sp)		# Load the Program Counter
	ldw		r16, 76(sp)
	ldw		r17, 80(sp)
	ldw		r18, 84(sp)
	ldw		r19, 88(sp)
	ldw		r20, 92(sp)
	ldw		r21, 96(sp)
	ldw		r22, 100(sp)
	ldw		r23, 104(sp)
	ldw		gp, 108(sp)
	ldw		fp, 112(sp)
	addi	sp,	sp, 116		# Release stack space

    eret					# Return to address ea, loading eStatus into Status.
   
	.section .exceptions.soft, "xa"
soft_exceptions:
	movhi	r3, 0x003b				/* upper half of trap opcode */
	ori		r3, r3, 0x683a			/* lower half of trap opcode */
	beq		r2, r3, call_scheduler
	br		exceptions_unknown_user			# its something else

call_scheduler:
	stw		ea, 72(sp)						# EA is PC+4 so will skip over instruction causing exception
	call	vTaskSwitchContext				# Pick the next context.
	br		restore_sp_from_pxCurrentTCB	# Switch in the task context and restore. 

	.section .exceptions.unknown.user
exceptions_unknown_user:

