;/*
; * Copyright (c) 2006-2018, RT-Thread Development Team
; *
; * SPDX-License-Identifier: Apache-2.0
; *
; * Change Logs:
; * Date           Author       Notes
; * 2010-01-25     Bernard      first version
; * 2012-06-01     aozima       set pendsv priority to 0xFF.
; * 2012-08-17     aozima       fixed bug: store r8 - r11.
; * 2013-06-18     aozima       add restore MSP feature.
; */

;/**
; * @addtogroup CORTEX-M0
; */
;/*@{*/

SCB_VTOR        EQU     0xE000ED08               ; Vector Table Offset Register
NVIC_INT_CTRL   EQU     0xE000ED04               ; interrupt control state register
NVIC_SHPR3      EQU     0xE000ED20               ; system priority register (2)
NVIC_PENDSV_PRI EQU     0xFFFF0000               ; PendSV and SysTick priority value (lowest)
NVIC_PENDSVSET  EQU     0x10000000               ; value to trigger PendSV exception

    SECTION    .text:CODE(2)
    THUMB
    REQUIRE8
    PRESERVE8

    IMPORT rt_thread_switch_interrupt_flag
    IMPORT rt_interrupt_from_thread
    IMPORT rt_interrupt_to_thread

;/*
; * rt_base_t rt_hw_interrupt_disable();
; */
    EXPORT rt_hw_interrupt_disable
rt_hw_interrupt_disable:
    MRS     r0, PRIMASK
    CPSID   I
    BX      LR

;/*
; * void rt_hw_interrupt_enable(rt_base_t level);
; */
    EXPORT  rt_hw_interrupt_enable
rt_hw_interrupt_enable:
    MSR     PRIMASK, r0
    BX      LR

;/*
; * void rt_hw_context_switch(rt_uint32 from, rt_uint32 to);
; * r0 --> from
; * r1 --> to
; */
    EXPORT rt_hw_context_switch_interrupt
    EXPORT rt_hw_context_switch
rt_hw_context_switch_interrupt:
rt_hw_context_switch:
    ; set rt_thread_switch_interrupt_flag to 1
    LDR     r2, =rt_thread_switch_interrupt_flag
    LDR     r3, [r2]
    CMP     r3, #1
    BEQ     _reswitch
    MOVS    r3, #0x1
    STR     r3, [r2]

    LDR     r2, =rt_interrupt_from_thread   ; set rt_interrupt_from_thread
    STR     r0, [r2]

_reswitch
    LDR     r2, =rt_interrupt_to_thread     ; set rt_interrupt_to_thread
    STR     r1, [r2]

    LDR     r0, =NVIC_INT_CTRL              ; trigger the PendSV exception (causes context switch)
    LDR     r1, =NVIC_PENDSVSET
    STR     r1, [r0]
    BX      LR

; r0 --> switch from thread stack
; r1 --> switch to thread stack
; psr, pc, lr, r12, r3, r2, r1, r0 are pushed into [from] stack
    EXPORT PendSV_Handler
PendSV_Handler:

    ; disable interrupt to protect context switch
    MRS     r2, PRIMASK
    CPSID   I

    ; get rt_thread_switch_interrupt_flag
    LDR     r0, =rt_thread_switch_interrupt_flag
    LDR     r1, [r0]
    CMP     r1, #0x00
    BEQ     pendsv_exit                ; pendsv already handled

    ; clear rt_thread_switch_interrupt_flag to 0
    MOVS    r1, #0x00
    STR     r1, [r0]

    LDR     r0, =rt_interrupt_from_thread
    LDR     r1, [r0]
    CMP     r1, #0x00
    BEQ     switch_to_thread        ; skip register save at the first time

    MRS     r1, psp                 ; get from thread stack pointer

    SUBS    r1, r1, #0x20           ; space for {r4 - r7} and {r8 - r11}
    LDR     r0, [r0]
    STR     r1, [r0]                ; update from thread stack pointer

    STMIA   r1!, {r4 - r7}          ; push thread {r4 - r7} register to thread stack

    MOV     r4, r8                  ; mov thread {r8 - r11} to {r4 - r7}
    MOV     r5, r9
    MOV     r6, r10
    MOV     r7, r11
    STMIA   r1!, {r4 - r7}          ; push thread {r8 - r11} high register to thread stack

switch_to_thread
    LDR     r1, =rt_interrupt_to_thread
    LDR     r1, [r1]
    LDR     r1, [r1]                ; load thread stack pointer

    LDMIA   r1!, {r4 - r7}          ; pop thread {r4 - r7} register from thread stack
    PUSH    {r4 - r7}               ; push {r4 - r7} to MSP for copy {r8 - r11}

    LDMIA   r1!, {r4 - r7}          ; pop thread {r8 - r11} high register from thread stack to {r4 - r7}
    MOV     r8,  r4                 ; mov {r4 - r7} to {r8 - r11}
    MOV     r9,  r5
    MOV     r10, r6
    MOV     r11, r7

    POP     {r4 - r7}               ; pop {r4 - r7} from MSP

    MSR     psp, r1                 ; update stack pointer

pendsv_exit
    ; restore interrupt
    MSR     PRIMASK, r2

    MOVS    r0, #0x04
    RSBS    r0, r0, #0x00
    BX      r0

;/*
; * void rt_hw_context_switch_to(rt_uint32 to);
; * r0 --> to
; * this fucntion is used to perform the first thread switch
; */
    EXPORT rt_hw_context_switch_to
rt_hw_context_switch_to:
    ; set to thread
    LDR     r1, =rt_interrupt_to_thread
    STR     r0, [r1]

    ; set from thread to 0
    LDR     r1, =rt_interrupt_from_thread
    MOVS    r0, #0x0
    STR     r0, [r1]

    ; set interrupt flag to 1
    LDR     r1, =rt_thread_switch_interrupt_flag
    MOVS    r0, #1
    STR     r0, [r1]

    ; set the PendSV and SysTick exception priority
    LDR     r0, =NVIC_SHPR3
    LDR     r1, =NVIC_PENDSV_PRI
    LDR     r2, [r0,#0x00]       ; read
    ORRS    r1,r1,r2             ; modify
    STR     r1, [r0]             ; write-back

    ; trigger the PendSV exception (causes context switch)
    LDR     r0, =NVIC_INT_CTRL
    LDR     r1, =NVIC_PENDSVSET
    STR     r1, [r0]
    NOP

    ; restore MSP
    LDR     r0, =SCB_VTOR
    LDR     r0, [r0]
    LDR     r0, [r0]
    NOP
    MSR     msp, r0

    ; enable interrupts at processor level
    CPSIE   I

    ; ensure PendSV exception taken place before subsequent operation
    DSB
    ISB

    ; never reach here!

; compatible with old version
    EXPORT rt_hw_interrupt_thread_switch
rt_hw_interrupt_thread_switch:
    BX      lr

    IMPORT rt_hw_hard_fault_exception
    EXPORT HardFault_Handler
HardFault_Handler:

    ; get current context
    MRS     r0, psp                 ; get fault thread stack pointer
    PUSH    {lr}
    BL      rt_hw_hard_fault_exception
    POP     {pc}

    END