;********************************************************************************************************
;                                               uC/OS-II
;                                         The Real-Time Kernel
;
;                               (c) Copyright 1992-2004, Micrium, Weston, FL
;                                          All Rights Reserved
;
;                                           Generic ARM Port
;
; File      : OS_CPU_A.ASM
; Version   : V1.60
; By        : Jean J. Labrosse
;
; For       : ARM7 or ARM9
; Mode      : ARM or Thumb
; Toolchain : ARM Developer Suite Version 1.2 and higher
;********************************************************************************************************

            IMPORT  OSRunning                    ; External references
            IMPORT  OSPrioCur
            IMPORT  OSPrioHighRdy
            IMPORT  OSTCBCur
            IMPORT  OSTCBHighRdy
            IMPORT  OSIntNesting
            IMPORT  OSIntExit
            IMPORT  OSTaskSwHook
            IMPORT  OSTimeTick
            IMPORT  FIQ_Handler


            EXPORT  OS_CPU_SR_Save               ; Functions declared in this file
            EXPORT  OS_CPU_SR_Restore
            EXPORT  OSStartHighRdy               
            EXPORT  OSCtxSw
            EXPORT  OSIntCtxSw
            EXPORT  OS_CPU_IRQ_ISR
            EXPORT  OS_CPU_FIQ_ISR


NO_INT      EQU     0xC0                         ; Mask used to disable interrupts (Both FIR and IRQ)
FIQ32_MODE  EQU     0x11
IRQ32_MODE  EQU     0x12
SVC32_MODE  EQU     0x13

            AREA    |.text|,CODE

            CODE32

;*********************************************************************************************************
;                                   CRITICAL SECTION METHOD 3 FUNCTIONS
;
; Description: Disable/Enable interrupts by preserving the state of interrupts.  Generally speaking you
;              would store the state of the interrupt disable flag in the local variable 'cpu_sr' and then
;              disable interrupts.  'cpu_sr' is allocated in all of uC/OS-II's functions that need to 
;              disable interrupts.  You would restore the interrupt disable state by copying back 'cpu_sr'
;              into the CPU's status register.
;
; Prototypes :     OS_CPU_SR  OS_CPU_SR_Save(void);
;                  void       OS_CPU_SR_Restore(OS_CPU_SR cpu_sr);
;
;
; Note(s)    : 1) These functions are used in general like this:
;
;                 void Task (void *p_arg)
;                 {
;                 #if OS_CRITICAL_METHOD == 3          /* Allocate storage for CPU status register */
;                     OS_CPU_SR  cpu_sr;
;                 #endif
;
;                          :
;                          :
;                     OS_ENTER_CRITICAL();             /* cpu_sr = OS_CPU_SaveSR();                */
;                          :
;                          :
;                     OS_EXIT_CRITICAL();              /* OS_CPU_RestoreSR(cpu_sr);                */
;                          :
;                          :
;                 }
;
;              2) OS_CPU_SaveSR() is implemented as recommended by Atmel's application note:
;
;                    "Disabling Interrupts at Processor Level"
;*********************************************************************************************************

OS_CPU_SR_Save
        MRS     R0,CPSR                     ; Set IRQ and FIQ bits in CPSR to disable all interrupts
        ORR     R1,R0,#NO_INT
        MSR     CPSR_c,R1
        MRS     R1,CPSR                     ; Confirm that CPSR contains the proper interrupt disable flags
        AND     R1,R1,#NO_INT
        CMP     R1,#NO_INT
        BNE     OS_CPU_SR_Save              ; Not properly disabled (try again)
        BX      LR                          ; Disabled, return the original CPSR contents in R0

OS_CPU_SR_Restore
        MSR     CPSR_c,R0
        BX      LR

;*********************************************************************************************************
;                                          START MULTITASKING
;                                       void OSStartHighRdy(void)
;
; Note(s) : 1) OSStartHighRdy() MUST:
;              a) Call OSTaskSwHook() then,
;              b) Set OSRunning to TRUE,
;              c) Switch to the highest priority task.
;*********************************************************************************************************

OSStartHighRdy

        MSR     CPSR_c, #(NO_INT | SVC32_MODE)
                                        ; Switch to SVC mode with IRQ and FIQ disabled

        LDR     R0, =OSTaskSwHook       ; OSTaskSwHook();
        MOV     LR, PC
        BX      R0            

        LDR     R4, =OSRunning          ; OSRunning = TRUE
        MOV     R5, #1
        STRB    R5, [R4]

                                        ; SWITCH TO HIGHEST PRIORITY TASK
        LDR     R4, =OSTCBHighRdy       ;    Get highest priority task TCB address
        LDR     R4, [R4]                ;    get stack pointer
        LDR     SP, [R4]                ;    switch to the new stack

        LDR     R4,  [SP], #4           ;    pop new task's CPSR
        MSR     SPSR_cxsf,R4
        LDMFD   SP!, {R0-R12,LR,PC}^    ;    pop new task's context

;*********************************************************************************************************
;                         PERFORM A CONTEXT SWITCH (From task level) - OSCtxSw()
;
; Note(s) : 1) OSCtxSw() is called in SYS mode with BOTH FIQ and IRQ interrupts DISABLED
;
;           2) The pseudo-code for OSCtxSw() is:
;              a) Save the current task's context onto the current task's stack
;              b) OSTCBCur->OSTCBStkPtr = SP;
;              c) OSTaskSwHook();
;              d) OSPrioCur             = OSPrioHighRdy;
;              e) OSTCBCur              = OSTCBHighRdy;
;              f) SP                    = OSTCBHighRdy->OSTCBStkPtr;
;              g) Restore the new task's context from the new task's stack
;              h) Return to new task's code
;
;           3) Upon entry: 
;              OSTCBCur      points to the OS_TCB of the task to suspend
;              OSTCBHighRdy  points to the OS_TCB of the task to resume
;*********************************************************************************************************

OSCtxSw
                                        ; SAVE CURRENT TASK'S CONTEXT
        STMFD   SP!, {LR}               ;     Push return address
        STMFD   SP!, {LR}
        STMFD   SP!, {R0-R12}           ;     Push registers
        MRS     R4,  CPSR               ;     Push current CPSR
        TST     LR, #1                  ;     See if called from Thumb mode
        ORRNE   R4,  R4, #0x20          ;     If yes, Set the T-bit
        STMFD   SP!, {R4}
        
        LDR     R4, =OSTCBCur           ; OSTCBCur->OSTCBStkPtr = SP;
        LDR     R5, [R4]
        STR     SP, [R5]

        LDR     R0, =OSTaskSwHook       ; OSTaskSwHook();
        MOV     LR, PC
        BX      R0            

        LDR     R4, =OSPrioCur          ; OSPrioCur = OSPrioHighRdy
        LDR     R5, =OSPrioHighRdy
        LDRB    R6, [R5]
        STRB    R6, [R4]
        
        LDR     R4, =OSTCBCur           ; OSTCBCur  = OSTCBHighRdy;
        LDR     R6, =OSTCBHighRdy
        LDR     R6, [R6]
        STR     R6, [R4]

        LDR     SP, [R6]                ; SP = OSTCBHighRdy->OSTCBStkPtr;

                                        ; RESTORE NEW TASK'S CONTEXT
        LDMFD   SP!, {R4}               ;    Pop new task's CPSR