Diff: mbos_asm.s

Revision:

0:a61d29450691

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbos_asm.s	Thu May 05 07:34:12 2011 +0000
@@ -0,0 +1,121 @@
+;***********************************************************************************
+;   m b o s   R T O S   F O R    m b e d  (ARM CORTEX M3) 
+; 
+;  Copyright (c) 2010 - 2011 Andrew Levido
+; 
+;  THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR IMPLIED 
+;  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
+;  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
+;  SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
+;  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
+;  OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+;  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
+;  STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 
+;  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+    EXPORT  _startos    
+    EXPORT  SVC_Handler
+    EXPORT  PendSV_Handler
+    EXPORT  _swap
+
+    EXTERN  _tasklist
+    EXTERN  _tasklistsize
+    EXTERN  _stackerror
+    EXTERN  _hardstacklimit
+
+ID_OFFSET           equ     0               ; 0 word (0byte) offset
+STACK_OFFSET        equ     4               ; 1 word (4byte) offset
+PRIO_OFFSET         equ     8               ; 2 word (8byte) offset
+LIMIT_OFFSET        equ     20              ; 5 word (20byte) offset
+
+    AREA    |.text|, CODE, READONLY, ALIGN=3
+    PRESERVE8
+
+; Function to invoke an SVC exception to start 1st task ----------------------------------
+_startos
+    svc             0                       ; Initiate a system call to start the first task
+    bx              lr                      ; Return (should never happen!)
+    ALIGN
+
+; Function to initiate a SetPend Exception to swap tasks ---------------------------------
+_swap
+    mov             r0, #0xe000e000         ; Base address of ICSR
+    ldr             r1, [r0, #0x0d04]       ; Read ICSR    
+    orr             r1, #0x10000000         ; Set setPend bit
+    str             r1, [r0, #0xd04]        ; write back to ICSR
+    bx              lr
+    ALIGN
+
+; Main task switching and scheduling functions -------------------------------------------
+PendSV_Handler                              ; entered here as handler for context switch
+     cpsid          i                       ; disable interrupts
+    ; save context of running task (that not saved by exception entry)
+    mrs             r0, msp
+    stmdb           r0!, {r4-r11}
+; store the sp in the tcb 
+    ldr             r1, =_tasklist
+    ldr             r1, [r1]
+    ldr             r1, [r1]
+    str             r0, [r1, #STACK_OFFSET]
+; check for stack overflow against task limit
+    ldr             r2, [r1, #LIMIT_OFFSET]
+    cmp             r0, r2
+    bls             stackerror
+; check for stack overflow against hard limit
+    ldr                r2, =_hardstacklimit
+    ldr                r2, [r2]
+    cmp             r0, r2
+    bls                stackerror
+SVC_Handler                                 ; entered here as handler for 1st task start
+    cpsid           i                       ; Disable interrupts
+; sort the task list 
+    ldr             r5, =_tasklist          ; r5 = _tasklist[i] where i = 0
+    ldr             r5, [r5]
+    ldr             r9, =_tasklistsize      ; byte offset of last item in tasklist
+    ldr             r9, [r9]
+    add             r9, r5                  ; outer loop limit
+    sub             r10, r9, #4             ; inner loop limit
+outerloop
+    ldr             r1, [r5]                ; r8 = _tasklist[i]->priostate
+    ldr             r8, [r1, #PRIO_OFFSET]
+    mov             r7, r5                  ; k = i
+    add             r6, r5, #4              ; j = i + 1
+innerloop
+    ldr             r0, [r6]                ; r0 = _tasklist[j]->priostate
+    ldr             r0, [r0, #PRIO_OFFSET]
+    cmp             r0, r8                  ; r0 - r8
+    bcc             innerlooptest           ; branch if r8 higher 
+; found bigger or same!
+    mov             r7, r6                  ; k = j
+    mov             r8, r0                  ; r8 =     _tasklist[j]->priostate
+innerlooptest
+    add             r6, #4                  ; j++
+    cmp             r6, r9                  ; r6 - r9  (j - inner limit)
+    bls             innerloop               ; branch if r9 lower or same
+; swap
+    ldr             r0, [r5]
+    ldr             r1, [r7]
+    str             r1, [r5]
+    str             r0, [r7]
+outerlooptest
+    add             r5, #4                  ; i++
+    cmp             r5, r10                 ; r5 - r10 (i - outer limit)
+    bls             outerloop               ; branch if r10 is lower or same
+    ; restore the context (that not restored by the exception exit) ---------------------
+    ldr             r0, =_tasklist          ; get the sp from the TCB
+    ldr             r0, [r0]
+    ldr             r0, [r0]
+    ldr             r0, [r0, #STACK_OFFSET]
+    ldmia           r0!,{r4-r11}            ; pop the stack
+    msr             msp, r0                 ; and put the sp away
+    cpsie           i                       ; re-enable interrupts
+; Force a return from exception and the restoration of the rest of the regs     
+    bx              lr    
+; A stack error has occurred
+stackerror
+    ldr             r0, [r1, #ID_OFFSET]    ; get id of task into r0
+    bl.w            _stackerror             ; call the C function
+_donothing
+    bl              _donothing
+    ALIGN
+    END
\ No newline at end of file