os_cpu_a.s

UCOS/II for ICCAVR - The version of UCOS/II is 2.04 - the original port was done by Ole Saether

                INC     R16                         ;
                STS     _OSRunning,R16              ;

                LDS     R30,_OSTCBHighRdy           ; Let Z point to TCB of highest priority task
                LDS     R31,_OSTCBHighRdy+1         ; ready to run
                LD      R28,Z+                      ; Load Y (R29:R28) pointer
                LD      R29,Z+                      ;

                POP_SP                              ; Restore stack pointer
                POP_SREG                            ; Restore status register
                POP_ALL                             ; Restore all registers
                RET                                 ; Start task

;/*$PAGE*/.
;********************************************************************************************************
;                                       TASK LEVEL CONTEXT SWITCH
;
; Description : This function is called when a task makes a higher priority task ready-to-run.
;
; Note(s)     : 1) Upon entry,
;                  OSTCBCur     points to the OS_TCB of the task to suspend
;                  OSTCBHighRdy points to the OS_TCB of the task to resume
;
;               2) The stack frame of the task to suspend looks as follows:
;
;                                       SP+0 --> LSB of task code address
;                                         +1     MSB of task code address                (High memory)
;
;               3) The saved context of the task to resume looks as follows:
;
;                  OSTCBHighRdy->OSTCBStkPtr --> SPL of (return) stack pointer           (Low memory)
;                                                SPH of (return) stack pointer
;                                                Flags to load in status register
;                                                R31
;                                                R30
;                                                R27
;                                                .
;                                                .
;                                                R0
;                                                PCH
;                                                PCL                                     (High memory)
;********************************************************************************************************

_OSCtxSw::
                PUSH_ALL                            ; Save current task's context
                PUSH_SREG
                PUSH_SP

                LDS     R30,_OSTCBCur               ; Z = OSTCBCur->OSTCBStkPtr
                LDS     R31,_OSTCBCur+1             ;
                ST      Z+,R28                      ; Save Y (R29:R28) pointer
                ST      Z+,R29                      ;

                CALL    _OSTaskSwHook               ; Call user defined task switch hook

                LDS     R16,_OSPrioHighRdy          ; OSPrioCur = OSPrioHighRdy
                STS     _OSPrioCur,R16

                LDS     R30,_OSTCBHighRdy           ; Let Z point to TCB of highest priority task
                LDS     R31,_OSTCBHighRdy+1         ; ready to run
                STS     _OSTCBCur,R30               ; OSTCBCur = OSTCBHighRdy
                STS     _OSTCBCur+1,R31             ;

                LD      R28,Z+                      ; Restore Y pointer
                LD      R29,Z+                      ;

                POP_SP                              ; Restore stack pointer
                POP_SREG                            ; Restore status register
                POP_ALL                             ; Restore all registers

                RET

;/*$PAGE*/.
;*********************************************************************************************************
;                                INTERRUPT LEVEL CONTEXT SWITCH
;
; Description : This function is called by OSIntExit() to perform a context switch to a task that has
;               been made ready-to-run by an ISR.
;
; Note(s)     : 1) Upon entry,
;                  OSTCBCur     points to the OS_TCB of the task to suspend
;                  OSTCBHighRdy points to the OS_TCB of the task to resume
;
;               2) The stack frame of the task to suspend looks as follows:
;
;                  OSTCBCur->OSTCBStkPtr ------> SPL of (return) stack pointer           (Low memory)
;                                                SPH of (return) stack pointer
;                                                Flags to load in status register
;                                                R31
;                                                R30
;                                                R27
;                                                .
;                                                .
;                                                R0
;                                                PCH
;                                                PCL                                     (High memory)
;
;               3) The saved context of the task to resume looks as follows:
;
;                  OSTCBHighRdy->OSTCBStkPtr --> SPL of (return) stack pointer           (Low memory)
;                                                SPH of (return) stack pointer
;                                                Flags to load in status register
;                                                R31
;                                                R30
;                                                R27
;                                                .
;                                                .
;                                                R0
;                                                PCH
;                                                PCL                                     (High memory)
;*********************************************************************************************************

_OSIntCtxSw::
                CALL    _OSTaskSwHook               ; Call user defined task switch hook

                LDS     R16,_OSPrioHighRdy          ; OSPrioCur = OSPrioHighRdy
                STS     _OSPrioCur,R16              ;

                LDS     R30,_OSTCBHighRdy           ; Z = OSTCBHighRdy->OSTCBStkPtr
                LDS     R31,_OSTCBHighRdy+1         ;
                STS     _OSTCBCur,R30               ; OSTCBCur = OSTCBHighRdy
                STS     _OSTCBCur+1,R31             ;

                LD      R28,Z+                      ; Restore Y pointer
                LD      R29,Z+                      ;

                POP_SP                              ; Restore stack pointer
                POP_SREG                            ; Restore status register
                POP_ALL                             ; Restore all registers
                RET

;/*$PAGE*/.
;********************************************************************************************************
;                                           SYSTEM TICK ISR
;
; Description : This function is the ISR used to notify uC/OS-II that a system tick has occurred.
;
;               The following C-like pseudo-code describe the operation being performed in the code below.
;
;               Save all registers on the current task's stack:
;                      Use the PUSH_ALL macro
;                      Get the SREG, set Bit #7 and save onto the task's stack using -Y addressing
;                      Use the PUSH_SP macro to save the task's hardware stack pointer onto the current task's stack
;               OSIntNesting++;
;               if (OSIntNesting == 1) {
;                  OSTCBCur->OSTCBStkPtr = SP
;               }
;               Clear the interrupt;                  Not needed for the timer we used.
;               OSTimeTick();                         Notify uC/OS-II that a tick has occured
;               OSIntExit();                          Notify uC/OS-II about end of ISR
;               Restore all registers that were save on the current task's stack:
;                      Use the POP_SP macro to restore the task's hardware stack pointer
;                      Use the POP_SREG macro to restore the SREG register
;                      Use the POP_ALL macro to restore the remaining registers
;               Return (DO NOT use a RETI instruction);
;********************************************************************************************************

_OSTickISR::
                PUSH_ALL                            ; Save all registers and status register
                IN      R16,SREG                    ; Save the SREG but with interrupts enabled
                SBR     R16,BIT07                    
                ST      -Y,R16
                PUSH_SP                             ; Save the task's hardware stack pointer onto task's stack

                LDS     R16,_OSIntNesting           ; Notify uC/OS-II of ISR
                INC     R16                         ;
                STS     _OSIntNesting,R16           ;

                CPI     R16,1                       ; if (OSIntNesting == 1) {
                BRNE    OSTickISR_1

                LDS     R30,_OSTCBCur               ;     OSTCBCur->OSTCBStkPtr = Y
                LDS     R31,_OSTCBCur+1
                ST      Z+,R28
                ST      Z+,R29                      ; }

OSTickISR_1:
                CALL    _OSTickISR_Handler          ; Handle the tick ISR

                CALL    _OSIntExit                  ; Notify uC/OS-II about end of ISR

                POP_SP                              ; Restore the hardware stack pointer from task's stack
                POP_SREG                            ; Restore the SREG register
                POP_ALL                             ; Restore all registers

                RET                                 ; Note: RET instead of RETI