;********************************************************************************************************
;                                               uC/OS-II
;                                         The Real-Time Kernel
;
;                                       ATmega128  Specific code
;
;
; File     : APP_ISR.S
; By       : Jean J. Labrosse
;********************************************************************************************************

                .include   "os_cpu_i.h"

;/*$PAGE*/.
;********************************************************************************************************
;                                           SYSTEM TICK ISR
;
; Description : This function is the Tick ISR.
;
;               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 from interrupt
;********************************************************************************************************

                .area   text(rel)
                
_BSP_TickISR::
                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    BSP_TickISR_1

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

BSP_TickISR_1:
                CALL    _BSP_TickISR_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_INT                        ; Restore the SREG register
                POP_ALL                             ; Restore all registers

                RETI