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

#define  IN_OS_CPU_C
#include "includes.h"


/*
**********************************************************************************************************
*                                       INITIALIZE A TASK'S STACK
*
* Description: This function is called by either OSTaskCreate() or OSTaskCreateExt() to initialize the
*              stack frame of the task being created. This function is highly processor specific.
*
* Arguments  : task          is a pointer to the task code
*
*              p_arg         is a pointer to a user supplied data area that will be passed to the task
*                            when the task first executes.
*
*              ptos          is a pointer to the top of stack. It is assumed that 'ptos' points to the
*                            highest valid address on the stack.
*
*              opt           specifies options that can be used to alter the behavior of OSTaskStkInit().
*                            (see uCOS_II.H for OS_TASK_OPT_???).
*
* Returns    : Always returns the location of the new top-of-stack' once the processor registers have
*              been placed on the stack in the proper order.
*
* Note(s)    : Interrupts are enabled when your task starts executing. You can change this by setting the
*              SREG to 0x00 instead. In this case, interrupts would be disabled upon task startup. The
*              application code would be responsible for enabling interrupts at the beginning of the task
*              code. You will need to modify OSTaskIdle() and OSTaskStat() so that they enable interrupts.
*              Failure to do this will make your system crash!
*
*              The AVR return stack is placed OS_TASK_STK_SIZE_HARD bytes before the bottom of the task's
*              stack.
**********************************************************************************************************
*/

OS_STK  *OSTaskStkInit (void (*task)(void *pd), void *p_arg, OS_STK *ptos, uint16 opt)
{
    uint8  *psoft_stk;
    uint8  *phard_stk;                      /* Temp. variable used for setting up AVR hardware stack    */
    uint16  tmp;


    (void)opt;                              /* 'opt' is not used, prevent warning                       */
    psoft_stk     = (uint8 *)ptos;
    phard_stk     = (uint8 *)ptos
                  - OSTaskStkSize           /* Task stack size                                          */
                  + OSTaskStkSizeHard;      /* AVR return stack ("hardware stack")                      */
    tmp           = (uint16)task;
                                            /* Put task start address on top of "hardware stack"        */
    *phard_stk--  = (uint8)(tmp & 0xFF);    /* Save PC return address                                   */
    tmp         >>= 8;
    *phard_stk--  = (uint8)(tmp & 0xFF);

    *psoft_stk--  = (uint8)0x00;            /* R0    = 0x00                                             */
    *psoft_stk--  = (uint8)0x01;            /* R1    = 0x01                                             */
    *psoft_stk--  = (uint8)0x02;            /* R2    = 0x02                                             */
    *psoft_stk--  = (uint8)0x03;            /* R3    = 0x03                                             */
    *psoft_stk--  = (uint8)0x04;            /* R4    = 0x04                                             */
    *psoft_stk--  = (uint8)0x05;            /* R5    = 0x05                                             */
    *psoft_stk--  = (uint8)0x06;            /* R6    = 0x06                                             */
    *psoft_stk--  = (uint8)0x07;            /* R7    = 0x07                                             */
    tmp           = (uint16)p_arg;
    *psoft_stk--  = (uint8)tmp;             /* 'p_arg' passed in R17:R16                                */
    *psoft_stk--  = (uint8)(tmp >> 8);
    *psoft_stk--  = (uint8)0x18;            /* R18   = 0x18                                             */
    *psoft_stk--  = (uint8)0x19;            /* R19   = 0x19                                             */
    *psoft_stk--  = (uint8)0x20;            /* R20   = 0x20                                             */
    *psoft_stk--  = (uint8)0x21;            /* R21   = 0x21                                             */
    *psoft_stk--  = (uint8)0x22;            /* R22   = 0x22                                             */
    *psoft_stk--  = (uint8)0x23;            /* R23   = 0x23                                             */
    *psoft_stk--  = (uint8)0x24;            /* R24   = 0x24                                             */
    *psoft_stk--  = (uint8)0x25;            /* R25   = 0x25                                             */
    *psoft_stk--  = (uint8)0x26;            /* R26   = 0x26                                             */
    *psoft_stk--  = (uint8)0x27;            /* R27   = 0x27                                             */
                                            /* R28     R29:R28 is the software stack which gets ...     */
                                            /* R29             ... in the TCB.                          */
    *psoft_stk--  = (uint8)0x30;            /* R30   = 0x30                                             */
    *psoft_stk--  = (uint8)0x31;            /* R31   = 0x31                                             */
    *psoft_stk--  = (uint8)0xAA;            /* RAMPZ = 0xAA                                             */
    *psoft_stk--  = (uint8)0x80;            /* SREG  = Interrupts enabled                               */
    tmp           = (uint16)phard_stk;
    *psoft_stk--  = (uint8)(tmp >> 8);      /* SPH                                                      */
    *psoft_stk    = (uint8)(tmp & 0xFF);    /* SPL                                                      */
    return ((OS_STK *)psoft_stk);
}