[RTOS Support] Confused about prvInitialiseNewTask() function

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Confused about prvInitialiseNewTask() function

Posted by ctc8631 on May 22, 2017

Hello, I'm new freeRTOS learner, I'm trying to understand v9.0 source code about task.c, When I want to create a new task, using xTaskCreate(), it will later call prvInitialiseNewTask(), there are some code I'm confused here,

```

if( portSTACK_GROWTH < 0 )

{ pxTopOfStack = pxNewTCB->pxStack + ( ulStackDepth - ( uint32t ) 1 ); pxTopOfStack = ( StackTypet * ) ( ( ( portPOINTERSIZETYPE ) pxTopOfStack ) & ( ~( ( portPOINTERSIZETYPE ) portBYTEALIGNMENTMASK ) ) ); }

```

I'm not sure why to calculate topStack need to minus 1, I read pxPortInitialiseStack(), and found that everytime it need stack space, it will minus position first, then use space, So I really not sure why to -1 when calculate topStack first time, and need alignment it later, did this waste space?

thanks =)