{"id":1935,"date":"2019-06-28T04:18:41","date_gmt":"2019-06-28T04:18:41","guid":{"rendered":"http:\/\/fastbitlab.com\/?p=1935"},"modified":"2023-09-08T09:24:06","modified_gmt":"2023-09-08T03:54:06","slug":"free-rtos","status":"publish","type":"post","link":"https:\/\/fastbitlab.com\/blog\/free-rtos\/","title":{"rendered":"How PendSV is used for Context Switching in FreeRTOS ??"},"content":{"rendered":"
\n
\n
\n
\n

 <\/p>\n<\/div>\n

\n

 <\/p>\n

How PendSV is used for Context Switching in FreeRTOS ??<\/span><\/h2>\n
\n
\n
\n<\/div>\n<\/div>\n

Free RTOS<\/strong><\/h3>\n

\"Free<\/p>\n

In this article let me explain, line by line, the<\/p>\n

 PendSV handler which carry out the Context switch form one task to another task. That is nothing but saving the context of current task (Context is nothing but few processor registers, that\u2019s it) and retrieving the context of the next potential task.<\/p>\n

So, here is the handler code, I copied from the port.c<\/strong> file of ARM Cortex M3.<\/strong><\/p>\n

If you want to locate this file then, you have to go to,<\/p>\n

<FreeRTOs installation path>\\FreeRTOS\\FreeRTOSv9.0.0\\FreeRTOS\\Source\\portable\\GCC\\ARM_CM3\\<\/span><\/p>\n

you can download and install the FreeRTOS from here:<\/p>\n

 https:\/\/sourceforge.net\/projects\/freertos\/<\/a><\/strong><\/p>\n

 <\/p>\n

 <\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n
\n

void xPortPendSVHandler( void )<\/span><\/p>\n

{<\/span><\/p>\n

\/* This is a naked function. *\/<\/span><\/p>\n

__asm volatile<\/span><\/p>\n

(<\/span><\/p>\n

“<\/span> mrs r0, psp<\/span> \\n”<\/span><\/p>\n

“<\/span> isb<\/span> \\n”<\/span><\/p>\n

“<\/span> \\n”<\/span><\/p>\n

“<\/span> ldr<\/span> r3, pxCurrentTCBConst<\/span> \\n” \/* Get the location of the current TCB. *\/<\/span><\/span><\/p>\n

“<\/span> ldr<\/span> r2, [r3]<\/span> \\n”<\/span><\/p>\n

“<\/span> \\n”<\/span><\/p>\n

“<\/span> stmdb r0!, {r4-r11}<\/span> \\n” \/* Save the remaining registers. *\/<\/span><\/span><\/p>\n

“<\/span> str r0, [r2]<\/span> \\n” \/* Save the new top of stack into the first member of the TCB. *\/<\/span><\/span><\/p>\n

“<\/span> \\n”<\/span><\/p>\n

“<\/span> stmdb sp!, {r3, r14}<\/span> \\n”<\/span><\/p>\n

“<\/span> mov r0, %0<\/span> \\n”<\/span><\/p>\n

“<\/span> msr basepri, r0<\/span> \\n”<\/span><\/p>\n

“<\/span> bl vTaskSwitchContext<\/span> \\n”<\/span><\/p>\n

“<\/span> mov r0, #0<\/span> \\n”<\/span><\/p>\n

“<\/span> msr basepri, r0<\/span> \\n”<\/span><\/p>\n

“<\/span> ldmia sp!, {r3, r14}<\/span> \\n”<\/span><\/p>\n

“<\/span> \\n”<\/span> \/* Restore the context, including the critical nesting count. *\/<\/span><\/p>\n

“<\/span> ldr r1, [r3]<\/span> \\n”<\/span><\/p>\n

“<\/span> ldr r0, [r1]<\/span> \\n” \/* The first item in pxCurrentTCB is the task top of stack. *\/<\/span><\/span><\/p>\n

“<\/span> ldmia r0!, {r4-r11}<\/span> \\n” \/* Pop the registers. *\/<\/span><\/span><\/p>\n

“<\/span> msr psp, r0<\/span> \\n”<\/span><\/p>\n

“<\/span> isb<\/span> \\n”<\/span><\/p>\n

“<\/span> bx r14<\/span> \\n”<\/span><\/p>\n

“<\/span> \\n”<\/span><\/p>\n

“<\/span> .align 4<\/span> \\n”<\/span><\/p>\n

“pxCurrentTCBConst: .word pxCurrentTCB<\/span> \\n”<\/span><\/p>\n

::”i”(configMAX_SYSCALL_INTERRUPT_PRIORITY)<\/span><\/p>\n

);<\/span><\/p>\n

}<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

Now, let\u2019s explore this line by line.<\/span><\/p>\n

First, i will write the code and below that i will give the explanation !<\/span><\/p>\n

” mrs R0, PSP \\n”<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

Here, they are just saving the PSP value in to R0. Why? Let\u2019s see.<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n
\n

\"\"<\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

” ldr R3, pxCurrentTCBConst \\n”<\/span><\/p>\n

Now, in this line, the address of the global variable \u201cpxCurrentTCB\u201d is stored in R3 register.<\/span><\/p>\n

\u201cpxCurrentTCB\u201d is a global variable defined in tasks.c (go ahead and check tasks.c) which holds the address of the Currently executing task\u2019s TCB.<\/span><\/p>\n

Now, let\u2019s just assume that the address of the pxCurrentTCB is 0x20000000. And it is holding the address 0x20001108 as shown below.<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

\"\"<\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

So, now <\/span>R3<\/b> = 0x20000000<\/span><\/p>\n

” ldr R2, [R3] \\n”<\/span><\/p>\n

(De-reference 0x20000000 and store the value into R2)<\/span><\/p>\n

So, R2 = 0x20001108 (Address of the Current TCB)<\/span><\/p>\n

” stmdb R0!, {R4-R11} \\n”<\/span><\/p>\n

Now , R0 has PSP value right ??  So, using that PSP, we are saving the registers contents R4 to R11 on to the tasks stack memory. So, currently R4 to R11 are safe.<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n
\n

\"\"<\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

” str R0, [R2] \\n”<\/span><\/p>\n

(De-reference 0x20001108 and store the value in to R0)<\/span><\/p>\n

What is 0x20001108? It\u2019s the address of the current TCB stored in pxCurrentTCB pointer.<\/span><\/p>\n

That is, pxCurrentTCB is nothing but a pointer of type \u201ctskTCB\u201d.<\/span><\/p>\n

tskTCB is the TCB structure which is defined in tasks.c. Go Go Go check tasks.c !!! . You will find the below structure.<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

\/*<\/span><\/p>\n

 * Task control block.  A task control block (TCB) is allocated for each task,<\/span><\/p>\n

 * and stores task state information, including a pointer to the task’s context<\/span><\/p>\n

 * (the task’s run time environment, including register values)<\/span><\/p>\n

 *\/<\/span><\/p>\n

typedef struct tskTaskControlBlock<\/span><\/p>\n

{<\/span><\/p>\n

volatile StackType_t<\/span> *pxTopOfStack;<\/span> \/*< Points to the location of the last item placed on the tasks stack.  THIS MUST BE THE FIRST MEMBER OF THE TCB STRUCT. *\/<\/span><\/p>\n

#if ( portUSING_MPU_WRAPPERS == 1 )<\/span><\/p>\n

xMPU_SETTINGS<\/span> xMPUSettings;<\/span> \/*< The MPU settings are defined as part of the port layer.  THIS MUST BE THE SECOND MEMBER OF THE TCB STRUCT. *\/<\/span><\/p>\n

#endif<\/span><\/p>\n

ListItem_t<\/span> xStateListItem;<\/span> \/*< The list that the state list item of a task is reference from denotes the state of that task (Ready, Blocked, Suspended ). *\/<\/span><\/p>\n

ListItem_t<\/span> xEventListItem;<\/span> \/*< Used to reference a task from an event list. *\/<\/span><\/p>\n

UBaseType_t<\/span> uxPriority;<\/span> \/*< The priority of the task.  0 is the lowest priority. *\/<\/span><\/p>\n

StackType_t<\/span> *pxStack;<\/span> \/*< Points to the start of the stack. *\/<\/span><\/p>\n

char<\/span> pcTaskName[ configMAX_TASK_NAME_LEN ];\/*< Descriptive name given to the task when created.  Facilitates debugging only. *\/ \/*lint !e971 Unqualified char types are allowed for strings and single characters only. *\/<\/span><\/span><\/p>\n

#if ( portSTACK_GROWTH > 0 )<\/span><\/p>\n

StackType_t<\/span> *pxEndOfStack;<\/span> \/*< Points to the end of the stack on architectures where the stack grows up from low memory. *\/<\/span><\/p>\n

#endif<\/span><\/p>\n

#if ( portCRITICAL_NESTING_IN_TCB == 1 )<\/span><\/p>\n

UBaseType_t<\/span> uxCriticalNesting;<\/span> \/*< Holds the critical section nesting depth for ports that do not maintain their own count in the port layer. *\/<\/span><\/p>\n

#endif<\/span><\/p>\n

#if ( configUSE_TRACE_FACILITY == 1 )<\/span><\/p>\n

UBaseType_t<\/span> uxTCBNumber;<\/span> \/*< Stores a number that increments each time a TCB is created.  It allows debuggers to determine when a task has been deleted and then recreated. *\/<\/span><\/p>\n

UBaseType_t<\/span> uxTaskNumber;<\/span> \/*< Stores a number specifically for use by third party trace code. *\/<\/span><\/p>\n

#endif<\/span><\/p>\n

#if ( configUSE_MUTEXES == 1 )<\/span><\/p>\n

UBaseType_t<\/span> uxBasePriority;<\/span> \/*< The priority last assigned to the task – used by the priority inheritance mechanism. *\/<\/span><\/p>\n

UBaseType_t<\/span> uxMutexesHeld;<\/span><\/p>\n

#endif<\/span><\/p>\n

#if ( configUSE_APPLICATION_TASK_TAG == 1 )<\/span><\/p>\n

TaskHookFunction_t pxTaskTag;<\/span><\/p>\n

#endif<\/span><\/p>\n

#if( configNUM_THREAD_LOCAL_STORAGE_POINTERS > 0 )<\/span><\/p>\n

void *pvThreadLocalStoragePointers[ configNUM_THREAD_LOCAL_STORAGE_POINTERS ];<\/span><\/p>\n

#endif<\/span><\/p>\n

#if( configGENERATE_RUN_TIME_STATS == 1 )<\/span><\/p>\n

uint32_t<\/span> ulRunTimeCounter;<\/span> \/*< Stores the amount of time the task has spent in the Running state. *\/<\/span><\/p>\n

#endif<\/span><\/p>\n

#if ( configUSE_NEWLIB_REENTRANT == 1 )<\/span><\/p>\n

\/* Allocate a Newlib reent structure that is specific to this task.<\/span><\/p>\n

Note Newlib support has been included by popular demand, but is not<\/span><\/p>\n

used by the FreeRTOS maintainers themselves.  FreeRTOS is not<\/span><\/p>\n

responsible for resulting newlib operation.  User must be familiar with<\/span><\/p>\n

newlib and must provide system-wide implementations of the necessary<\/span><\/p>\n

stubs. Be warned that (at the time of writing) the current newlib design<\/span><\/p>\n

implements a system-wide malloc() that must be provided with locks. *\/<\/span><\/p>\n

struct<\/span> _reent xNewLib_reent;<\/span><\/p>\n

#endif<\/span><\/p>\n

#if( configUSE_TASK_NOTIFICATIONS == 1 )<\/span><\/p>\n

volatile uint32_t ulNotifiedValue;<\/span><\/p>\n

volatile uint8_t ucNotifyState;<\/span><\/p>\n

#endif<\/span><\/p>\n

\/* See the comments above the definition of<\/span><\/p>\n

tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE. *\/<\/span><\/p>\n

#if( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 )<\/span><\/p>\n

uint8_t<\/span> ucStaticallyAllocated; <\/span> \/*< Set to pdTRUE if the task is a statically allocated to ensure no attempt is made to free the memory. *\/<\/span><\/p>\n

#endif<\/span><\/p>\n

#if( INCLUDE_xTaskAbortDelay == 1 )<\/span><\/p>\n

uint8_t ucDelayAborted;<\/span><\/p>\n

#endif<\/span><\/p>\n

} tskTCB;<\/span><\/p>\n

 <\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

In this structure take look in to the first member. What\u2019s that??<\/span><\/p>\n

It\u2019s another pointer isn\u2019t? Or you can say a place holder, which holds address of the stack where the last item is placed by this task and remember that every task will have its own stack space.<\/span><\/p>\n

So, the first member just holds the address of the last item present in the stack.<\/span><\/p>\n

After \u201c<\/span>stmdb R0!, {R4-R11} , R0\u2033<\/b> will be pointing to the new top of the stack isn\u2019t it ??<\/span><\/p>\n

So, save that new top of the stack in to the first member of the TCB.<\/span><\/p>\n

Now, the first member of the TCB is updated with new top of the stack. i.e. value in the register R0.<\/span><\/p>\n

This value will be used to restore the stack pointer, when this task switches in later point in time.<\/span><\/p>\n

Ok. let\u2019s move ahead.<\/span><\/p>\n

“<\/span> stmdb sp!, {R3, R14}<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

We are going to branch out after this, that\u2019s why, save R3 and R14 for a time being.<\/span><\/p>\n

R0 is already saved, no worries!<\/span><\/p>\n

R1 is not required because we didn\u2019t used it so far,<\/span><\/p>\n

R2 was just a place holder, now it\u2019s not required, so only save R3 and R14.<\/span><\/p>\n

Note that here SP being used, since we are in the handler mode of the processor, SP is nothing but MSP (Main Stack Pointer).<\/span><\/p>\n

So, we just pushed to kernels stack memory.<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n
\n

\"\"<\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n

“<\/span> mov R0, %0<\/span> \\n”<\/span><\/p>\n

“<\/span> msr basepri, R0<\/span> \\n”<\/span><\/p>\n

\/* disable the interrupts, *\/<\/span><\/p>\n

“<\/span> bl vTaskSwitchContext<\/span> \\n”<\/span><\/p>\n

 <\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n
\n

branch out to <\/span>vTaskSwitchContext.<\/b><\/p>\n

vTaskSwitchContext<\/b> is defined in tasks.c , which selects the next potential task based on priority .<\/span><\/p>\n

So, the below figure explains what happens when call is made to <\/span>vTaskSwitchContext<\/b>.<\/span><\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n
\n

\"\"<\/p>\n<\/div>\n

<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n<\/div>\n
\n
<\/div>\n
\n
    \n
  1. Initially the global pointer <\/span>pxCurrentTCB<\/b> was holding the address of the Current TCB .i.e <\/span>0x20001108<\/b><\/li>\n
  2. After that call is made to <\/span>vTaskSwitchContext<\/b><\/li>\n
  3. Inside <\/span>vTaskSwitchContext<\/b> , there is a call to <\/span>taskSELECT_HIGHEST_PRIORITY_TASK()<\/b><\/li>\n
  4. Which changes the pxCurrentTCB<\/b> value to the address of the next potential TCB<\/li>\n<\/ol>\n

    “<\/span> mov R0, #0<\/span> \\n”<\/span><\/p>\n

    ” msr basepri, R0         \\n”<\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    Disables the interrupt again, who knows what happened to basepri when we branched out above *\/<\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    “<\/span> ldmia sp!, {R3, R14}<\/span> \\n”<\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    POP R3 , R14.<\/span><\/p>\n

    Remember that R3 = 0X20000000<\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    \"\"<\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    ” ldr R1, [R3] \\n”<\/span><\/p>\n

    Dereference R3, and store the value in to R1.<\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    \"\"<\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    “<\/span> ldr R0, [R1]<\/span> \\n”<\/span><\/p>\n

     <\/p>\n

    Dereference 0x20000580 and store the value in to R0 .<\/span><\/p>\n

    That means, store the value of the first member of the new TCB.<\/span><\/p>\n

    As you already know, first member is nothing but top of the stack.<\/span><\/p>\n

    So, R0 = Top of the stack of new Task, which is selected for switching in.<\/span><\/p>\n

    “<\/span> ldmia R0!, {R4-R11}<\/span> \\n”<\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    <\/div>\n
    \n
    <\/div>\n
    \n

    So, we know the top of the stack;<\/span><\/p>\n

    Let\u2019s use that to retrieve the context of new Task.<\/span><\/p>\n

    This is the Current Stack state of the New Task which is about to switch in!<\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    \"\"<\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    This is the Current Stack state of the New Task after \u201cldmia R0!, {R4-R11}\u201d<\/b><\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    \"\"<\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    So, context of the new task is retrieved to register <\/span>R4<\/b> to <\/span>R11<\/b>.<\/span><\/p>\n

    “<\/span> msr PSP, R0<\/span> \\n”<\/span><\/p>\n

    Now, let\u2019s initialize the PSP with the R0 value.<\/span><\/p>\n

    “<\/span> bx R14<\/span> \\n”<\/span><\/p>\n

    Return from the handler!<\/span><\/p>\n

     <\/p>\n

    Before executing \u201cbx R14\u201d<\/b><\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    \"\"<\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    After executing bx R14<\/b><\/span><\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    \"\"<\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n
    \n

    So, the task will resume to the instruction during which it was switched out of the running state.<\/b><\/span><\/p>\n

    Note: I have omitted explaining of \u201cISB\u201d instruction. Please, read from here<\/b><\/span><\/p>\n

    http:\/\/infocenter.arm.com\/help\/index.jsp?topic=\/com.arm.doc.dui0552a\/CHDEBIEG.html<\/b><\/a><\/span><\/p>\n

    Get the Full Course on FreeRTOS Porting and programming  <\/b>Here.<\/b><\/a><\/span><\/span><\/p>\n

    If you like this article, please consider sharing it in linkedin by clicking below.<\/b><\/span><\/p>\n

    Thanks.<\/b><\/span><\/p>\n<\/div>\n

    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

        How PendSV is used for Context Switching in FreeRTOS ?? Free RTOS In this article let me explain, line by line, the  PendSV handler which carry out the Context switch form one task to another task. That is nothing but saving the context of current task (Context is nothing but few processor registers, […]<\/p>\n","protected":false},"author":1,"featured_media":431,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ocean_post_layout":"","ocean_both_sidebars_style":"","ocean_both_sidebars_content_width":0,"ocean_both_sidebars_sidebars_width":0,"ocean_sidebar":"0","ocean_second_sidebar":"0","ocean_disable_margins":"enable","ocean_add_body_class":"","ocean_shortcode_before_top_bar":"","ocean_shortcode_after_top_bar":"","ocean_shortcode_before_header":"","ocean_shortcode_after_header":"","ocean_has_shortcode":"","ocean_shortcode_after_title":"","ocean_shortcode_before_footer_widgets":"","ocean_shortcode_after_footer_widgets":"","ocean_shortcode_before_footer_bottom":"","ocean_shortcode_after_footer_bottom":"","ocean_display_top_bar":"default","ocean_display_header":"default","ocean_header_style":"","ocean_center_header_left_menu":"0","ocean_custom_header_template":"0","ocean_custom_logo":0,"ocean_custom_retina_logo":0,"ocean_custom_logo_max_width":0,"ocean_custom_logo_tablet_max_width":0,"ocean_custom_logo_mobile_max_width":0,"ocean_custom_logo_max_height":0,"ocean_custom_logo_tablet_max_height":0,"ocean_custom_logo_mobile_max_height":0,"ocean_header_custom_menu":"0","ocean_menu_typo_font_family":"0","ocean_menu_typo_font_subset":"","ocean_menu_typo_font_size":0,"ocean_menu_typo_font_size_tablet":0,"ocean_menu_typo_font_size_mobile":0,"ocean_menu_typo_font_size_unit":"px","ocean_menu_typo_font_weight":"","ocean_menu_typo_font_weight_tablet":"","ocean_menu_typo_font_weight_mobile":"","ocean_menu_typo_transform":"","ocean_menu_typo_transform_tablet":"","ocean_menu_typo_transform_mobile":"","ocean_menu_typo_line_height":0,"ocean_menu_typo_line_height_tablet":0,"ocean_menu_typo_line_height_mobile":0,"ocean_menu_typo_line_height_unit":"","ocean_menu_typo_spacing":0,"ocean_menu_typo_spacing_tablet":0,"ocean_menu_typo_spacing_mobile":0,"ocean_menu_typo_spacing_unit":"","ocean_menu_link_color":"","ocean_menu_link_color_hover":"","ocean_menu_link_color_active":"","ocean_menu_link_background":"","ocean_menu_link_hover_background":"","ocean_menu_link_active_background":"","ocean_menu_social_links_bg":"","ocean_menu_social_hover_links_bg":"","ocean_menu_social_links_color":"","ocean_menu_social_hover_links_color":"","ocean_disable_title":"default","ocean_disable_heading":"default","ocean_post_title":"","ocean_post_subheading":"","ocean_post_title_style":"","ocean_post_title_background_color":"","ocean_post_title_background":0,"ocean_post_title_bg_image_position":"","ocean_post_title_bg_image_attachment":"","ocean_post_title_bg_image_repeat":"","ocean_post_title_bg_image_size":"","ocean_post_title_height":0,"ocean_post_title_bg_overlay":0.5,"ocean_post_title_bg_overlay_color":"","ocean_disable_breadcrumbs":"default","ocean_breadcrumbs_color":"","ocean_breadcrumbs_separator_color":"","ocean_breadcrumbs_links_color":"","ocean_breadcrumbs_links_hover_color":"","ocean_display_footer_widgets":"default","ocean_display_footer_bottom":"default","ocean_custom_footer_template":"0","ocean_post_oembed":"","ocean_post_self_hosted_media":"","ocean_post_video_embed":"","ocean_link_format":"","ocean_link_format_target":"self","ocean_quote_format":"","ocean_quote_format_link":"post","ocean_gallery_link_images":"off","ocean_gallery_id":[],"footnotes":""},"categories":[8],"tags":[],"class_list":["post-1935","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","entry","has-media"],"yoast_head":"\nHow PendSV is used for Context Switching in FreeRTOS ??<\/title>\n<meta name=\"description\" content=\"Context switching in Free RTOS. In this article let me explain, line by line, the PendSV handler which carry out the Context switch form one task to another\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/fastbitlab.com\/blog\/free-rtos\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"How PendSV is used for Context Switching in FreeRTOS ??\" \/>\n<meta property=\"og:description\" content=\"Context switching in Free RTOS. In this article let me explain, line by line, the PendSV handler which carry out the Context switch form one task to another\" \/>\n<meta property=\"og:url\" content=\"https:\/\/fastbitlab.com\/blog\/free-rtos\/\" \/>\n<meta property=\"og:site_name\" content=\"FastBit EBA\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/fastbiteba\/\" \/>\n<meta property=\"article:published_time\" content=\"2019-06-28T04:18:41+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2023-09-08T03:54:06+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2017\/03\/free1.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"330\" \/>\n\t<meta property=\"og:image:height\" content=\"125\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"FastBitLab\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@fastbiteba\" \/>\n<meta name=\"twitter:site\" content=\"@fastbiteba\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"FastBitLab\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"9 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/\"},\"author\":{\"name\":\"FastBitLab\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#\\\/schema\\\/person\\\/e32b38e733a0d76ffa7e6bc998652e5d\"},\"headline\":\"How PendSV is used for Context Switching in FreeRTOS ??\",\"datePublished\":\"2019-06-28T04:18:41+00:00\",\"dateModified\":\"2023-09-08T03:54:06+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/\"},\"wordCount\":1650,\"commentCount\":7,\"publisher\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/03\\\/free1.jpg\",\"articleSection\":[\"Blog\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/\",\"url\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/\",\"name\":\"How PendSV is used for Context Switching in FreeRTOS ??\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/03\\\/free1.jpg\",\"datePublished\":\"2019-06-28T04:18:41+00:00\",\"dateModified\":\"2023-09-08T03:54:06+00:00\",\"description\":\"Context switching in Free RTOS. In this article let me explain, line by line, the PendSV handler which carry out the Context switch form one task to another\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#primaryimage\",\"url\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/03\\\/free1.jpg\",\"contentUrl\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/03\\\/free1.jpg\",\"width\":330,\"height\":125},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/free-rtos\\\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"How PendSV is used for Context Switching in FreeRTOS ??\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#website\",\"url\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/\",\"name\":\"FastBit EBA\",\"description\":\"Your Online Academy of Embedded Systems\",\"publisher\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Organization\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#organization\",\"name\":\"FastBit EBA\",\"url\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#\\\/schema\\\/logo\\\/image\\\/\",\"url\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/wp-content\\\/uploads\\\/2026\\\/04\\\/logo-EzNrEnyr.png\",\"contentUrl\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/wp-content\\\/uploads\\\/2026\\\/04\\\/logo-EzNrEnyr.png\",\"width\":640,\"height\":640,\"caption\":\"FastBit EBA\"},\"image\":{\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#\\\/schema\\\/logo\\\/image\\\/\"},\"sameAs\":[\"https:\\\/\\\/www.facebook.com\\\/fastbiteba\\\/\",\"https:\\\/\\\/x.com\\\/fastbiteba\",\"https:\\\/\\\/www.linkedin.com\\\/in\\\/fastbit-embedded-brain-academy-b3167b124\\\/\",\"https:\\\/\\\/www.youtube.com\\\/channel\\\/UCa1REBV9hyrzGp2mjJCagBg\"]},{\"@type\":\"Person\",\"@id\":\"https:\\\/\\\/fastbitlab.com\\\/blog\\\/#\\\/schema\\\/person\\\/e32b38e733a0d76ffa7e6bc998652e5d\",\"name\":\"FastBitLab\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/9230d0f9bdef28b63a01e7ca274ee7b2e8ed9abe932ee564af8809caaf52a0c8?s=96&d=mm&r=g\",\"url\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/9230d0f9bdef28b63a01e7ca274ee7b2e8ed9abe932ee564af8809caaf52a0c8?s=96&d=mm&r=g\",\"contentUrl\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/9230d0f9bdef28b63a01e7ca274ee7b2e8ed9abe932ee564af8809caaf52a0c8?s=96&d=mm&r=g\",\"caption\":\"FastBitLab\"},\"description\":\"The FastBit Embedded Brain Academy uses the power of internet to bring the online courses related to the field of embedded system programming, Real time operating system, Embedded Linux systems, etc at your finger tip with very low cost. Backed with strong experience of industry, we have produced lots of courses with the customer enrolment over 3000+ across 100+ countries.\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"How PendSV is used for Context Switching in FreeRTOS ??","description":"Context switching in Free RTOS. In this article let me explain, line by line, the PendSV handler which carry out the Context switch form one task to another","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/fastbitlab.com\/blog\/free-rtos\/","og_locale":"en_US","og_type":"article","og_title":"How PendSV is used for Context Switching in FreeRTOS ??","og_description":"Context switching in Free RTOS. In this article let me explain, line by line, the PendSV handler which carry out the Context switch form one task to another","og_url":"https:\/\/fastbitlab.com\/blog\/free-rtos\/","og_site_name":"FastBit EBA","article_publisher":"https:\/\/www.facebook.com\/fastbiteba\/","article_published_time":"2019-06-28T04:18:41+00:00","article_modified_time":"2023-09-08T03:54:06+00:00","og_image":[{"width":330,"height":125,"url":"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2017\/03\/free1.jpg","type":"image\/jpeg"}],"author":"FastBitLab","twitter_card":"summary_large_image","twitter_creator":"@fastbiteba","twitter_site":"@fastbiteba","twitter_misc":{"Written by":"FastBitLab","Est. reading time":"9 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/#article","isPartOf":{"@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/"},"author":{"name":"FastBitLab","@id":"https:\/\/fastbitlab.com\/blog\/#\/schema\/person\/e32b38e733a0d76ffa7e6bc998652e5d"},"headline":"How PendSV is used for Context Switching in FreeRTOS ??","datePublished":"2019-06-28T04:18:41+00:00","dateModified":"2023-09-08T03:54:06+00:00","mainEntityOfPage":{"@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/"},"wordCount":1650,"commentCount":7,"publisher":{"@id":"https:\/\/fastbitlab.com\/blog\/#organization"},"image":{"@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/#primaryimage"},"thumbnailUrl":"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2017\/03\/free1.jpg","articleSection":["Blog"],"inLanguage":"en-US","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/fastbitlab.com\/blog\/free-rtos\/#respond"]}]},{"@type":"WebPage","@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/","url":"https:\/\/fastbitlab.com\/blog\/free-rtos\/","name":"How PendSV is used for Context Switching in FreeRTOS ??","isPartOf":{"@id":"https:\/\/fastbitlab.com\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/#primaryimage"},"image":{"@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/#primaryimage"},"thumbnailUrl":"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2017\/03\/free1.jpg","datePublished":"2019-06-28T04:18:41+00:00","dateModified":"2023-09-08T03:54:06+00:00","description":"Context switching in Free RTOS. In this article let me explain, line by line, the PendSV handler which carry out the Context switch form one task to another","breadcrumb":{"@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/fastbitlab.com\/blog\/free-rtos\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/#primaryimage","url":"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2017\/03\/free1.jpg","contentUrl":"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2017\/03\/free1.jpg","width":330,"height":125},{"@type":"BreadcrumbList","@id":"https:\/\/fastbitlab.com\/blog\/free-rtos\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/fastbitlab.com\/blog\/"},{"@type":"ListItem","position":2,"name":"How PendSV is used for Context Switching in FreeRTOS ??"}]},{"@type":"WebSite","@id":"https:\/\/fastbitlab.com\/blog\/#website","url":"https:\/\/fastbitlab.com\/blog\/","name":"FastBit EBA","description":"Your Online Academy of Embedded Systems","publisher":{"@id":"https:\/\/fastbitlab.com\/blog\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/fastbitlab.com\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/fastbitlab.com\/blog\/#organization","name":"FastBit EBA","url":"https:\/\/fastbitlab.com\/blog\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/fastbitlab.com\/blog\/#\/schema\/logo\/image\/","url":"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2026\/04\/logo-EzNrEnyr.png","contentUrl":"https:\/\/fastbitlab.com\/blog\/wp-content\/uploads\/2026\/04\/logo-EzNrEnyr.png","width":640,"height":640,"caption":"FastBit EBA"},"image":{"@id":"https:\/\/fastbitlab.com\/blog\/#\/schema\/logo\/image\/"},"sameAs":["https:\/\/www.facebook.com\/fastbiteba\/","https:\/\/x.com\/fastbiteba","https:\/\/www.linkedin.com\/in\/fastbit-embedded-brain-academy-b3167b124\/","https:\/\/www.youtube.com\/channel\/UCa1REBV9hyrzGp2mjJCagBg"]},{"@type":"Person","@id":"https:\/\/fastbitlab.com\/blog\/#\/schema\/person\/e32b38e733a0d76ffa7e6bc998652e5d","name":"FastBitLab","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/secure.gravatar.com\/avatar\/9230d0f9bdef28b63a01e7ca274ee7b2e8ed9abe932ee564af8809caaf52a0c8?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/9230d0f9bdef28b63a01e7ca274ee7b2e8ed9abe932ee564af8809caaf52a0c8?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/9230d0f9bdef28b63a01e7ca274ee7b2e8ed9abe932ee564af8809caaf52a0c8?s=96&d=mm&r=g","caption":"FastBitLab"},"description":"The FastBit Embedded Brain Academy uses the power of internet to bring the online courses related to the field of embedded system programming, Real time operating system, Embedded Linux systems, etc at your finger tip with very low cost. Backed with strong experience of industry, we have produced lots of courses with the customer enrolment over 3000+ across 100+ countries."}]}},"_links":{"self":[{"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/posts\/1935","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/comments?post=1935"}],"version-history":[{"count":5,"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/posts\/1935\/revisions"}],"predecessor-version":[{"id":15861,"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/posts\/1935\/revisions\/15861"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/media\/431"}],"wp:attachment":[{"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/media?parent=1935"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/categories?post=1935"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fastbitlab.com\/blog\/wp-json\/wp\/v2\/tags?post=1935"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}