topic Re: why SHELL_Main() doesn't work in xTaskCreate in FreeRTOS? in MCUXpresso SDK

why SHELL_Main() doesn't work in xTaskCreate in FreeRTOS?

jren68 — Fri, 26 Oct 2018 17:33:09 GMT

I am looking at the shell demo for LPC54018. In the demo the SHELL_Main() function from fsl_shell.c was used, and it works when used this way

script in Main.c

SHELL_Main(&context);

console

SHELL (build: Oct 26 2018)
Copyright (c) 2017 NXP Semiconductor
SHELL>> start loop, context = 0x2fec0

Now if I wrap the SHELL_Main in xTaskCreate, and then run vTaskStartScheduler(). It doesn't work despite the pointer was successfully passed in

script in Main.c

xTaskCreate(
SHELL_Main,
"shell",
1024,
&context,
1,
NULL);
vTaskStartScheduler();

console

SHELL (build: Oct 26 2018)
Copyright (c) 2017 NXP Semiconductor
SHELL>> start loop, user_context = 0x2fec0
context->exit

This is the starting section of the source code, bolded are the printf I added to help debug. As can be seen the context passed into the function is the same, however, when wrapped by xTaskCreate, if (context->exit) was triggered.

int32_t SHELL_Main(p_shell_context_t context)
{
printf("entered shell_main\n");
uint8_t ch;
int32_t i;
if (!context)
{
return -1;
}
context->exit = false;
context->printf_data_func("\r\nSHELL (build: %s)\r\n", __DATE__);
context->printf_data_func("Copyright (c) 2017 NXP Semiconductor\r\n");
context->printf_data_func(context->prompt);

while (1)
{
printf("start loop, context = %p\n", context);
if (context->exit)
{
printf("context->exit");
break;
}
....

Why the same pointer will trigger different conditions when directly called and when wrapped in Tasks?

Re: why SHELL_Main() doesn't work in xTaskCreate in FreeRTOS?

jren68 — Fri, 26 Oct 2018 19:51:36 GMT

For some reason, the context->exit is changed from 0 to a value after the vTaskStartScheduler()

Re: why SHELL_Main() doesn't work in xTaskCreate in FreeRTOS?

danielchen — Mon, 29 Oct 2018 08:10:21 GMT

Hi Jenny:

Please check whether there is a stack overflow, increase the stack size to a bigger value.

Regards

Daniel

Re: why SHELL_Main() doesn't work in xTaskCreate in FreeRTOS?

jren68 — Mon, 29 Oct 2018 18:14:55 GMT

Hi Daniel,

Thanks for the reply. I have suspected stackoverflow but soon found updating the stack size didn't help either.

I later found the problem is that I have initialized the context in main, outside of the stack of the createTask function. I should have initialized the context within the xTaskCreate() function such that this context pointer is not accidently overwritten by something else

Previously I was

int main(void) {
  shell_context_struct user_context; // the user_context is not in the stack of the created task
  SHELL_Init(&user_context, ...);
  xTaskCreate(
      SHELL_Main,
      "shell",
      512,
      &user_context,
      1,
      NULL);
}

I should have

int main(void){
xTaskCreate(
  start_shell,
  "shell",
  512,
  NULL,
  1,
  NULL);
}
void start_shell(void * p ) {
  shell_context_struct user_context;
  SHELL_Init(&user_context,....);
  SHELL_Main(&user_context);
}

Re: why SHELL_Main() doesn't work in xTaskCreate in FreeRTOS?

danielchen — Tue, 30 Oct 2018 01:42:34 GMT

Ah yes, thank you for your sharing!

Regards

Daniel

Re: why SHELL_Main() doesn't work in xTaskCreate in FreeRTOS?

jren68 — Wed, 31 Oct 2018 23:01:27 GMT

though i'd say don't use the SHELL_Main()

This IO function uses MUTEX_SEMAPHORE_BLOCKING(), which blocks the rest of the tasks regardless of their priority (facepalm)