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MPU demo LPC1768 link script problem

Posted by docsis on July 8, 2015

In file rtosdemordb1768Debug.ld, The privileged_data section simply set as bss:

privileged_data :
{
	_bss = .;
	*(privileged_data)
	/* Non kernel data is kept out of the first 256 bytes of SRAM. */
} > SRAM	

But in task.c, not all variable is zero initial value:

PRIVILEGED_DATA static volatile TickType_t xNextTaskUnblockTime		= portMAX_DELAY;

Not sure if this is an issue.


MPU demo LPC1768 link script problem

Posted by rtel on July 9, 2015

Thanks for pointing this out - it is an interesting one and I'm afraid I don't have an answer for how it worked however the head revision code no longer initialises this variable where it is declared, and instead initialises it immediately before the scheduler is started. The change was made explicitly to ensure the kernel itself had nothing outside the bss section.

You can see the head revision version here: https://sourceforge.net/p/freertos/code/HEAD/tree/trunk/FreeRTOS/Source/tasks.c#l250

Regards.


MPU demo LPC1768 link script problem

Posted by docsis on July 10, 2015

Thank you for your reply. Yes, this is the only privileged variable with no-zero initial value.

There are some other minor issues in link script, maybe also not issues: 1. If enable timer, PrivilegedDataRegionSize exceed 256. 2. If change flash start address to other value than zero, link fail. Have to change:

.text :
	{
		/* Non privileged code kept out of the first 16K or flash. */
		. = __privileged_functions_start__ + _Privileged_Functions_Region_Size;

to

.text :
	{
		/* Non privileged code kept out of the first 16K or flash. */
		. =  ORIGIN( FLASH ) + _Privileged_Functions_Region_Size;

In my environment, need change these to get right link result. 3. Also have to change this to put .bss after PrivilegedDataRegionSize.

. = ORIGIN( SRAM ) + _Privileged_Data_Region_Size;

.bss :
{
*(.bss*)
*(COMMON)
_ebss = .;
} > SRAM

to

.bss :
{
. = ORIGIN( SRAM ) + _Privileged_Data_Region_Size;
*(.bss*)
*(COMMON)
_ebss = .;
} > SRAM 


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