Strange RAM usage on F28027

TobyM

Hi Folks

Im using the flash API to store some non-volatile data.

Im moving some sections around in RAM to allow me to store data that is to be written to flash. The data is a simple long integer (int32_t or dword) array, declared as follows:

#define PROFILE_SIZE 64

#pragma DATA_SECTION (profile0, 'FLASH_WRITE_Section');
int32_t profile0[PROFILE_SIZE] = {0};

My project .CMD file has the following for the relevant section:

SECTIONS
{
	FLASH_WRITE_Section	: > RAMM0	PAGE = 1
	/* Other sections here also for different RAM e.g. dataRAM or RAMM1... */
}

With PROFILE_SIZE set to 64 dwords this sees the expected size of FLASH_WRITE_Section of 128 words.

However if I add another array to the same section with a size of just 1, the section size balloons up to 192 words, making the memory allocation fail!! (RAMM0 also contains 768 words of stack)

Where are the extra 62 words coming from?

Thanks

over 11 years ago

0 TobyM over 11 years ago

Genius 5200 points

Hmm after a little more thinking I guess this is allocation of RAM happening in blocks of 64 dwords? Seems logical reason for the change as the memory size then does not increase again until I change the second array size above 64 dwords.

However if I attempt to do this (i.e. change the second array to 64 dwords), memory allocation fails for the section being too large even if I spread the section over RAMM0 and RAMM1, both of which have room for at least one of the two arrays.

Surely if I have:

	FLASH_WRITE_Section   : >> RAMM0 | RAMM1   PAGE = 1

Then profile0 @ 64 dwords should fit into RAMM0 as it has 88 dwords of free space and profile1 @ 64 dwords should fit into RAMM1 as it has 118 dwords of free space... yet memory allocation fails for 11 dwords of the section... Whay is this???

Thanks

0 Lori Heustess over 11 years ago in reply to TobyM

TI__Guru* 92080 points

Toby - I believe the compiler data page blocking is what you are running into. It allows the compiler to efficiently access data by stetting the data page once.

Here is a description:

http://processors.wiki.ti.com/index.php/C28x_Compiler_-_Understanding_Linking#Q:_The_linker_says_.22placement_fails_for_object.22_but_the_available_memory_is_larger_than_the_section

Regards

Lori

0 TobyM over 11 years ago in reply to Lori Heustess

Genius 5200 points

Hi Lori, that definitely sounds like it!

Maybe I'll make each struct separately and just keep an array of pointers to them.

Thanks.

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Strange RAM usage on F28027