CCS/MSP430FR5969: Understanding (HIGH) modifier with RAM memory section, use and applicability to other memory sections

The section .TI.noinit cannot be allocated to flash memory (FRAM or FRAM2).  Ordinary arrays, which are not subject to the NOINIT pragma or attribute, must go in memory which can be read and written, i.e. RAM.  NOINIT arrays have this same restriction, for the same reason.  The only difference between an ordinary array and a NOINIT array is whether the array is zero initialized before main starts.  An ordinary array is zero initialized, while a NOINIT array is not.  

Thanks and regards,

-George

The HIGH keyword is described in the Assembly Language Tool's User's Guide section 8.5.5.2.4 "Controlling Placement Using the HIGH Location Specifier"

[Edit - I can't get the forum to accept the URL for this link.  See http://downloads.ti.com/docs/esd/SLAU131/index.html and navigate from there --Archaeologist]

Thanks Archaeologist! Will do.

Hi George,

Thanks for the response. Please note the FR5969 is a Ferroelectric RAM based device, not flash. FRAM can be treated as fungible for the purposes of data and code storage. Moreover, the code snippet I included in the original post for the linker command file works as desired which suggests that your reply is not accurate.

Thanks again for the response.

Hi Katie. Thanks for the reply. Indeed I am storing a data array for long term sensor data storage (R/W). I had hoped to use both sections of FRAM to increase capacity but if necessary I can stick to the lower block. I do not want to have to include special directives to achieve basic operation as others will be using this sensor network and for maximum understandability I would like the code to be as clean as possible. With regard to using the PERSISTENT pragma rather than the NOINIT pragma, I found that PERSISTENT wants me to pre-initialize the data array and typing out the correct number of bytes (4000 plus) doesn't sound very appealing, however, if I am overlooking some simple tool to bypass this inconvenience I would be happy to consider it.

Kind regards

Bret Bronner said:

With regard to using the PERSISTENT pragma rather than the NOINIT pragma, I found that PERSISTENT wants me to pre-initialize the data array and typing out the correct number of bytes (4000 plus) doesn't sound very appealing

As per the C standard if a partial initializer is used the remaining elements will be implicitly initialized to zero.

E.g. in the following example of a 4000 element array for a MSP430FR5969 explicitly only initialized the first element and the large_array was then allocated in FRAM:

#include <msp430.h> 

#pragma PERSISTENT(large_array)
int large_array[4000] = {0};

/*
 * main.c
 */
int main(void) {
    WDTCTL = WDTPW | WDTHOLD;	// Stop watchdog timer
	
    large_array[0]++;

	return large_array[0];
}

Hi Bret,

Glad that we could help. As Chester mentioned, I think you should be able to just initialize it with = {0}; Please let us know if you run into more questions - you can post in the MSP low-power microcontroller forum too!

Regards,
Katie

Thanks Chester, I see that and will use it from now on. Cheers.