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Handling flash double word 64-bit programming

e d
Associate II
Posted on June 26, 2017 at 21:21

Hi all,

I am working with the STM32L486 series and having a flash question. I need to save some NVM parameters to a 2K page in flash but the flash utils can only write double word at a time (64 bits). My NVM structure size will ebb and flow and would probably not align to a 64-bit boundary. How do I handle saving the structure gracefully in the code? I am thinking of padding some dummy bytes to meet the 64-bit boundary but it is a bit cumbersome. I used to do this feature in bytes easily when working with other processors capable of byte write, but this is a bit different. Any ideas?

Thanks,

ED

5 REPLIES 5
Posted on June 26, 2017 at 21:39

Can you just not use a struct, where you memcpy from FLASH to RAM, or read in-place, and then have a writing routine that commits the whole thing, rounded to an 8-byte boundary, from a RAM based buffer? Or malloc() the RAM buffer rounded up to the next 8-byte size, and access via a pointer.

I don't see a fault occurring unless the structure is pushed to the very top of RAM so not padding exists, but the stack is most likely there.

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Posted on June 26, 2017 at 22:21

Thanks Clive for the quick response, as always. I'd like to use a master RAM based NVM struct, which consists of a few sub structs, to do one shot memcpy as you mentioned. This contributes to the code clarity and efficiency, which are important to me.

Been thinking maybe I need to align all the sub structs to a 64-bit boundary. The unused bytes will be designated as spares to be replaced with actual parameters when a particular sub struct needs to expand. For example:

typedef struct NVM_STRUCT_ID

{

      uint16_t Param1;

      uint16_t

Param2

;

      uint16_t

Param3

;

     

uint16_t

Param4

;

     

uint16_t

Param5

;

     

uint16_t

spare1

;

     

uint16_t

spare2

;

     

uint16_t

spare3

;

} NVM_STRUCT_ID;

Of course the spares will be managed at a minimum to minimize foot print.

Will experiment a few methods as I go along.

misagh
Associate III
Posted on June 27, 2017 at 07:26

I usually prefer to pass the memory alignment to compiler by using unions. For example:

typedef struct MY_STRUCT
{
 uint16_t Param1;
 uint16_t Param2;
 uint16_t Param3;
} MY_STRUCT;
union{
 uint64_t u64;
 MY_STRUCT id;
}testunion;
uint64_t test64;
testunion.id.Param1 = 1;
testunion.id.Param2 = 2;
testunion.id.Param3 = 3;
test64 = testunion.u64; // converted NVM_STRUCT_ID to 64-bit variable�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?

Bests,

Misagh

e d
Associate II
Posted on June 27, 2017 at 19:30

Not sure how this is better since it looks like you need to allocate both 'testunion' (missing here?) and 'test64' to accomplish the same goal. Thanks anyway!

misagh
Associate III
Posted on June 28, 2017 at 07:40

Actually you do not need to test64. It just used to clarify that you can use the u64 variable as the converted struct.