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cflashmemorystructmsp430

MSP430 Ram Overflow

The MSP430G2553 only has 512 Bytes of RAM but 16KB of FLASH memory. On this microcontroller, all static/global variables are assigned in RAM under .bss section. All local variables are assigned in RAM under .stack section. All dynamically allocated memory variables (malloc) are assigned in RAM under .sysmem section.

I have a need for this MSP430 to keep track of connected devices via wifi. I have a struct as such:

struct dev
{
    char type[20];
    char ipAddress[13];
    char name[20];
    char status[1];
};

This struct takes up 54 bytes of memory for each device. I am planning on having 20+ devices connected that this MSP430 and need to have 20 of these structs. 20 x 54 bytes = 1080 bytes. This is obviously too big for the 512 bytes of ram.

Is there any way to write these structs into FLASH since I have 16KB of memory to use? My understanding of FLASH is variables that are only read-only. These structs will obviously be getting assigned so it is read-write and I am not sure if it is possible.

I don't quite understand why TI would make a device which has 16 KB FLASH and only 512 Bytes of RAM, when all variables requiring read-write operations are stored in RAM. Seems like it is a waste of space.

I have tried to change these sections .bss/.stack/.sysmem to FLASH in the linker file and the MSP430 will not run like this. I have also tried to change the size of the RAM and in linker file and change the memory locations adding another 512 Bytes, but it will not run like this either.

Do I have any options here?

Solution

  • Yes, you can write data into the flash memory. The only problem arises when you want to change the data. You can only erase sectors, which have a size of 512 bytes. So you could take two flash sectors from the flash and store data for 10 devices in each sector. The flash can be read like RAM though, so you don't need some kind of swapping code, you just address each device entry with a pointer. The last problem is that flash memory has a limit of erase cycles, here around 10000 cycles. So you might also have to write code to distribute the data to different sectors over time, depending on the amount of expected changes and the desired service durability.