pstorage blocks and pages

[talha]

Hi guys, I am trying to use pstorage to store a temperature data inside the ROM. I have to use it as efficiently as possible so that 20.000 erase cycles should be enough for my application. I am wondering a couple of things. First, how does pstorage module give the numbers to its blocks? I mean logically pstorage should register the blocks starting from 0 to whatever the number of blocks in an increasing order, putting each block of data consecutively so is that what it is doing?

Let's say I have initialized my pstorage as the following:

static void m_pstorage_init()
{
uint32_t err_code;         
pstorage_module_param_t p_example_param;    

p_example_param.block_size  = 0x4; // recommended to be >= 4 byte
p_example_param.block_count = 1024;
p_example_param.cb          = m_pstorage_handler;

err_code = pstorage_init();
APP_ERROR_CHECK(err_code);

err_code = pstorage_register (&p_example_param, &m_pstorage);
APP_ERROR_CHECK(err_code);
}

Since my block_size = 4 bytes and number of blocks is 1024, I need 4 pages. Is it safe to assume that blocks 0-255 are in the same page and 256-511 are in the same page and so on. I am not concerned if the pages that are used are consecutively stored (are they though? :) ), I am just asking is it safe to assume that block 256 will not be affected when I call pstorage_clear() for the block 212?

Secondly, when I call pstorage_clear() for one block of data, it erases the whole page, but does it re-write other blocks that were on the same page back to their previous positions? If so, how can I avoid doing that.

Lastly, is there another module that you can offer to perform this action easily?

Sorry for my english, if there is any parts I was unable to explain please ask.

Thanks in advance,

Talha

[Stefan Birnir Sverrisson]

Hi Talha

For pstorage, data is statically stored, meaning that whenever you write a specific block, that block will always be located in the same physical memory address in flash. There is therefore no wear leveling present for pstorage. Flash data storage (fds) library however implements wear leveling of flash, which I recommend to use instead of pstorage if flash wearing is of concern. An fds example is presented here. fds is still in experimental state, but I expect it sooner than later to be out of experimental state, as it contains popular features that pstorage does not provide. Also, pstorage module has also been removed from nRF5 SDK 12, as all example applications now use fstorage instead, which has similar functionality as pstorage. FDS is an abstraction layer on top of fstorage with file+record abstraction.

For pstorage, there is an example available here. How pstorage constructs data in memory is described on this thread. pstorage_erase function erases a whole page without restoring any data on the erased page. With pstorage_update however, you can erase a block and the rest of the page will be restored. See this thread in order to realize what pstorage_update function actually performs.