Hi DevZone !
I am using the nRF52840 for development and after some tests one of the chips could not access its memory flash in the function fds_init() in the library fds.c. I debugged it with Ozone and I saw the error FDS_ERR_NO_PAGES popping up. Can I repair the flash in some way ? Any suggestion on why it happened ?
Thank you !
Joel V.
Hi,
Sorry for the poor explanation. Let me try again 
The FDS module is an asynchronous module which means that operations doesn't complete when the function call is returned, a return with nRF_SUCESS only means that the operation was added successfully to the queue. You have to wait for the callback handler to be called with the appropriate event to be sure that the operation has completed. Updating or deleting a record does not free up the physical memory. It only invalidates the record. The physical memory is only freed once the garbage collector is called and frees up all of the invalidated memory. You therefore have to call the garbage collector before the memory is full.
Assuming these two parts are the only FDS operations that you normally do in your application:
1. Here you initialize the FDS module, run the garbage collector and read the record. Which is fine. You might want to wait for the garbage collector operation to complete first, but I don't think that it's crucial.
rc = fds_init();
rc = fds_gc();
APP_ERROR_CHECK(rc);
fds_record_desc_t desc = {0};
fds_find_token_t tok = {0};
rc = fds_record_find(CONFIG_FILE, CONFIG_REC_KEY, &desc, &tok);
if (rc == NRF_SUCCESS){
//rc = fds_record_delete(&desc);
//APP_ERROR_CHECK(rc);
fds_flash_record_t fds_config = {0};
//Open the record and read its contents.
rc = fds_record_open(&desc, &fds_config);
APP_ERROR_CHECK(rc);
//Copy the configuration from flash into config.
memcpy(&config, fds_config.p_data, sizeof(config_t));
//Close the record when done reading.
rc = fds_record_close(&desc);
APP_ERROR_CHECK(rc);
2. Here you write a new record to the FDS. If it fails you run the garbage collector.
fds_record_t config_record ={
.file_id = CONFIG_FILE,
.key = CONFIG_REC_KEY,
.data.p_data = &config,
/* The length of a record is always expressed in 4-byte units (words). */
.data.length_words = (sizeof(config_t)+3)/sizeof(uint32_t),
};
rc = fds_record_write(&desc, &config_record);
if(rc != NRF_SUCCESS){
rc = fds_gc();
APP_ERROR_CHECK(rc);
config_init(mesh_config);
}
APP_ERROR_CHECK(rc);
Re-doing step 1 and 2 multiple times for example by reset the application will eventually fill up the flash. This is because you never invalidate a record by either deleting or updating a record, which means that the garbage collector will not do anything. Reset the application will effectively write a new record with the same record and same file ID to the FDS without deleting the old one, since FDS does not require uniqueness for file ID nor file record key. I would suggest that you try to use the fds_record_update() instead, which will invalidate the old record when you write a new record with the same record ID and record key. The garbage collector will then free up the memory when it's called. Note that you need to wait for the operation to be completed as stated earlier.
best regards
Jared