The same code getting FDS_ERR_UNALIGNED_ADDR in Release mode but not in Debug mode

Question

Hello, 
 
 I am using nRF52832, SDK_15.3.0, S132 SoftDevice and Segger for flashing the image. I am using ‘ble_app_blinky’. 
 I am using FDS module to write into Flash. I am observing strange behavior. I have gone through fds example. 
 
 Below is my structure. Initially either in Release or Debug mode I did not face any problem. Suddenly I started getting FDS_ERR_UNALIGNED_ADDR for same code base (I added few code for other functionality). 
 
 /* A record containing Datalog state data. */
static fds_record_t const DtStateRecord =
{
 .file_id = FILE_ID,
 .key = RECORD_KEY_2,
 .data.p_data = &eDataLogRecordingState,
 /* The length of a record is always expressed in 4-byte units (words). */
 .data.length_words = (sizeof(eDataLogRecordingState) + 3) / sizeof(uint32_t),
}; 
 
 My queries are 
 1) Whether "eDataLogRecordingState" in above structure should be word aligned. 
 
 2) In fds example only 'length_words' variable is make sure multiple of 4. But no where data.p_data is word aligned. 
 
 3) In "Debug" mode eDataLogRecordingState is word aligned (0x0000000020002e28). Where as in "Release" mode eDataLogRecordingState is not word aligned (0x0000000020002dc9). Will this cause FDS_ERR_UNALIGNED_ADDR error. 
 
 4) To make sure always word aligned then whether below way is fine. If yes, better modify FDS example so that it will be easy for new developers. In that case, irrespective of aligned or not aligned, __ALIGN(4) to be kept for all FDS variables so that FDS variables will always be word aligned. 
 
 __ALIGN(4) DataLogRecordingStates_t eDataLogRecordingState = 0;

Thanks & Regards 
 Vishnu Beema

Håkon Alseth · Accepted Answer

Hi,

1) Whether "eDataLogRecordingState" in above structure should be word aligned. 
 Yes, that must be word aligned for fds to accept it. 
 
 2) In fds example only 'length_words' variable is make sure multiple of 4. But no where data.p_data is word aligned. 3) In "Debug" mode eDataLogRecordingState is word aligned (0x0000000020002e28). Where as in "Release" mode eDataLogRecordingState is not word aligned (0x0000000020002dc9). Will this cause FDS_ERR_UNALIGNED_ADDR error. 
 This will give a return error code, as per the definition of fds_record_write: 
 * Record data can consist of multiple chunks. The data must be aligned to a 4 byte boundary, and
 * because it is not buffered internally, it must be kept in memory until the callback for the
 * operation has been received. The length of the data must not exceed @ref FDS_VIRTUAL_PAGE_SIZE
 * words minus 14 bytes. 
 
 4) To make sure always word aligned then whether below way is fine. If yes, better modify FDS example so that it will be easy for new developers. In that case, irrespective of aligned or not aligned, __ALIGN(4) to be kept for all FDS variables so that FDS variables will always be word aligned. 
 I will report this as a feature request internally to the developers. 
 
 Kind regards, 
 Håkon

The same code getting FDS_ERR_UNALIGNED_ADDR in Release mode but not in Debug mode

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