FDS writes while performing garbage collection.

[bart]

I'm testing this with SDK 15.2 on an NRF52832, with SD132.

The documentation says: "When the space is exhausted, write requests return the error FDS_ERR_NO_SPACE_IN_FLASH, and you must run garbage collection and wait for completion before repeating the call to the write function."

But if i call fds_record_update(), immeditaly after calling fds_gc(), it will return FDS_ERR_SUCCESS. Has this behaviour changed, while documention was not? Is it safe to write before GC is done?

[Jared]

Hi,

The reason that you should wait for the asynchronous function to return is because it guarantees that the garbage collection has released the memory. A program that doesn't wait for the function to return could result in unexpected behavior. 

Best regards

Jared

[bart]

Right, so shouldn't fds_record_write() return FDS_ERR_BUSY? I only have 1 FDS user, but when you have multiple, the other users don't even know GC started.

[Jared]

Hi, 

No, FDS_ERR_BUSY is not returned by fds_record_write(), but is returned by record_write_data(). The latter is an internally function used by the module which is not meant to be used directly by the application. The documentation for fds_record_write() specifies the return types as follows:

Return values

FDS_SUCCESS	If the operation was queued successfully.
FDS_ERR_NOT_INITIALIZED	If the module is not initialized.
FDS_ERR_NULL_ARG	If p_record is NULL.
FDS_ERR_INVALID_ARG	If the file ID or the record key is invalid.
FDS_ERR_UNALIGNED_ADDR	If the record data is not aligned to a 4 byte boundary.
FDS_ERR_RECORD_TOO_LARGE	If the record data exceeds the maximum length.
FDS_ERR_NO_SPACE_IN_QUEUES	If the operation queue is full or there are more record chunks than can be buffered.
FDS_ERR_NO_SPACE_IN_FLASH	If there is not enough free space in flash to store the record.

Note: that the return of FDS_SUCCESS does not mean that the write operation is done, but that the operation has been staged. 

Best regards

Jared

[bart]

Indeed, it returns success, while it should not, since you have to wait for GC to be done. So my suggestion is that it should return FDS_ERR_BUSY when GC is running.

[Jared]

I understand. I'll forward your suggestion to the developing team.