Storing Data to flash memory

[Thomas]

Hi

I am using the Nordic NRF52840_dk with SDK 16.

I want to store data to flash memory with Ble and uart enabled. I am using a external UART peripheral to receive data which, I then parse and broadcast via a ble advertisement.

However, I wish to store this data locally along with a start time for the logging. The data is received once per second. I want this stored inside a log which, I can later send to a mobile application.

I therefore, presume I need to use the flashwrite example. And my code is based on RTT.

I have a value stored as a string that comes in from a UART. I need to store this string in flash memory. I am presuming having a String array is a poor way to do it. Given that I have a requirement for logging for a day meaning 86400 entries of data.

What I want to happen is a command to be sent from the android app to start a log. And then a command to stop it.

Also for transmitting the data that is stored on Nordic board(when working). I am not sure if the nordic board is capable of making a bluetooth connection and, if not will making a Gatt connection.

[Edvin]

Hello,

The Nordic Board is capable of Bluetooth Low Energy connections, just to answer your last question first.

So you want to store data that is sampled every second. While this is possible, as you say, it will require 86400 entries every day. How large are these samples?

As I see it, you have two options:

Either you can use the fstorage module, or you can use the FDS module (which uses fstorage module).

The difference between the two is that fstorage is more "down to metal",  where you need to decide to what address you want to write the data. Remember that you need to delete an entire flash page before you can write to the same address once more.

FDS will handle this for you, and always write to a free address. It operates with records that you can write, update and delete.

Try to read a bit about each of them. The advantage is that this will make sure of an even flash wear distribution, which will make your flash last longer. The disadvantage is that it has more overhead per record, so you may need to consider to gather up data for e.g. one minute, and save it all in one record.

Best regards,

Edvin

[Thomas]

Hi Edvin,

• Just to confirm then the nordic board is not capable of bluetooth connections then, meaning to transmit this data I will need a GATT connection?
• The data I want to store will be a string e.g 1,1100,1,1100,1,1000 something like that, this is my sensor data

Also then how do I print a single data log entry.

I presume something like this:

read file_id key_id. And it should return that data.

Edit:

From looking into it further I think the rec.id self increments and the file_id is passed into it.

How do i therefore, read it.

Also I need to merge this functionality of adding data to the flash storage with my project within the ble_peripheral folder. This however, uses UART with differently defined pins. I want the data to be added when new data comes in from this UART device not via the terminal.

Thanks,

Thomas

[Edvin]

If by "bluetooth" you mean "bluetooth classic", then no, the nRF52840 doesn't support it. But it does support Bluetooth Low Energy. (I guess you can call this a GATT Connection).

For the different fields, such as Record Key and File ID, see this page. 

Also, see the guide in the usage section on infocenter. This explains how to both write records, and to read records. Also, the Functionality section describes how to use record keys and File IDs.

[Thomas]

Cheers Edvin I'll look into those. Also would you therefore, have a recommendation about how to transmit data from the flash storage to my mobile application. As in what method should I use to do it?

[Edvin]

You need to use a BLE service + characteristic to transfer this data. The characteristic you need to use probably look a lot like the service that is implemented in the ble_app_uart example. This uses something called notifications to transfer data. In that example, it uses ble_nus_data_send() to send a text string, (or any other array of bytes). 

If you look into this example,  which you will find in SDK\examples\ble_peripheral\ble_app_uart, you can see that it usually calls ble_nus_data_send() inside the uart_event_handle(),  but you can send it at any other place in the code as well.

Also note that you can queue several packets using ble_nus_data_send(), until it returns NRF_ERROR_RESOURCES. Once that is returned, you must wait for the BLE_GATTS_EVT_HVN_TX_COMPLETE event (which you can add to ble_evt_handler() in main.c),  that means that one packet is ACKed by the connected device, and there is some space free in the softdevice queue, and you can start queuing new packets.

Best regards,

Edvin