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]

What does p_data look like in the flash_storage_read_data() function right before you copy it over to the m_sensor_cfg?

Try to set a breakpoint and watch that data.

Did you wait for the write complete event before you read it?

[Thomas]

When I place a breakpoint on  memcpy(&m_sensor_cfg, config.p_data, sizeof(configuration_t));

I run over it and, it goes to NRF_BREAKPOINT_COND.

So I am not sure how to test it.

I presume I am writing the information incorrectly and reading it incorrectly.

Given the aforementioned line of code should print out "sensor" as this is what I believe I write to the configuration file.

However, I don't want to read the configuration file. I want to read the latest data.

But, I can't find an example of where to do that in the sdk example code. Or the documentation.

[Edvin]

If you set a breakpoint and then resume,  the softdevice will assert. That is fine, you just need to reset.

Just set a breakpoint at the line memcpy, and right click config.p_data and click "add to watch". What this button is called depends on your IDE.

If you are not able to see the content of the pointer, then you need to disable optimization in your project.If you are not sure how to do that, let me know what IDE you are using.

[Thomas]

Im using segger.

On the line:

  rc = fds_record_open(&desc, &config);//Read data

How do I read the last entry. I presume the config that is in the flash is the default dummy one.

So my question is what is desc? Is this the specfic instance that is read?

Because I want to call a function that I can read the last record from. I will later need to read all the data. But I am thinking of doing this in a for loop from the first entry to the last.

[Edvin]

Hello,

Desc is the descriptor which is used to find and store values in records. config is the variable (fds_flash_record_t) that holds the actual flash data. You can check the definitions of these variable types in fds.h for an explanation.

Have you seen the usage section on infocenter? It contains some pointers on how to use the records. So check out the variable types and this guide.

Best regards,

Edvin