OVMS3-idf/examples/storage/nvs_rw_value/README.md

# Non-Volatile Storage (NVS) Read and Write Example

(See the README.md file in the upper level 'examples' directory for more information about examples.)

This example demonstrates how to read and write a single integer value using NVS.

In this example, value which is saved holds the number of ESP32 module restarts. Since it is written to NVS, the value is preserved between restarts.

Example also shows how to check if read / write operation was successful, or certain value is not initialized in NVS. Diagnostic is provided in plain text to help track program flow and capture any issues on the way.

Detailed functional description of NVS and API is provided in [documentation](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/storage/nvs_flash.html).

Check another example *storage/nvs_rw_blob*, which shows how to read and write variable length binary data (blob).

## How to use example

### Hardware required

This example does not require any special hardware, and can be run on any common development board.

### Configure the project

If using Make based build system, run `make menuconfig` and set serial port under Serial Flasher Options.

If using CMake based build system, no configuration is required.

### Build and flash

Build the project and flash it to the board, then run monitor tool to view serial output:

```
make -j4 flash monitor
```

Or, for CMake based build system (replace PORT with serial port name):

```
idf.py -p PORT flash monitor
```

(To exit the serial monitor, type ``Ctrl-]``.)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

## Example Output

First run:
```
Opening Non-Volatile Storage (NVS) handle... Done
Reading restart counter from NVS ... The value is not initialized yet!
Updating restart counter in NVS ... Done
Committing updates in NVS ... Done

Restarting in 10 seconds...
Restarting in 9 seconds...
Restarting in 8 seconds...
Restarting in 7 seconds...
Restarting in 6 seconds...
Restarting in 5 seconds...
Restarting in 4 seconds...
Restarting in 3 seconds...
Restarting in 2 seconds...
Restarting in 1 seconds...
Restarting in 0 seconds...
Restarting now.
```

Subsequent runs:

```
Opening Non-Volatile Storage (NVS) handle... Done
Reading restart counter from NVS ... Done
Restart counter = 1
Updating restart counter in NVS ... Done
Committing updates in NVS ... Done

Restarting in 10 seconds...
Restarting in 9 seconds...
Restarting in 8 seconds...
Restarting in 7 seconds...
Restarting in 6 seconds...
Restarting in 5 seconds...
Restarting in 4 seconds...
Restarting in 3 seconds...
Restarting in 2 seconds...
Restarting in 1 seconds...
Restarting in 0 seconds...
Restarting now.
```

Restart counter will increment on each run.

To reset the counter, erase the contents of flash memory using `make erase_flash` (or `idf.py erase_flash`, if using CMake build system), then upload the program again as described above.