A property storage system for storing non-volatile settings in MCU flash or OTP memory. The storage is highly memory and flash size optmized. It supports keys and variable data types like bits, numbers, strings, and blobs. There are pre-defined enums for storage keys (8-bit, 1-127, e.g. WIFI_SSID = 30) and custom keys (128-254). It supports intelligent re-writing of properties in flash memory to overcome limitations on limited flash write/erase cycles in MCUs, a kind of wear levelling done in the software via the “NVProperty” library.
NVProperty has a general API and supports multiple MCU types. Additional MCU models can be added by experienced programmers. The API is very simple to use and is identical on Arduino and Mbed OS, regardless of what kind of MCU is used. A property editor allows setting properties without any programming.
Example code:
NVProperty prop; const char *ssid = prop.GetProperty(prop.WIFI_SSID); int value = prop.GetProperty(prop.ADC_VREF);
Helmut Tschemernjak www.radioshuttle.de
- Mbed OS
- Arduino ESP32, D21
The NVProperty storage is usually at the end of the flash memory, e.g. 16 kB, assuming that the application does not reach the end of the flash area. Even NVProperty is optimized to distribute writes across its storage area, the number of writes should be limited to avoid flash erase cycle limitations.
Estimation for a 32kB NVProperty storage to show how many writes of a simple number (e.g. SetPropertyNET_IP_ADDR, T_32BIT, ...) are possible before reaching the end of life for the MCU flash chip:
- Microchoip D21: xxxx million writes
- STM32L4: xxxx million writes
- ESP32: (unkown because the ESP32 uses a different store backend)
Please note: A larger NVProperty storage area will allow better write distribution, larger storage values, e.g. strings, will reduce the number of writes. It is recommended to write properties only when it is needed, or collect changes and write these only from time to time.
Important note for D21 Arduino users: A custom version of “bossac” must be installed when using the NVProperty library, otherwise, properties cannot be saved. Download it from here. After unpacking the archive you will find the program for three different platforms:
The contents of the new bossac ZIP archive with its target installation directory
- bossac-linux64 (Linux) -> arduino15/packages/arduino/tools/bossac/1.7.0/
- bossac-macos (macOS) -> Library/Arduino15/packages/Arduino/tools/bossac/1.7.0/
- bossac.exe (Windows) -> AppData\Local\Arduino15\packages\arduino\tools\bossac\1.7.0\
Copy the appropriate binary for the platform you are using into the above directory and rename it to “bossac” (“bossac.exe” for the Windows platform is not renamed). For safety reasons it is recommended to backup the existing “bossac” program beforehand, e.g. to “bossac.save”.
- Add ESP32 efuse (OTP) memory write support (the ESP has only a few bytes, however a new ESP will have more )
The software is provided under the Apache 2.0 license. Contributions to this project are accepted under the same license.
This driver has initially been written by the RadioShuttle engineers (www.radioshuttle.de). Many thanks to everyone who helped bringing this project forward.
- Training video: "RadioShuttle - Non Volatile Settings (NVProperty)"
- Training slides: "RadioShuttle - Non Volatile Settings (NVProperty)"