NVS Storage for ESP8266_NONOS_SDK

This is a port of the nvs_flash code of the ESP8266_RTOS_SDK

The nvs_flash provides a key value storage with wear leveling. A very good replacement for the EEPROM class that overwrites the same sector each time a single byte is changed and is limited to 4KB of data.

Documentation

https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/storage/nvs_flash.html

Partitions

2 Partitions are supported and need to be defined in the eagle.ld file. The default names are nvs and nvs2. The names can be changed in esp_partition.cpp. If NVS_PARTITIONS is set to 1, the second partition is not used

Second partition

The second partition is optional and NVS_PARTITIONS has to be set to 2. It needs to be initialized before use with nvs_flash_init_partition

Modifications

The code is only slightly modified, but relies on a replacement of the esp_partition_* functions since the NONOS_SDK does not have a readable runtime partition table. The partitions are grabbed from the eagle.ld linking file

Locking and multiple threads

Since the NONOS_SDK does not support multiple threads/tasks, interrupts must be disabled during all operations. If a call from an interrupt occurs, the code would lock up waiting for the unlock. This is usually not a problem unless init/deinit is frequently used. It blocks interrupts for several milliseconds depending on the size of the partition, while most other operations complete within a few dozen microseconds

If the nvs functions are not called from interrupts or timers, but only in the setup()/loop() function, locking is not required. If locking is disabled and the app requires nvs functions to be called from interrupts, nvs::Lock::isLocked() can be called to check if another operation is in progress

Encryption

Encryption is not supported

RAM usage

nvs_flash_init() allocates quite a lot RAM. The amount of memory required for initializing a partition varies and increases in time. To release about 1.5KB, use nvs_flash_deinit() if NVS is not required anymore. Same for nvs_flash_init_partition(). Initializing the partition again requires some time depending on th size (16-32ms for 32KB, depending on the flash speed) and blocks interrupts.

Changelog

0.0.3

• Added method Lock::isLocked() to determine if any nvs function is running (only available if interrupt locking is disabled)
• Option to disable interrupt locking (-D NVS_FLASH_NO_INTERRUPT_LOCK=1)

0.0.2

• Added example app

0.0.1

• Initial release