ESP32, NVS 이해하기

ESP32, NVS 이해하기

결론적으로 얘기하면 50% 정도만 이해하였다고 판단합니다.

0. 참고 사이트

• http://www.lucadentella.it/en/2017/06/03/esp32-19-nvs/
• https://github.com/lucadentella/esp32-tutorial/blob/master/13_nvs/
  
• https://esp-idf.readthedocs.io/en/latest/api-guides/partition-tables.html#
• https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/storage/nvs_flash.html#
• https://github.com/espressif/esp-idf/tree/020ade652d9b6b0b87b0bebe176a150cc4407749/components/nvs_flash
  

sglee@sglee-virtual-machine:~/esp/project/nvs_rw_value$ make partition_table
Partition table binary generated. Contents:
*******************************************************************************
# Espressif ESP32 Partition Table
# Name, Type, SubType, Offset, Size, Flags
nvs,data,nvs,0x9000,24K,
phy_init,data,phy,0xf000,4K,
factory,app,factory,0x10000,1M,
*******************************************************************************
Partition flashing command:
python /home/sglee/esp/esp-idf/components/esptool_py/esptool/esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 115200 --before default_reset --after hard_reset write_flash 0x8000 /home/sglee/esp/project/nvs_rw_value/build/partitions_singleapp.bin

로그를 분석하면

• offset 36KB : nvs,data,nvs,0x9000,24K,
• offset 60KB : phy_init,data,phy,0xf000,4K,
• offset 64KB: factory,app,factory,0x10000,1M,
  

sglee@sglee-virtual-machine:~/esp/project/nvs_rw_value$ make print_flash_cmd
--flash_mode dio --flash_freq 40m --flash_size detect 0x1000 bootloader/bootloader.bin 0x10000 nvs-rw-value.bin 0x8000 partitions_singleapp.bin

로그를 분석하면

• offset  4KB : 0x1000 bootloader/bootloader.bin
  
• offset 32KB : 0x8000 partitions_singleapp.bin
• offset 64KB : 0x10000 nvs-rw-value.bin
  
  

위 2개 로그를 토대로 4MB Flash Size를 쓴다면

4MB-----------------------

할당되지 않은 영역

1.64MB-----------------------

App 영역, 1MB, The bootloader will run this app by default

64KB (factory)-----------------------

phy 영역, 4KB, PHY init data

60KB (phy_init)-----------------------

nvs 영역, 24KB, NVS library partition

36KB (nvs)-----------------------

파티션 테이블, 가변적, 기본적인 partitions_singleapp.bin 크기는 3KB

32KB (partition_table)-----------------------

부트로더, ???KB

4KB (bootloader)-----------------------

???

0KB-----------------------

사용자가 사용할 수 있는 NVS 크기에 대해

홈페이지에서 설명하기를

String values are currently limited to 4000 bytes. This includes the null terminator. Blob values are limited to 508000 bytes or (97.6% of the partition size - 4000) bytes whichever is lower.

환산해 보면

3.9KB string
496KB blob

그리고 참고한 홈페이지 중에서 아래와 같이 언급하는데

그렇다면 NVS 파티션 24KB 영역 안에 사용자가 데이터가 들어가는 것으로 보여집니다.

storage1 = 4kb string

storage2 = 4kb string

...

If you use the default partition table (“Single factory app, no OTA”), you may notice that it contains a partition of type data and subtype nvs: The default size for that partition is 24Kbyte. Thanks to the NVS library, you can store custom data into that partition. Information is organized in key/value pairs; a label (= key) with a maximum length of 15 characters is assigned to each value: