Records on the use of easyflash v3.3

Open source address https://github.com/armink/EasyFlash
A post by an open source Author ：https://www.amobbs.com/thread-5624863-1-1.html

It has reached V4 了 , But here's the thing ST Of L4 Series MCU , Cannot write in reverse order , So it's still used V3 edition

The space is full occasionally when using , It's especially hard to reproduce , Just go through the source code

1. About wear balance
   Not a real wear balance , Just keep erasing and reading to a sector first , When this sector is broken , Translate another sector down , And as long as there is a write or erase failure in this sector, it will shift to the next sector ,V4 Implementation and V3 Totally different

2. About env Delete and reset ：
   /* remain ENV move forward */
   memcpy(del_env, del_env + del_env_length, remain_env_length);
   After deleting a key value pair , The cache data is uniformly shifted forward Then set the end address ;
   The cache area after the currently used address （env_cache） Size erase , Then write the shifted data from the current address
   save_cur_using_data_addr Is before writing 16 Byte lead data to the system area ;
   When deleting, there will be a space to save a set of data that will be saved every time you reset

3. About power failure protection ：
   Power failure protection is realized by software , It is not saved after detecting that the voltage of the single chip microcomputer is lower than a certain value , But the call ef_save_env_wt When , How many days after a write k Backup , Write the first few at a time k Really save , Back and forth twice , One is always the preservation of another , But this causes a waste of space

4. About get_env_user_used_size(void) The understanding of the ：
   static size_t get_env_user_used_size(void) {
   if (get_env_detail_end_addr() > get_cur_using_data_addr()) {
   return get_env_detail_end_addr() - get_cur_using_data_addr();
   } else {
   return 0;
   }
   }
   Why get the used size , Is to subtract the address in use from the end address , I can't understand the positive and reverse order ？
   Actually, it should be understood as get_env_detail_end_addr() Is the end address used , It always changes according to the size of the write , and get_cur_using_data_addr(); Are two fixed values , That is, if it weren't for the backup area , If it weren't for the real storage area

5. About env Space allocation ：
   Power down and wear balance mode , The distribution of the front and rear memory areas is consistent ：1 System area 、2 Data area
   Pay attention to the cache RAM size 、 Environment variable area 、 The size of the minimum erased sectors and their relationship

6. About the size of the persistent data area ：
   default_env_set_size： Always saved KEY-VALUE When resetting, write it to the last area of the cache
   Use set_env_detail_end_addr(get_env_detail_end_addr() + env_str_len); Set the stored content