titi/ESP32_OSC_IMU: Using M5 stack gray hardware @ d5234346ba7cdd350fcb1e664b41bb29f89fb109

Saved credentials in the flash

AutoConnect stores the credentials of the established WiFi connection in the flash memory of the ESP8266/ESP32 module and equips the class to access the credentials from the sketch. You can read, write, or erase the credentials using this class individually. It's the AutoConnectCredential, which provides the way of access to the credentials stored in flash.[^1]

[^1]:An example using AutoConnectCredential is provided as an example of a library sketch to delete saved credentials.

Credentials storage location

The location where AutoConnect saves credentials depends on the module type and the AutoConnect library version, also arduino-esp32 core version. In either case, the location is flash memory, but EEPROM and Preferences (in the nvs[^2]) are used depending on the library versions.

AutoConnect	Arduino core for ESP8266	Arduino core for ESP32
AutoConnect	Arduino core for ESP8266	1.0.2 earlier	1.0.3 later
v0.9.12 earlier	EEPROM	EEPROM (partition)	Not supported
v1.0.0 later	EEPROM	Preferences (nvs) (Can be used EEPROM with turning off AUTOCONNECT_USE_PREFERENCES macro)	Preferences (nvs)

However, sketches do not need to know where to store credentials using the commonly accessible AutoConnectCredential API.

If you are using an Arduino core for ESP32 1.0.2 earlier and need to use credentials in EEPROM for backward compatibility, turns off the AUTOCONNECT_USE_PREFERENCES[^3] macro definition in AutoConnectCredentials.h file. AutoConnect behaves assuming that credentials are stored in EEPROM if AUTOCONNECT_USE_PREFERENCES is not defined.

[^2]:The namespace for Preferences used by AutoConnect is AC_CREDT. [^3]:Available only for AutoConnect v1.0.0 and later.

AutoConnectCredential

Include header

#include <AutoConnectCredential.h>

Constructors

AutoConnectCredential();

AutoConnectCredential default constructor. The default offset value is 0. In ESP8266 or ESP32 with arduino core 1.0.2 earlier, if the offset value is 0, the credential area starts from the top of the EEPROM. If you use this area in a user sketch, AutoConnect may overwrite that data.

AutoConnectCredential(uint16_t offset);

Parameter: offsetSpecies offset from the top of the EEPROM for the credential area together. The offset value is from 0 to the flash sector size. This parameter is ignored for AutoConnect v1.0.0 or later with arduino-esp32 core 1.0.3 or later.

Public member functions

entries

uint8_t entries(void)

Returns number of entries as contained credentials.

<dt>**Return value**</dt>
<dd>Number of entries as contained credentials.</dd></dl>

load

int8_t load(const char* ssid, station_config_t* config)

Load a credential entry and store to config.

<dt>**Parameters**</dt>
<dd><span class="apidef">ssid</span><span class="apidesc">SSID to be loaded.</span></dd>
<dd><span class="apidef">config</span><span class="apidesc">station_config_t</span></dd>
<dt>**Return value**</dt>
<dd>Save the specified SSID's credential entry to `station_config_t` pointed to by the parameter as **config**. -1 is returned if the SSID is not saved.</dd></dl>

load

bool load(int8_t entry, station_config_t* config)

Load a credential entry and store to config.

<dt>**Parameters**</dt>
<dd><span class="apidef">entry</span><span class="apidesc">Specifies the index number based 0 to be loaded.</span></dd>
<dd><span class="apidef">config</span><span class="apidesc">station_config_t</span></dd>
<dt>**Return value**</dt>
<dd>Save the specified credential entry to `station_config_t` pointed to by the parameter as **config**. -1 is returned if specified number is not saved.</dd></dl>

save

bool save(const station_config_t* config)

Save a credential entry.

<dt>**Parameter**</dt>
<dd><span class="apidef">config</span><span class="apidesc">station_config_t to be saved.</span></dd>
<dt>**Return value**</dt>
<dd><span class="apidef">true</span><span class="apidesc">Successfully saved.</span></dd>
<dd><span class="apidef">false</span><span class="apidesc">Failed to save.</span></dd></dl>

del

bool del(const char* ssid)

Delete a credential the specified SSID.

<dt>**Parameter**</dt>
<dd><span class="apidef">ssid</span><span class="apidesc">SSID to be deleted.</span></dd>
<dt>**Return value**</dt>
<dd><span class="apidef">true</span><span class="apidesc">Successfully deleted.</span></dd>
<dd><span class="apidef">false</span><span class="apidesc">Failed to delete.</span></dd></dl>

!!! example "Clear saved credentials"

There is no particular API for batch clearing of all credential data stored by AutoConnect. It is necessary to prepare a sketch function that combines several AutoConnectCredential APIs  to erase all saved credentials.
The following function is an implementation example, and you can use it to achieve batch clearing.

```cpp
void deleteAllCredentials(void) {
  AutoConnectCredential credential;
  station_config_t config;
  uint8_t ent = credential.entries();

  while (ent--) {
    credential.load(0, &config);
    credential.del((const char*)&config.ssid[0]);
  }
}
```

The data structures

station_config_t

The saved credential structure is defined as station_config_t in the AcutoConnectCredential header file.

typedef struct {
  uint8_t ssid[32];
  uint8_t password[64];
  uint8_t bssid[6];
  uint8_t dhcp;   /**< 0:DHCP, 1:Static IP */
  union _config {
    uint32_t  addr[5];
    struct _sta {
      uint32_t ip;
      uint32_t gateway;
      uint32_t netmask;
      uint32_t dns1;
      uint32_t dns2;
    } sta;
  } config;
} station_config_t;

!!! note "The byte size of station_config_t in program memory and stored credentials is different"

There is a gap byte for boundary alignment between the `dhcp` member and the static IP members of the above `station_config_t`. Its gap byte will be removed with saved credentials on the flash.

The credential entry

A data structure of the credential saving area in EEPROM as the below. [^4]

[^4]: There may be 0xff as an invalid data in the credential saving area. The 0xff area would be reused.

!!! note "AutoConnectCredential has changed"

It was lost AutoConnectCredential backward compatibility. Credentials saved by AutoConnect v1.0.3 (or earlier) will not work properly with AutoConnect v1.1.0. You need to erase the flash of the ESP module using the esptool before the sketch uploading.
```powershell
esptool -c esp8266 (or esp32) -p [COM_PORT] erase_flash
```

byte offset	Length	Value
0	8	AC_CREDT
8	1	Number of contained entries (uint8_t)
9	2	Container size, excluding size of AC_CREDT and size of the number of entries(width for uint16_t type).
11	variable	SSID terminated by 0x00. Max length is 32 bytes.
variable	variable	Password plain text terminated by 0x00. Max length is 64 bytes.
variable	6	BSSID
variable	1	Flag for DHCP or Static IP (0:DHCP, 1:Static IP)
	The following IP address entries are stored only for static IPs.
variable(1)	4	Station IP address (uint32_t)
variable(5)	4	Gateway address (uint32_t)
variable(9)	4	Netmask (uint32_t)
variable(13)	4	Primary DNS address (uint32_t)
variable(17)	4	Secondary DNS address (uint32_t)
variable	variable	Contained the next entries. (Continuation SSID+Password+BSSID+DHCP flag+Static IPs(if exists))
variable	1	0x00. End of container.

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Saved credentials in the flash

Credentials storage location

AutoConnectCredential

Include header

Constructors

Public member functions

entries

load

load

save

del

The data structures

station_config_t

The credential entry

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