Merge pull request #1451 from UncleGrumpy/wifi_calibration

Utilize reserved `phy_init` partition on ESP32 for wifi calibration data

The `phy_init` partition has been reserved, but not used. By using the
`WIFI_STORAGE_FLASH` location the calibration data is preserved across restarts
in flash significantly improving connection times. The data stored using
`WIFI_STORAGE_RAM` is lost at boot up and needs to be recalibrated, the option
`WIFI_STORAGE_FLASH` will still load the data into ram from flash, but this is
much faster than performing a full calibration every boot, and should
significantly help battery powered devices that spend time in deep sleep and
only wake to collect and relay sensor data to the network.

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

Author: bettio

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - ESP32: improved sntp sync speed from a cold boot.
+- Utilize reserved `phy_init` partition on ESP32 to store wifi calibration for faster connections.
 
 ## [0.6.6] - Unreleased
 

src/platforms/esp32/components/avm_builtins/network_driver.c

@@ -690,7 +690,7 @@ static void start_network(Context *ctx, term pid, term ref, term config)
         port_send_reply(ctx, pid, ref, error);
         return;
     }
-    if (UNLIKELY((err = esp_wifi_set_storage(WIFI_STORAGE_RAM)) != ESP_OK)) {
+    if (UNLIKELY((err = esp_wifi_set_storage(WIFI_STORAGE_FLASH)) != ESP_OK)) {
         ESP_LOGE(TAG, "Failed to set ESP WiFi storage");
         term error = port_create_error_tuple(ctx, term_from_int(err));
         port_send_reply(ctx, pid, ref, error);