Bootloader: retained memory can now be kept after reboot when custom data enabled

User's custom data are not taken into account during the CRC calculation anymore.
Which means taht the retained mem structure is not systematically erased
on each reboot anymore.

components/bootloader/Kconfig.projbuild

@@ -385,7 +385,6 @@ menu "Bootloader config"
 
     config BOOTLOADER_CUSTOM_RESERVE_RTC_SIZE
         hex "Size in bytes for custom purposes"
-        range 0 0x10
         default 0
         depends on BOOTLOADER_CUSTOM_RESERVE_RTC
         help

components/bootloader_support/include/esp_image_format.h

@@ -53,8 +53,14 @@ typedef struct {
     uint32_t crc;                   /*!< Check sum crc32 */
 } rtc_retain_mem_t;
 
+
+_Static_assert(offsetof(rtc_retain_mem_t, crc) == sizeof(rtc_retain_mem_t) - sizeof(uint32_t), "CRC field must be the last field of rtc_retain_mem_t structure");
+
 #ifdef CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC
 _Static_assert(CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC_SIZE % 4 == 0, "CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC_SIZE must be a multiple of 4 bytes");
+/* The custom field must be the penultimate field */
+_Static_assert(offsetof(rtc_retain_mem_t, custom) == sizeof(rtc_retain_mem_t) - sizeof(uint32_t) - CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC_SIZE,
+               "custom field in rtc_retain_mem_t structure must be the field before the CRC one");
 #endif
 
 #if defined(CONFIG_BOOTLOADER_SKIP_VALIDATE_IN_DEEP_SLEEP) || defined(CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC)

components/bootloader_support/src/bootloader_common_loader.c

@@ -139,6 +139,8 @@ esp_err_t bootloader_common_get_partition_description(const esp_partition_pos_t
 
 #define RTC_RETAIN_MEM_ADDR (SOC_RTC_DRAM_HIGH - sizeof(rtc_retain_mem_t))
 
+_Static_assert(RTC_RETAIN_MEM_ADDR >= SOC_RTC_DRAM_LOW, "rtc_retain_mem_t structure size is bigger than the RTC memory size. Consider reducing RTC reserved memory size.");
+
 rtc_retain_mem_t *const rtc_retain_mem = (rtc_retain_mem_t *)RTC_RETAIN_MEM_ADDR;
 
 #ifndef BOOTLOADER_BUILD
@@ -151,14 +153,25 @@ rtc_retain_mem_t *const rtc_retain_mem = (rtc_retain_mem_t *)RTC_RETAIN_MEM_ADDR
 SOC_RESERVE_MEMORY_REGION(RTC_RETAIN_MEM_ADDR, RTC_RETAIN_MEM_ADDR + sizeof(rtc_retain_mem_t), rtc_retain_mem);
 #endif
 
+static uint32_t rtc_retain_mem_size(void) {
+#ifdef CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC
+    /* A custom memory has been reserved by the user, do not consider this memory into CRC calculation as it may change without
+     * the have the user updating the CRC. Return the offset of the custom field, which is equivalent to size of the structure
+     * minus the size of everything after (including) `custom` */
+    return offsetof(rtc_retain_mem_t, custom);
+#else
+    return sizeof(rtc_retain_mem_t) - sizeof(rtc_retain_mem->crc);
+#endif
+}
+
 static bool check_rtc_retain_mem(void)
 {
-    return esp_rom_crc32_le(UINT32_MAX, (uint8_t*)rtc_retain_mem, sizeof(rtc_retain_mem_t) - sizeof(rtc_retain_mem->crc)) == rtc_retain_mem->crc && rtc_retain_mem->crc != UINT32_MAX;
+    return esp_rom_crc32_le(UINT32_MAX, (uint8_t*)rtc_retain_mem, rtc_retain_mem_size()) == rtc_retain_mem->crc && rtc_retain_mem->crc != UINT32_MAX;
 }
 
 static void update_rtc_retain_mem_crc(void)
 {
-    rtc_retain_mem->crc = esp_rom_crc32_le(UINT32_MAX, (uint8_t*)rtc_retain_mem, sizeof(rtc_retain_mem_t) - sizeof(rtc_retain_mem->crc));
+    rtc_retain_mem->crc = esp_rom_crc32_le(UINT32_MAX, (uint8_t*)rtc_retain_mem, rtc_retain_mem_size());
 }
 
 void bootloader_common_reset_rtc_retain_mem(void)

components/bootloader_support/test_apps/rtc_custom_section/CMakeLists.txt

@@ -0,0 +1,6 @@
+# The following lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(test_rtc_custom_section)

components/bootloader_support/test_apps/rtc_custom_section/README.md

@@ -0,0 +1,2 @@
+| Supported Targets | ESP32 | ESP32-C3 | ESP32-S2 | ESP32-S3 |
+| ----------------- | ----- | -------- | -------- | -------- |

components/bootloader_support/test_apps/rtc_custom_section/main/CMakeLists.txt

@@ -0,0 +1,2 @@
+idf_component_register(SRCS "test_main.c"
+                       INCLUDE_DIRS ".")

components/bootloader_support/test_apps/rtc_custom_section/main/test_main.c

@@ -0,0 +1,31 @@
+/*
+ * SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "bootloader_common.h"
+#include <stdio.h>
+#include "sdkconfig.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+
+#define TEST_MAGIC_VALUE 0x42987561
+
+extern rtc_retain_mem_t* bootloader_common_get_rtc_retain_mem(void);
+
+void app_main(void) {
+    rtc_retain_mem_t* mem = bootloader_common_get_rtc_retain_mem();
+    uint32_t* _rtc_vars = (uint32_t*) mem->custom;
+
+    if (_rtc_vars[0] != TEST_MAGIC_VALUE) {
+        /* On the first boot, set the data inside the array */
+        _rtc_vars[0] = TEST_MAGIC_VALUE;
+    } else {
+        /* Second boot, the data was saved saved, success */
+        printf("SUCCESS: data were saved across reboot\n");
+        vTaskDelay(10000 / portTICK_PERIOD_MS);
+    }
+
+    esp_restart();
+}

components/bootloader_support/test_apps/rtc_custom_section/sdkconfig.defaults

@@ -0,0 +1,3 @@
+CONFIG_BOOTLOADER_RESERVE_RTC_SIZE=0x10
+CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC=y
+CONFIG_BOOTLOADER_CUSTOM_RESERVE_RTC_SIZE=0x200