pkg/flashdb: add configurable sector size

pkg/flashdb/Kconfig

@@ -41,6 +41,15 @@ config MODULE_FLASHDB_KVDB_AUTO_UPDATE
           database. If the version changes, it will automatically trigger an upgrade action
           and update the new default KV collection to the current database.
 
+config FLASHDB_MIN_SECTOR_SIZE_DEFAULT_KiB
+    int "Minimal virtual sector size in KiB for FlashDB"
+    default 4
+    help
+        By default, KVDB will use 1 times the block size as the sector size, that is, 4096.
+        At this time, the KVDB cannot store a KV longer than 4096. If you want to save, for example,
+        a KV with a length of 10K, you can use the control function to set the sector size to 12K or
+        larger.
+
 config MODULE_FLASHDB_MTD
 
 endif # PACKAGE_FLASHDB

pkg/flashdb/include/fal_cfg.h

@@ -26,12 +26,40 @@
 #define FAL_CFG_H
 
 #include "board.h"
+#include "macros/units.h"
 #include "mtd_default.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(CONFIG_FLASHDB_MIN_SECTOR_SIZE_DEFAULT_KiB) || defined(DOXYGEN)
+/**
+ * @brief   Minimal virtual sector size in KiB for FlashDB
+ *
+ * This is just a reasonable default for an automatic partition configuration, hence "DEFAULT".
+ * The "MIN" stands for a required minimum to guarantee an expected size of key value pairs.
+ * The actually acceptable sector size must be a multiple of the physical sector size though.
+ * Thus, it can be larger than the minimum required size.
+ *
+ * The default is 4 (4096).
+ * FlashDB sector size is different from MTD sector size as it is a
+ * virtual measure of granularity and not a device property.
+ * The virtual sector size must be a multiple of the physical sector size.
+ *
+ * From the documentation of FLashDB:
+ * The internal storage structure of FlashDB is composed of N sectors, and each formatting takes
+ * sector as the smallest unit. A sector is usually N times the size of the Flash block.
+ * For example, the block size of Nor Flash is generally 4096.
+ *
+ * By default, KVDB will use 1 times the block size as the sector size, that is, 4096.
+ * At this time, the KVDB cannot store a KV longer than 4096. If you want to save, for example,
+ * a KV with a length of 10K, you can use the control function to set the sector size to 12K or larger.
+ *
+ */
+#define CONFIG_FLASHDB_MIN_SECTOR_SIZE_DEFAULT_KiB  4
+#endif
+
 /**
  * @brief   Partition table is defined at compile time (not read from flash)
  */
@@ -66,9 +94,15 @@ extern struct fal_flash_dev mtd_flash0;
 
 #if !defined(FAL_PART0_LENGTH) || defined(DOXYGEN)
 /**
- * @brief   Have at least the length of partition 0 defined
+ * @brief   Have at least the length of partition 0 defined, which must be at least two sectors
+ *          and a multiple of the virtual sector size.
+ *
+ * The virtual sector size is however bound to the physical sector size of @ref FAL_MTD.
+ * So make sure that @ref CONFIG_FLASHDB_MIN_SECTOR_SIZE_DEFAULT_KiB times 1024 is a multiple of the MTD sector size.
+ * For example if the MTD sector size is 4KiB, then @ref CONFIG_FLASHDB_MIN_SECTOR_SIZE_DEFAULT_KiB must be a multiple of 4.
+ * If the MTD sector size is 1KiB, then you have all options for @ref CONFIG_FLASHDB_MIN_SECTOR_SIZE_DEFAULT_KiB.
  */
-#define FAL_PART0_LENGTH                            (2 * 4096u)
+#define FAL_PART0_LENGTH                            (2 * (CONFIG_FLASHDB_MIN_SECTOR_SIZE_DEFAULT_KiB * KiB(1)))
 #endif
 
 /**