zephyr: Add erase block size to FlashArea.areas entries.

This commit changes the values in the `FlashArea.areas` dictionary from
simple integer IDs to (ID, erase-block-size) tuples.

`_boot.py` was changed to use the newly available erase block size.

Signed-off-by: Ned Konz <ned@metamagix.tech>

3 files changed, 48 insertions, 3 deletions

diff --git a/ports/zephyr/README.md b/ports/zephyr/README.md
index 480ff5705..eedcdcb58 100644
--- a/ports/zephyr/README.md
+++ b/ports/zephyr/README.md
@@ -163,6 +163,28 @@ the 'io-channels' property with all the ADC channels):
     adc = ADC(("adc", 0))
     adc.read_uv()
 
+Example of using FlashArea for flash storage access:
+
+    from zephyr import FlashArea
+
+    # FlashArea.areas is a dictionary mapping partition labels to tuples
+    # Each tuple contains (partition_id, erase_block_size)
+    print(FlashArea.areas)  # e.g. {'storage': (3, 4096)}
+
+    # Create a FlashArea object for a specific partition
+    # Constructor takes (partition_id, block_size)
+    partition_id, erase_size = FlashArea.areas['storage']
+    flash = FlashArea(partition_id, erase_size)
+
+    # Use with virtual filesystem (see _boot.py for automatic mounting)
+    import os
+    os.VfsFat(flash)  # or os.VfsLfs2(flash)
+
+The `FlashArea.areas` dictionary provides partition information from the Zephyr
+devicetree. The erase block size is obtained from the flash controller's
+`erase-block-size` property, or defaults to 4096 bytes for devices (like QSPI
+NOR flash) that don't specify this property.
+
 Minimal build
 -------------
 
diff --git a/ports/zephyr/modules/_boot.py b/ports/zephyr/modules/_boot.py
index 5af302fad..d0ba21d3f 100644
--- a/ports/zephyr/modules/_boot.py
+++ b/ports/zephyr/modules/_boot.py
@@ -23,8 +23,7 @@ def create_flash_partition():
     Return True if successful, False otherwise.
     """
     if _STORAGE_KEY in FlashArea.areas:
-        # TODO: get the erase block size from DTS instead of 4K.
-        bdev = FlashArea(FlashArea.areas[_STORAGE_KEY], 4096)
+        bdev = FlashArea(*FlashArea.areas[_STORAGE_KEY])
         retval = True
         try:
             vfs.mount(bdev, _FLASH)
diff --git a/ports/zephyr/zephyr_storage.c b/ports/zephyr/zephyr_storage.c
index e72e047d0..b6396e711 100644
--- a/ports/zephyr/zephyr_storage.c
+++ b/ports/zephyr/zephyr_storage.c
@@ -184,15 +184,39 @@ MP_DEFINE_CONST_OBJ_TYPE(
 #define FLASH_AREA_DEFINE_GETNAME(part) COND_CODE_1(DT_NODE_HAS_PROP(part, label), \
     (FLASH_AREA_DEFINE_LABEL(part)), (FLASH_AREA_DEFINE_NB(part)))
 
-#define FLASH_AREA_DEFINE_DEFINE(part) { MP_ROM_QSTR(FLASH_AREA_DEFINE_GETNAME(part)), MP_ROM_INT(DT_FIXED_PARTITION_ID(part)) },
+// Helper macro to get erase block size from the flash device
+// Note: Some flash controllers have erase-block-size, others (like QSPI NOR) don't
+// For devices without this property, use 4096 as a common default for NOR flash
+#define FLASH_AREA_GET_ERASE_SIZE(part) \
+    DT_PROP_OR(DT_MTD_FROM_FIXED_PARTITION(part), erase_block_size, 4096)
+
+// Create a static tuple for each partition containing (id, erase_block_size)
+#define FLASH_AREA_DEFINE_TUPLE(part) \
+    static const mp_rom_obj_tuple_t flash_area_tuple_##part = { \
+        {&mp_type_tuple}, \
+        2, \
+        { \
+            MP_ROM_INT(DT_FIXED_PARTITION_ID(part)), \
+            MP_ROM_INT(FLASH_AREA_GET_ERASE_SIZE(part)), \
+        } \
+    };
+
+#define FLASH_AREA_TUPLE(part) COND_CODE_1(DT_NODE_HAS_STATUS_OKAY(DT_MTD_FROM_FIXED_PARTITION(part)), \
+    (FLASH_AREA_DEFINE_TUPLE(part)), ())
+
+#define FLASH_AREA_DEFINE_DEFINE(part) { MP_ROM_QSTR(FLASH_AREA_DEFINE_GETNAME(part)), MP_ROM_PTR(&flash_area_tuple_##part) },
 
 #define FLASH_AREA_DEFINE(part) COND_CODE_1(DT_NODE_HAS_STATUS_OKAY(DT_MTD_FROM_FIXED_PARTITION(part)), \
     (FLASH_AREA_DEFINE_DEFINE(part)), ())
 
 #define FOREACH_PARTITION(n) DT_FOREACH_CHILD(n, FLASH_AREA_DEFINE)
+#define FOREACH_PARTITION_TUPLE(n) DT_FOREACH_CHILD(n, FLASH_AREA_TUPLE)
 
 const mp_obj_type_t zephyr_flash_area_type;
 
+// Generate tuple definitions for all partitions
+DT_FOREACH_STATUS_OKAY(fixed_partitions, FOREACH_PARTITION_TUPLE)
+
 typedef struct _zephyr_flash_area_obj_t {
     mp_obj_base_t base;
     const struct flash_area *area;