pack: builder: take the erased byte value from the FLM without subregions too

pyocd/target/pack/flm_region_builder.py

@@ -167,10 +167,10 @@ def _update_flash_attributes(
         if create_subregions:
             self._add_flash_subregions(region, pack_algo, page_size, algo)
         else:
-            # Set attributes on parent flash region. The parent region still has to have these attributes
-            # even though there are subregions.
+            # Set parent flash region attributes without creating subregions.
             region.attributes['page_size'] = page_size
             region.attributes['sector_size'] = sector_sizes[0][1]
+            region.attributes['erased_byte_value'] = pack_algo.flash_info.value_empty
 
     def _add_flash_subregions(
             self,
@@ -228,3 +228,4 @@ def _add_flash_subregions(
         # even though there are subregions.
         region.attributes['page_size'] = page_size
         region.attributes['sector_size'] = max_sector_size
+        region.attributes['erased_byte_value'] = pack_algo.flash_info.value_empty

test/unit/test_pack.py

@@ -1,5 +1,5 @@
 # pyOCD debugger
-# Copyright (c) 2019-2020 Arm Limited
+# Copyright (c) 2019-2020,2026 Arm Limited
 # Copyright (c) 2021-2023 Chris Reed
 # SPDX-License-Identifier: Apache-2.0
 #
@@ -337,6 +337,22 @@ def test_multiple_sector_size(self, builder: FlmFlashRegionBuilder, stm32f42mflm
         assert submap[4].sector_size == 0x10000
         assert submap[5].sector_size == 0x20000
 
+    def test_single_sector_size_erased_value(self, builder: FlmFlashRegionBuilder, nrf5340appflm, monkeypatch):
+        monkeypatch.setattr(nrf5340appflm.flash_info, 'value_empty', 0x00)
+        flash = memory_map.FlashRegion(0, length=0x200000, flm=nrf5340appflm)
+        assert flash.erased_byte_value == 0xff
+        assert builder.finalise_region(flash)
+        assert not flash.has_subregions
+        assert flash.erased_byte_value == 0x00
+
+    def test_multiple_sector_size_erased_value(self, builder: FlmFlashRegionBuilder, stm32f42mflm, monkeypatch):
+        monkeypatch.setattr(stm32f42mflm.flash_info, 'value_empty', 0x00)
+        flash = memory_map.FlashRegion(0x08000000, length=0x200000, flm=stm32f42mflm)
+        assert builder.finalise_region(flash)
+        assert flash.has_subregions
+        assert flash.erased_byte_value == 0x00
+        assert all(subregion.erased_byte_value == 0x00 for subregion in flash.submap)
+
     def test_ram_select_default(self, builder: FlmFlashRegionBuilder, nrf5340appflm):
         flash = memory_map.FlashRegion(0, length=0x200000, flm=nrf5340appflm)
         builder.finalise_region(flash)