pack: clamp flash-algo RAM to the device's RAM region

pyocd/target/pack/flm_region_builder.py

@@ -1,6 +1,7 @@
 # pyOCD debugger
 # Copyright (c) 2022-2023 Chris Reed
 # Copyright (c) 2025 Arm Limited
+# Copyright (c) 2026 Evgeny Korolev
 # SPDX-License-Identifier: Apache-2.0
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -127,6 +128,17 @@ def _select_flash_ram(self, region: FlashRegion) -> RamRegion:
                     # so just use a mid-range arbitrary size.
                     ram_size = 16 * 1024
 
+            # Clamp the algo RAM to the containing RAM region, in case a DFP declares an
+            # <algorithm> RAMsize larger than the device's actual RAM.
+            containing_ram = self._memory_map.get_region_for_address(ram_start)
+            if (containing_ram is not None) and (containing_ram.type is MemoryType.RAM):
+                available = containing_ram.length - (ram_start - containing_ram.start)
+                if ram_size > available:
+                    LOG.warning("Flash algo for region '%s' requests %#x bytes of RAM at %#010x, "
+                                "but containing region '%s' only provides %#x; clamping to fit.",
+                                region.name, ram_size, ram_start, containing_ram.name, available)
+                    ram_size = available
+
             ram_for_algo = RamRegion(start=ram_start, length=ram_size)
         else:
             # No RAM addresses were given, so go with the RAM marked default.

test/unit/test_pack.py

@@ -1,6 +1,7 @@
 # pyOCD debugger
 # Copyright (c) 2019-2020 Arm Limited
 # Copyright (c) 2021-2023 Chris Reed
+# Copyright (c) 2026 Evgeny Korolev
 # SPDX-License-Identifier: Apache-2.0
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -356,6 +357,20 @@ def test_ram_select_explicit(self, builder: FlmFlashRegionBuilder, nrf5340appflm
         assert not flash.has_subregions
         assert flash.algo
 
+    def test_ram_select_explicit_clamped_to_region(self, builder: FlmFlashRegionBuilder, nrf5340appflm):
+        # _RAMsize (0x18000) exceeds the containing RAM region (0x20000000, length 0x10000), as
+        # happens with e.g. SiliconLabs' GeckoPlatform_EFR32MG21_DFP. The algo RAM must be clamped
+        # to the region so the loader (laid out from the top down) isn't placed past physical RAM.
+        flash = memory_map.FlashRegion(0, length=0x200000, flm=nrf5340appflm,
+                                        _RAMstart=0x20000000, _RAMsize=0x18000)
+        assert builder.finalise_region(flash)
+        assert flash.algo
+        instr_len = len(flash.algo['instructions']) * 4
+        # Clamped to the region end (0x20010000), not the oversized 0x20018000.
+        assert flash.algo['load_address'] == (0x20010000 - instr_len)
+        assert not flash.has_subregions
+        assert flash.algo
+
 def has_overlapping_regions(memmap):
     return any((len(memmap.get_intersecting_regions(r.start, r.end)) > 1) for r in memmap.regions)