MV2 ethos-u55: build-only CI check, update README

Instead of fully skipping ethos-u55 for MV2, run export + build (no FVP)
so link/compile regressions are still caught.  Split the README block into
a build-only marker for Corstone-300 and add a note about the 2 MiB ISRAM
limitation.  Also removes the dead ethos-u55 board-selection branch that
the earlier skip made unreachable.

Co-authored-by: Claude <noreply@anthropic.com>

Author: psiddh

.github/workflows/trunk.yml

@@ -191,14 +191,6 @@ jobs:
             continue
           fi
 
-          if [[ ${TARGET} == "ethos-u55" ]]; then
-            echo "---- Skipping MV2 for ${TARGET} (Corstone-300 ISRAM too small for MV2 runtime pools) ----"
-            continue
-          fi
-
-          echo "---- MV2 ${TARGET} ----"
-          rm -Rf build
-
           if [[ ${TARGET} == "ethos-u55" ]]; then
             BOARD="corstone300"
           elif [[ ${TARGET} == "ethos-u85" ]]; then
@@ -208,14 +200,22 @@ jobs:
             exit 1
           fi
 
+          echo "---- MV2 ${TARGET} ----"
+          rm -Rf build
+
           echo "---- MV2 ${TARGET} Board ${BOARD} FVP setup ----"
           run_command_block_from_readme "${ZEPHYR_SAMPLES_README_PATH}" "<!-- RUN setup_${BOARD}_fvp -->"
 
           echo "---- MV2 ${TARGET} Create PTE ----"
           run_command_block_from_readme "${MV2_README_PATH}" "<!-- RUN test_mv2_${TARGET}_generate_pte -->"
 
-          echo "---- MV2 ${TARGET} Build and run ----"
-          run_command_block_from_readme "${MV2_README_PATH}" "<!-- RUN test_mv2_${TARGET}_build_and_run -->"
+          if [[ ${TARGET} == "ethos-u55" ]]; then
+            echo "---- MV2 ${TARGET} Build only (Corstone-300 ISRAM too small for runtime pools) ----"
+            run_command_block_from_readme "${MV2_README_PATH}" "<!-- RUN test_mv2_${TARGET}_build -->"
+          else
+            echo "---- MV2 ${TARGET} Build and run ----"
+            run_command_block_from_readme "${MV2_README_PATH}" "<!-- RUN test_mv2_${TARGET}_build_and_run -->"
+          fi
         done
 
   test-models-linux-aarch64:

zephyr/samples/mv2-ethosu/README.md

@@ -14,6 +14,10 @@ The model classifies a static RGB test input tensor with shape `[1, 3, 224, 224]
 
 ## Corstone-300 FVP (Ethos-U55)
 
+> **Note:** Corstone-300 has only 2 MiB ISRAM. The MV2 allocator pools require
+> ~3 MiB, so the build will link but FVP execution will fail at runtime.
+> Use Corstone-320 (below) for end-to-end MV2 inference.
+
 ### Export the model
 
 Export a quantized INT8 MobileNetV2 model with Ethos-U55 delegation:
@@ -23,11 +27,11 @@ Export a quantized INT8 MobileNetV2 model with Ethos-U55 delegation:
 python -m modules.lib.executorch.backends.arm.scripts.aot_arm_compiler --model_name=mv2_untrained --quantize --delegate --target=ethos-u55-128 --output=mv2_u55_128.pte
 ```
 
-### Build and run
+### Build (link-check only)
 
-<!-- RUN test_mv2_ethos-u55_build_and_run -->
+<!-- RUN test_mv2_ethos-u55_build -->
 ```
-west build -b mps3/corstone300/fvp modules/lib/executorch/zephyr/samples/mv2-ethosu -t run -- -DET_PTE_FILE_PATH=mv2_u55_128.pte
+west build -b mps3/corstone300/fvp modules/lib/executorch/zephyr/samples/mv2-ethosu -- -DET_PTE_FILE_PATH=mv2_u55_128.pte
 ```
 
 ## Corstone-320 FVP (Ethos-U85)