Switch QEMU from NETDUINOPLUS2 to B-L475E-IOT01A

This replaces Netduino Plus 2 (STM32F4) QEMU target with B-L475E-IOT01A
Discovery (STM32L475VG) for proper FPU/MPU emulation, eliminating the
mock infrastructure (mpu_mock, scb_mock, safe_mmio) that was papering
over the old target's incomplete peripheral emulation.

Platform changes:
- Add STM32L4 platform support (registers, GPIO, RCC, USART, NVIC,
  linker scripts with correct L4 memory map and no CCM RAM)
- Fix L4 register addresses: USART1 at 0x40013800, RCC enable
  registers at correct L4 offsets, GPIO clocks on AHB2 (not AHB1),
  PLL source set to MSI (not HSE), USART_IT_CR offsets for L4
- Add full L4 USART register ops (ISR/RDR/TDR layout)
- Add ARM semihosting for console I/O under QEMU

FPU support:
- Fix irq_restore: single asm block with __builtin_offsetof prevents
  compiler from reusing clobbered registers after ldm {r4-r11}
- Add -mgeneral-regs-only to kernel CFLAGS to prevent GCC from
  emitting VFP instructions for non-FP operations in handler mode
- Add FPU lazy context save/restore (d8-d15) in PendSV handler

IPC fix:
- Fix L4_Ipc naked function: reload UTCB MR pointer from
  current_utcb after SVC return instead of reusing LR (which the
  exception frame restores to the caller's return address)

KDB:
- Add USART1 RX interrupt path for KDB input under QEMU semihosting
  (CONFIG_KDB_UART_INPUT, gated on CONFIG_QEMU)
- Improve hard fault handler to read correct stack (MSP vs PSP)

Build/test:
- Update qemu-test.py: auto-detect board, add -semihosting for L4,
  fail on unsupported boards instead of silent fallback
- Bootstrap Kconfig tools in CI test job before direct Python usage
- Update CI workflow: replace netduinoplus2 with b-l475e-iot01a
- Remove Netduino Plus 2 board, STM32F1 platform, mock infrastructure

Author: jserv

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-24.04
     strategy:
       matrix:
-        board: [discoveryf4, discoveryf429, netduinoplus2]
+        board: [discoveryf4, discoveryf429, b-l475e-iot01a]
 
     steps:
     - uses: actions/checkout@v6
@@ -66,14 +66,28 @@ jobs:
         release: '15.2.Rel1'
 
     - name: Install QEMU
-      run: sudo apt-get update && sudo apt-get install -y qemu-system-arm
-
-    - name: Configure for netduinoplus2 with ${{ matrix.name }}
+      env:
+        GH_TOKEN: ${{ github.token }}
+        QEMU_VERSION: '10.2.2'
+      run: |
+        # Download prebuilt QEMU from GitHub release (built by qemu-build.yml)
+        asset="qemu-${QEMU_VERSION}-arm-softmmu-linux-x86_64.tar.gz"
+        gh release download "qemu-v${QEMU_VERSION}" \
+          --pattern "$asset" \
+          --dir /tmp
+        sudo tar -xzf "/tmp/${asset}" -C /opt
+        echo "/opt/qemu/bin" >> "$GITHUB_PATH"
+        /opt/qemu/bin/qemu-system-arm --version
+        /opt/qemu/bin/qemu-system-arm -M help | awk '{print $1}' | grep -Fx b-l475e-iot01a
+
+    - name: Configure for b-l475e-iot01a with ${{ matrix.name }}
       run: |
-        make netduinoplus2_defconfig
-        # Enable QEMU mode and selected test suite
+        # Bootstrap Kconfig tools (cloned on demand by make, but we
+        # need them before the first make invocation here)
+        make tools/kconfig/kconfiglib.py
+        cp board/b-l475e-iot01a/defconfig .config
+        # Enable selected test suite on top of board defaults
         python3 tools/kconfig/setconfig.py \
-          QEMU=y \
           ${{ matrix.config }}=y
         python3 tools/kconfig/genconfig.py --header-path include/autoconf.h Kconfig
 
@@ -91,7 +105,7 @@ jobs:
     - name: Run MPU fault test
       if: matrix.app == 'tests'
       run: make run-tests FAULT=mpu
-      continue-on-error: true  # MPU not fully emulated in QEMU
+      continue-on-error: true  # MPU fault test may behave differently under QEMU
 
     - name: Run stack canary fault test
       if: matrix.app == 'tests'

.github/workflows/qemu-build.yml

@@ -0,0 +1,76 @@
+name: Build QEMU
+
+# Build a minimal QEMU (arm-softmmu only) and upload as a GitHub release.
+# The test jobs in build.yml download this prebuilt binary instead of
+# compiling QEMU from source on every run.
+#
+# Trigger manually or bump QEMU_VERSION to rebuild.
+
+on:
+  workflow_dispatch:
+    inputs:
+      qemu_version:
+        description: 'QEMU version to build (e.g. 10.2.2)'
+        required: true
+        default: '10.2.2'
+
+env:
+  QEMU_VERSION: ${{ inputs.qemu_version || '10.2.2' }}
+
+permissions:
+  contents: write  # create releases
+
+jobs:
+  build:
+    runs-on: ubuntu-24.04
+    steps:
+    - uses: actions/checkout@v6
+
+    - name: Validate version format
+      run: |
+        if ! echo "${QEMU_VERSION}" | grep -qE '^[0-9]+\.[0-9]+\.[0-9]+$'; then
+          echo "ERROR: Invalid QEMU_VERSION '${QEMU_VERSION}' (expected N.N.N)"
+          exit 1
+        fi
+
+    - name: Install build dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y ninja-build pkg-config libglib2.0-dev libpixman-1-dev
+
+    - name: Build QEMU ${{ env.QEMU_VERSION }} (arm-softmmu)
+      run: |
+        curl -sL "https://download.qemu.org/qemu-${QEMU_VERSION}.tar.xz" | tar xJ
+        cd "qemu-${QEMU_VERSION}"
+        ./configure \
+          --target-list=arm-softmmu \
+          --prefix=/opt/qemu \
+          --disable-docs
+        make -j$(nproc)
+        sudo make install
+
+    - name: Verify
+      run: |
+        /opt/qemu/bin/qemu-system-arm --version
+        /opt/qemu/bin/qemu-system-arm -M help | awk '{print $1}' | grep -Fx b-l475e-iot01a
+
+    - name: Package
+      run: |
+        tar -czf "qemu-${QEMU_VERSION}-arm-softmmu-linux-x86_64.tar.gz" -C /opt qemu
+
+    - name: Create release
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        tag="qemu-v${QEMU_VERSION}"
+        asset="qemu-${QEMU_VERSION}-arm-softmmu-linux-x86_64.tar.gz"
+
+        # Upload to existing release, or create a new one.
+        # Upload first so the old asset stays available until replaced.
+        if gh release view "$tag" >/dev/null 2>&1; then
+          gh release upload "$tag" "$asset" --clobber
+        else
+          gh release create "$tag" "$asset" \
+            --title "QEMU ${QEMU_VERSION} (arm-softmmu, linux-x86_64)" \
+            --notes "Prebuilt QEMU ${QEMU_VERSION} (arm-softmmu only) for CI test jobs."
+        fi

Documentation/quick-start.md

@@ -7,8 +7,8 @@ F9 Microkernel supports the following boards:
 * [STM32F429I-DISC1](https://www.st.com/en/evaluation-tools/32f429idiscovery.html)
 * [NUCLEO-F429ZI](https://www.st.com/en/evaluation-tools/nucleo-f429zi.html)
   - All supported boards are based on the ARM Cortex-M4F core. F9 should work on any STM32F40x/STM32F429/STM32F439 microcontroller.
-* Netduino Plus 2 (STM32F405RGT6)
-  - Supported by upstream [QEMU for emulation](https://www.qemu.org/docs/master/system/arm/stm32.html), making it ideal for development and testing without hardware.
+* [B-L475E-IOT01A](https://www.st.com/en/evaluation-tools/b-l475e-iot01a.html)
+  - Supported by upstream QEMU and used as the default emulation target.
 
 ## Toolchain Requirements
 
@@ -89,16 +89,18 @@ KDB communicates via USART. The port can be selected during `make config`.
 
 ## QEMU Emulation
 
-For Netduino Plus 2 under QEMU, the default configuration uses USART1, which
-QEMU routes to the console. Run with:
+For B-L475E-IOT01A under QEMU, semihosting carries normal console output and
+USART1 is reserved for KDB input. Run with:
 
 ```shell
-qemu-system-arm -M netduinoplus2 -nographic -serial mon:stdio \
-    -kernel build/netduinoplus2/f9.elf
+qemu-system-arm -M b-l475e-iot01a -nographic \
+    -semihosting -serial mon:stdio \
+    -kernel build/b-l475e-iot01a/f9.elf
 ```
 
-Note: `-serial mon:stdio` is required for interactive KDB shell.
-The `mon:` prefix enables QEMU monitor access via `Ctrl+a` and `c`. Exit with `Ctrl+a` and `x`.
+Note: `-serial mon:stdio` is still required for interactive KDB shell.
+The `mon:` prefix enables QEMU monitor access via `Ctrl+A` then `c`. Exit with
+`Ctrl+A` then `x`.
 
 ## Serial Terminal Setup
 

Makefile

@@ -16,10 +16,10 @@ endif
 
 ifeq "$(CONFIG_BOARD_STM32F429DISCOVERY)" "y"
 BOARD ?= discoveryf429
-else ifeq "$(CONFIG_BOARD_NETDUINOPLUS2)" "y"
-BOARD ?= netduinoplus2
 else ifeq "$(CONFIG_BOARD_STM32F429NUCLEO)" "y"
 BOARD ?= nucleof429
+else ifeq "$(CONFIG_BOARD_B_L475E_IOT01A)" "y"
+BOARD ?= b-l475e-iot01a
 else
 BOARD ?= discoveryf4
 endif
@@ -32,8 +32,9 @@ out ?= build/$(BOARD)
 # output directory for host build targets
 out_host ?= build/host
 
-# QEMU command for netduinoplus2 emulation
-# Usage: qemu-system-arm -M netduinoplus2 -nographic -kernel build/netduinoplus2/f9.elf
+# QEMU emulation support (auto-detects board from build path)
+# Usage: make run-tests
+# Direct: qemu-system-arm -M b-l475e-iot01a -nographic -kernel build/b-l475e-iot01a/f9.elf
 QEMU ?= qemu-system-arm
 
 includes-user = user/include
@@ -114,8 +115,12 @@ include mk/generic.mk
 
 # Run tests with clean output (filtered debug messages)
 .PHONY: qemu-clean
-qemu-clean:
+qemu-clean: $(out)/f9.elf
 	@echo "Running F9 tests (clean output)..."
-	@python3 scripts/qemu-test.py $(out)/f9.elf -t 75 2>&1 | \
+	@$(PYTHON) scripts/qemu-test.py $(out)/f9.elf -t 75 2>&1 | \
 		grep -vE "^(IPC: |pager_|THREAD_CREATE:)" | \
 		grep -vE "^\[TEST:(RUN|PASS|FAIL|SKIP|START)\]" || true
+
+# Note: 'make run-tests' target defined in mk/generic.mk
+# Supports fault testing: make run-tests FAULT=mpu
+# Auto-detects board and QEMU machine from build path

README.md

@@ -33,10 +33,10 @@ while adding advanced features from industrial RTOSes.
 - UTCBs: Always-mapped user-level thread control blocks for fast syscall argument access
 
 ### Hardware Support
-- ARM Cortex-M3/M4/M4F: Optimized for Cortex-M architecture
+- ARM Cortex-M4/M4F: Optimized for Cortex-M architecture
 - NVIC: Nested Vectored Interrupt Controller integration
 - Bit Banding: Hardware bit manipulation support (where available)
-- FPU: Lazy context switching for Cortex-M4F floating-point unit
+- FPU: Lazy context switching for Cortex-M4F floating-point unit (VFPv4-D16)
 
 ### Development Tools
 - KDB: In-kernel debugger with thread, memory, and timer inspection
@@ -124,13 +124,16 @@ make flash     # Flash to STM32F4 board (requires stlink)
 make qemu
 ```
 
-Press `Ctrl+A` and then `X` to exit QEMU. Press `?` in KDB for debug menu (requires `CONFIG_KDB`).
+Press `Ctrl+A` then `X` to exit QEMU. Press `?` for KDB debug menu (requires `CONFIG_KDB`).
+
+QEMU uses the B-L475E-IOT01A machine with ARM semihosting for output and USART1
+for KDB input. Both `-semihosting` and `-serial mon:stdio` are added automatically.
 
 ### Supported Hardware
 - STM32F4DISCOVERY (STM32F407VG)
 - STM32F429I-DISC1 (STM32F429ZI)
 - NUCLEO-F429ZI (STM32F429ZI)
-- Netduino Plus 2 (STM32F405RG) - QEMU only, used for automated testing
+- B-L475E-IOT01A (STM32L475VG) - QEMU target with FPU and MPU emulation
 
 For detailed instructions including toolchain setup, serial configuration, and debugging,
 see [Documentation/quick-start.md](Documentation/quick-start.md).
@@ -149,8 +152,9 @@ Run `make config` to configure options via menu. Key options:
 | `CONFIG_KTIMER_TICKLESS` | Tickless scheduling (power efficiency) |
 | `CONFIG_MAX_THREADS` | Maximum number of threads |
 | `CONFIG_MAX_KT_EVENTS` | Maximum kernel timer events |
+| `CONFIG_FPU` | FPU support with lazy context switching (Cortex-M4F) |
 | `CONFIG_PANIC_DUMP_STACK` | Dump stack on kernel panic |
-| `CONFIG_QEMU` | QEMU emulation workarounds |
+| `CONFIG_QEMU` | QEMU emulation mode (auto-enabled for B-L475E-IOT01A) |
 
 For build system details, see [Documentation/build-system.md](Documentation/build-system.md).
 

board/Kconfig

@@ -22,32 +22,38 @@ config BOARD_STM32F429DISCOVERY
 	help
 	  STM32F429 Discovery board with STM32F429ZIT6 MCU and LCD.
 
-config BOARD_NETDUINOPLUS2
-	bool "Netduino Plus 2"
-	select PLATFORM_STM32F4
-	help
-	  Netduino Plus 2 board with STM32F405RGT6 MCU.
-	  This board is supported by upstream QEMU for emulation.
-
 config BOARD_STM32F429NUCLEO
 	bool "STM32F429 Nucleo"
 	select PLATFORM_STM32F429
 	help
 	  STM32F429 Nucleo board with STM32F429ZIT6 MCU.
 
+config BOARD_B_L475E_IOT01A
+	bool "B-L475E-IOT01A Discovery"
+	select PLATFORM_STM32L4
+	select QEMU
+	help
+	  STMicroelectronics B-L475E-IOT01A Discovery board with STM32L475VG MCU.
+	  Includes Cortex-M4F with FPU, MPU, and full QEMU support with FPU emulation.
+	  QEMU mode is automatically enabled for this board.
+
+	  QEMU command:
+	  qemu-system-arm -M b-l475e-iot01a -nographic -kernel build/b-l475e-iot01a/f9.elf
+
 endchoice
 
 config QEMU
-	bool "QEMU emulation mode"
-	default y if BOARD_NETDUINOPLUS2
+	bool "QEMU emulation mode" if !BOARD_B_L475E_IOT01A
 	help
 	  Enable workarounds for QEMU emulation limitations:
-	  - Use synchronous UART output (QEMU TXE interrupt unreliable)
-	  - Place bitmaps in regular SRAM (QEMU lacks CCM RAM emulation)
+	  - Use semihosting for console I/O (reliable in QEMU)
+	  - Use synchronous UART output if UART is selected
 
 	  Enable this when running under QEMU. Disable for real hardware
 	  to get better performance.
 
+	  Note: Automatically enabled and mandatory for B-L475E-IOT01A board.
+
 # Hardware feature availability flags
 # These control which ARM architecture tests can run based on
 # platform capabilities and emulation limitations.
@@ -65,29 +71,6 @@ config HAS_PRECISE_TIMING
 
 	  Disabled in QEMU because timing is not cycle-accurate.
 
-config MPU_MOCK
-	bool "Software MPU mock for testing"
-	depends on QEMU
-	default y if QEMU
-	help
-	  Enable minimal MPU register mock for test_arm_mpu_config in QEMU.
-
-	  Returns MPU_TYPE = 0x800 (8 regions, unified) to validate that
-	  MPU_TYPE register is readable without QEMU hanging.
-
-	  For full MPU validation, test on real hardware with actual MPU.
-
-config SCB_MOCK
-	bool "Software SCB mock for testing"
-	depends on QEMU
-	default y if QEMU
-	help
-	  Enable minimal SCB register mock for test_arm_unaligned in QEMU.
-
-	  Returns SCB_CCR = 0x200 (STKALIGN enabled, UNALIGN_TRP disabled)
-	  to validate SCB_CCR register readability without QEMU hanging.
-
-	  For full SCB validation, test on real hardware with actual SCB.
 
 endmenu
 
@@ -97,3 +80,6 @@ config PLATFORM_STM32F4
 
 config PLATFORM_STM32F429
 	bool
+
+config PLATFORM_STM32L4
+	bool

board/netduinoplus2/board.c board/b-l475e-iot01a/board.cboard/netduinoplus2/board.c renamed to board/b-l475e-iot01a/board.c

@@ -4,11 +4,11 @@
  */
 
 #include "board.h"
-#include <platform/stm32f4/gpio.h>
-#include <platform/stm32f4/usart.h>
+#include <platform/stm32l4/gpio.h>
+#include <platform/stm32l4/usart.h>
 
 struct usart_dev console_uart = {
-    .u_num = 2,
+    .u_num = 1,
     .baud = 115200,
     BOARD_USART_CONFIGS.tx =
         {

board/b-l475e-iot01a/board.h

@@ -0,0 +1,29 @@
+/* Copyright (c) 2013-2014 The F9 Microkernel Project. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef B_L475E_IOT01A_BOARD_H_
+#define B_L475E_IOT01A_BOARD_H_
+
+#include <platform/stm32l4/gpio.h>
+#include <platform/stm32l4/nvic.h>
+#include <platform/stm32l4/registers.h>
+#include <platform/stm32l4/systick.h>
+#include <platform/stm32l4/usart.h>
+
+extern struct usart_dev console_uart;
+
+/* ST-Link VCP uses USART1: PB6 (TX), PB7 (RX) */
+#define BOARD_UART_DEVICE USART1_IRQn
+#define BOARD_UART_HANDLER USART1_HANDLER
+#define BOARD_USART_FUNC af_usart1
+#define BOARD_USART_CONFIGS                               \
+    .base = USART1_BASE, .rcc_apbenr = RCC_USART1_APBENR, \
+    .rcc_reset = RCC_APB2RSTR_USART1RST,
+#define BOARD_USART_TX_IO_PORT GPIOB
+#define BOARD_USART_TX_IO_PIN 6
+#define BOARD_USART_RX_IO_PORT GPIOB
+#define BOARD_USART_RX_IO_PIN 7
+
+#endif /* B_L475E_IOT01A_BOARD_H_ */

board/netduinoplus2/build.mk board/b-l475e-iot01a/build.mkboard/netduinoplus2/build.mk renamed to board/b-l475e-iot01a/build.mk

@@ -2,9 +2,9 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-CHIP := stm32f4
+CHIP := stm32l4
 PLATFORM := stm32
-STM32_VARIANT := f4
+STM32_VARIANT := l4
 
 board-y = board.o
 loader-board-y = board.loader.o

board/b-l475e-iot01a/defconfig

@@ -0,0 +1,2 @@
+CONFIG_BOARD_B_L475E_IOT01A=y
+CONFIG_FPU=y