[example] Fiber overflow detection on ARMv8-M

Author: salkinium

examples/nucleo_u575zi-q/fiber_overflow/main.cpp

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+/*
+ * Copyright (c) 2024, Niklas Hauser
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#include <modm/board.hpp>
+#include <modm/processing.hpp>
+
+using namespace Board;
+using namespace std::chrono_literals;
+
+modm::Fiber<> blinky([]
+{
+	while(1)
+	{
+		Board::LedBlue::toggle();
+		modm::this_fiber::sleep_for(0.5s);
+	}
+});
+
+modm::Fiber<> bad_fiber([]
+{
+
+	MODM_LOG_INFO << "\nReboot!\nPush the button to overflow the stack!" << modm::endl;
+
+	while(1)
+	{
+		// cause stack overflow on button push
+		if (Button::read()) asm volatile ("push {r0-r7}");
+		modm::this_fiber::yield();
+	}
+});
+
+// On fiber stack overflow this handler will be called
+extern "C" void
+UsageFault_Handler()
+{
+	// check if the fault is a stack overflow *from the fiber stack*
+	if (SCB->CFSR & SCB_CFSR_STKOF_Msk and __get_PSP() == __get_PSPLIM())
+	{
+		// lower the priority of the usage fault to allow the UART interrupts to work
+		NVIC_SetPriority(UsageFault_IRQn, (1ul << __NVIC_PRIO_BITS) - 1ul);
+		// raise an assertion to report this overflow
+		modm_assert(false, "fbr.stkof", "Fiber stack overflow", modm::this_fiber::get_id());
+	}
+	else HardFault_Handler();
+}
+
+int
+main()
+{
+	Board::initialize();
+	// Enable the UsageFault handler
+	SCB->SHCSR |= SCB_SHCSR_USGFAULTENA_Msk;
+
+	modm::fiber::Scheduler::run();
+
+	return 0;
+}

examples/nucleo_u575zi-q/fiber_overflow/project.xml

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+<library>
+  <extends>modm:nucleo-u575zi-q</extends>
+  <options>
+    <option name="modm:build:build.path">../../../build/nucleo_u575zi-q/fiber_overflow</option>
+  </options>
+  <modules>
+    <module>modm:build:scons</module>
+    <module>modm:processing:fiber</module>
+  </modules>
+</library>