Add atomic builtins implementation and example

examples/atomic/Makefile

@@ -0,0 +1,54 @@
+NAME=vector-test
+MCU=atmega328p
+F_CPU=16000000ul
+
+PROGRAMMER=arduino
+AVRDUDE_FLAGS= -P/dev/ttyUSB0 -b57600
+
+ifeq ($(STD),)
+STD=c++20
+endif
+
+BUILD_DIR=./build
+LIB_DIR=../..
+COMMON_DIR=../common
+
+INCLUDES=-I$(COMMON_DIR) -I$(LIB_DIR)/include
+
+SOURCES=$(wildcard *.cpp $(LIB_DIR)/src/*.cc)
+VPATH=.:$(LIB_DIR)/src:$(COMMON_DIR)
+OBJECTS=$(addprefix $(BUILD_DIR)/,$(notdir $(SOURCES:%=%.o)))
+
+CXXFLAGS=-std=$(STD) -Os -Wno-volatile --param=min-pagesize=0 -Wall -Wextra -pedantic -fno-exceptions -fno-rtti -fno-unwind-tables -fno-threadsafe-statics -Wshadow -Wcast-qual -Wpointer-arith -Wundef -DF_CPU=$(F_CPU)
+LDFLAGS=
+
+TARGET=$(BUILD_DIR)/$(NAME)
+
+all: hex size
+
+hex: $(TARGET).hex
+
+$(TARGET).hex: $(TARGET).elf
+	avr-objcopy -O ihex -j .data -j .text $(TARGET).elf $(TARGET).hex
+
+$(TARGET).elf: $(OBJECTS)
+	avr-g++ $(LDFLAGS) -mmcu=$(MCU) $(OBJECTS) -o $(TARGET).elf
+
+$(BUILD_DIR)/%.cpp.o: %.cpp
+	@mkdir -p $(BUILD_DIR)
+	avr-g++ -c $(CXXFLAGS) -mmcu=$(MCU) $(INCLUDES) $< -o $@
+
+$(BUILD_DIR)/%.cc.o: %.cc
+	@mkdir -p $(BUILD_DIR)
+	avr-g++ -c $(CXXFLAGS) -mmcu=$(MCU) $(INCLUDES) $< -o $@
+
+size: $(TARGET).elf
+	avr-objdump -Pmem-usage $(TARGET).elf
+
+program: $(TARGET).hex
+	avrdude -p$(MCU) $(AVRDUDE_FLAGS) -c$(PROGRAMMER) -Uflash:w:$(TARGET).hex:a
+
+clean:
+	rm -rf $(BUILD_DIR)/*.o
+	rm -rf $(BUILD_DIR)/*.elf
+	rm -rf $(BUILD_DIR)/*.hex

examples/atomic/atomic.cpp

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2022, Christopher Kormanyos
+ *
+ * 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 <atomic>
+#include <cstdint>
+
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <avr/wdt.h>
+
+static void app_hw_init();
+
+std::atomic<std::uint16_t> sequence;
+
+int main()
+{
+	// Initialize the application hardware. This includes WDT, PORTB.5 and TIMER0.
+	app_hw_init();
+
+	for(;;)
+	{
+		// Toggle the LED on portb.5.
+		PINB = (1U << PORTB5);
+
+		sequence++;
+	}
+}
+
+static void app_hw_init()
+{
+	// Initialize the application including WDT, PORTB.5 and TIMER0
+
+	// We will now disable the watchdog.
+	// Service the watchdog just to be sure to avoid pending timeout.
+	wdt_reset();
+
+	// Clear WDRF in MCUSR.
+	MCUSR &= ~(1U << WDRF);
+
+	// Write logical one to WDCE and WDE.
+	// Keep the old prescaler setting to prevent unintentional time-out.
+	WDTCSR |= (1U << WDCE) | (1U << WDE);
+
+	// Turn off the WDT.
+	WDTCSR = 0x00;
+
+	// We will now initialize PORTB.5 to be used as an LED driver port.
+	// Set PORTB.5 value to low.
+	PORTB &= ~(1U << PORTB5);
+
+	// Set PORTB.5 direction to output.
+	DDRB |= (1U << DDB5);
+
+	// We will now initialize the TIMER0 clock and interrupt.
+	// Clear the TIMER0 overflow flag.
+	TIFR0 = static_cast<std::uint8_t>(1U << TOV0);
+
+	// Enable the TIMER0 overflow interrupt.
+	TIMSK0 = static_cast<std::uint8_t>(1U << TOIE0);
+
+	// Set the TIMER0 clock source to f_osc/8 = 2MHz and begin counting.
+	TCCR0B = static_cast<std::uint8_t>(1U << CS01);
+
+	// Enable all interrupts.
+	sei();
+}
+
+
+
+ISR(TIMER0_OVF_vect)
+{
+	sequence++;
+}

include/atomic

@@ -34,6 +34,10 @@
 
 #pragma GCC system_header
 
+#if __has_include(<bits/atomic_builtins.h>)
+# include <bits/atomic_builtins.h>
+#endif
+
 #if __cplusplus < 201103L
 # include <bits/c++0x_warning.h>
 #else