AVRのソースを表示

[[カテゴリ:開発]]
[[en:AVR]]
[[Wikipedia:AVR_microcontrollers|AVR]] is a family of microcontrollers (MCUs) developed by Microchip Technology (former AVR). AVRs are especially common in hobbyist and educational embedded applications, popularized by [[Arduino]] project. This page deals with 8-bit series of these MCUs.

== Toolchain ==

Install {{Pkg|avr-gcc}} to get toolchain and GNU compiler.

== Programmers ==
To flash compiled firmware to the AVR chip you will need programmer and software to rule it. Most popular programmers are [https://www.fischl.de/usbasp USBasp], [https://www.microchip.com/DevelopmentTools/ProductDetails/PartNO/ATAVRISP2 AVRISP mkII], [https://www.microchip.com/DevelopmentTools/ProductDetails/ATATMEL-ICE Atmel-ICE] and [https://www.microchip.com/DevelopmentTools/ProductDetails/PartNO/ATSTK500 STK500]. [https://www.olimex.com/Products/AVR/Programmers/AVR-PG2B There is] also exists the simplest DIY-programmer which works with LPT port. {{Pkg|avrdude}} supports them all great.

=== udev issues ===

If you're using AVRISP mkII or USBasp programmers please consider installing {{AUR|avrisp-udev}} and/or {{AUR|usbasp-udev}} respectively to be able to run avrdude without superuser rights.

== Usage ==

To compile C program for AVR chip (let's consider ATmega8A running at 8 MHz as example) you can use {{ic|avr-gcc}} directly. You should only specify target MCU (full list of supported MCUs could be found in avr-gcc man page) and it's working frequency:

 $ avr-gcc -DF_CPU=8000000UL -mmcu=atmega8a -std=gnu99 main.c -o main.elf

avrdude is smart enough to work with the resulting ELF file but you can convert it explicitly to Intel HEX:

 $ avr-objcopy -O ihex -j .text -j .data main.elf main.hex

Then run avrdude and specify flash ROM as destination for formware burning (in this example AVRISP mkII is used and clock speed is lowered to the 125 kHz to be on safe side):

 $ avrdude -p atmega8 -c avrispmkII -B 125kHz -U flash:w:main.hex

That's all. Among other things avrdude can work with EEPROM memory, fuse and lock bits. For example, to set up low and high fuses to the 0x9F and 0xD1 respectively use the following incantation:

 $ avrdude -p atmega8 -c avrispmkII -B 125kHz -U lfuse:w:0x9F:m -U hfuse:w:0xD1:m

Just remember that ISP programming speed shouldn't exceed 1/8 of MCU's working frequency. A lot of new chips comes with 1 MHz speed settings so using 125 kHz as starting value should be fine enough.

== Tips and tricks ==

=== Optimization ===

Because AVRs come with tight flash ROM size and relatively weak CPUs you can consider some optimizations to improve space usage and overall performance of your device. It's common practice to enable GCC optimization level {{ic|-Os}} and turn on some extra features: {{ic|-funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums}}. To exclude unnecessary library references perform garbage collection: {{ic|-ffunction-sections -fdata-sections -Wl,--gc-sections}}.

=== Sample Makefile ===

Managing huge project could be tedious and Makefile workflow is the most efficient way to deal with it. Here are sample Makefile based on [https://www.avrfreaks.net/sites/default/files/Makefile.txt AVRfreaks] version:

 CC = avr-gcc
 OBJCOPY = avr-objcopy
 SIZE = avr-size
 NM = avr-nm
 AVRDUDE = avrdude
 REMOVE = rm -f
 
 MCU = atmega8a
 F_CPU = 8000000
 
 LFUSE = 0x9f
 HFUSE = 0xd1
 
 TARGET = firmware
 SRC = main.c lcd.c twi.c
 OBJ = $(SRC:.c=.o)
 LST = $(SRC:.c=.lst)
 
 FORMAT = ihex
 
 OPTLEVEL = s
 
 CDEFS = 
 
 CFLAGS = -DF_CPU=$(F_CPU)UL
 CFLAGS += $(CDEFS)
 CFLAGS += -O$(OPTLEVEL)
 CFLAGS += -mmcu=$(MCU)
 CFLAGS += -std=gnu99
 CFLAGS += -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums
 CFLAGS += -ffunction-sections -fdata-sections
 CFLAGS += -Wall -Wstrict-prototypes
 CFLAGS += -Wa,-adhlns=$(<:.c=.lst)
 
 LDFLAGS = -Wl,--gc-sections
 LDFLAGS += -Wl,--print-gc-sections
 
 AVRDUDE_MCU = atmega8
 AVRDUDE_PROGRAMMER = avrispmkII
 AVRDUDE_SPEED = -B 1MHz
 
 AVRDUDE_FLAGS = -p $(AVRDUDE_MCU)
 AVRDUDE_FLAGS += -c $(AVRDUDE_PROGRAMMER)
 AVRDUDE_FLAGS += $(AVRDUDE_SPEED)
 
 MSG_LINKING = Linking:
 MSG_COMPILING = Compiling:
 MSG_FLASH = Preparing HEX file:
 
 all: gccversion $(TARGET).elf $(TARGET).hex size
 
 .SECONDARY: $(TARGET).elf
 .PRECIOUS: $(OBJ)
 
 %.hex: %.elf
         @echo
         @echo $(MSG_FLASH) $@
         $(OBJCOPY) -O $(FORMAT) -j .text -j .data $< $@
 
 %.elf: $(OBJ)
         @echo
         @echo $(MSG_LINKING) $@
         $(CC) -mmcu=$(MCU) $(LDFLAGS) $^ --output $(@F)
 
 %.o : %.c
         @echo $(MSG_COMPILING) $<
         $(CC) $(CFLAGS) -c $< -o $(@F)
 
 gccversion:
         @$(CC) --version
 
 size: $(TARGET).elf
         @echo
         $(SIZE) -C --mcu=$(AVRDUDE_MCU) $(TARGET).elf
 
 analyze: $(TARGET).elf
         $(NM) -S --size-sort -t decimal $(TARGET).elf
 
 isp: $(TARGET).hex
         $(AVRDUDE) $(AVRDUDE_FLAGS) -U flash:w:$(TARGET).hex
 
 fuses:
         $(AVRDUDE) $(AVRDUDE_FLAGS) -U lfuse:w:$(LFUSE):m -U hfuse:w:$(HFUSE):m
 
 release: fuses isp
 
 clean:
         $(REMOVE) $(TARGET).hex $(TARGET).elf $(OBJ) $(LST) *~

=== Calculating control register values ===

To speed up development of your projects you can use {{AUR|avrcalc}} utility which helps to calculate different parameters for control registers regarding timers, frequencies etc.

== See also ==
* [[Arduino]]
* https://www.microchip.com/design-centers/8-bit/avr-mcus