Arduino compiler nonsense

By | March 27, 2013

I have spent a few hours investigating where all the RAM has gone in my new Arduino project. I need to investigate newer versions (still running 1.0), I really hope there are improvements.

My favorite WTFs:

  1. string constants are stored in RAM
  2. string constants can be stored in Flash. For that you need to wrap them in F(“blah”) macro.
  3. when using F(), the string is wrapped into an object and is no longer a char*. You can no longer pass such strings into functions expecting a const char*. Therefore only useless constants can be off-loaded to Flash
  4. no warning is given when the precious RAM is wasted
  5. no warning is given when RAM usage reaches 100%. Only Flash consumption is shown

Check out more info at

Here are a couple of useful commands that give RAM usage and allocation listing. Let’s say Arduino is installed at ~/arduino. First you need to enable verbose output during compilation in the Arduino IDE preferences. When compilation is done, find and replace my /tmp/build582139005597328143.tmp with your compilation directory found in the messages. Replace the Atmega model if necessary

~/arduino/hardware/tools/avr/bin$ avr-objdump -t -j .bss /tmp/build582139005597328143.tmp/controller.cpp.elf
/tmp/build582139005597328143.tmp/controller.cpp.elf:     file format elf32-avr

008003c8 l    d  .bss    00000000 .bss
0080041e l     O .bss    00000001 timer0_fract
00800416 g     O .bss    00000004 timer0_overflow_count
0080041a g     O .bss    00000004 timer0_millis
00800406 g     O .bss    00000008 keyCounters
008004c6 g       .bss    00000000 __bss_end
008003c8 g     O .bss    0000003e SCmd
0080041f g     O .bss    00000044 rx_buffer
00800463 g     O .bss    00000044 tx_buffer
008004a7 g     O .bss    0000001f Serial
008003c8 g       .bss    00000000 __bss_start
0080040e g     O .bss    00000008 startup_values

~/arduino/hardware/tools/avr/bin$ avr-size /tmp/build582139005597328143.tmp/controller.cpp.elf -C --mcu=atmega168p

AVR Memory Usage
Device: atmega168p

Program:    5992 bytes (36.6% Full)
(.text + .data + .bootloader)

Data:        358 bytes (35.0% Full)
(.data + .bss + .noinit)

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