The “real size” of hex file for AVR microcontroller

ROBIN DONG 2021-07-08 18:35

Recently I dug out myUSBasptool and a fewAVRmicrocontrollers, for enjoying programming the C language again. Unexpectedly, the oldATTINY2313VandATmega88Vcouldn’t work with my USBasp tool (maybe they have already been fused with an external crystal but I don’t have one at hand). The only two pieces that could work areATmega16AandATmega16L. At least I could still have some fun with it.

My waterfall-light built from ATmega16A

The code for playing the ATmega16A is at

Later when glancing over the documents of Atmel’s new ATTINY series, I found out that theATTINY13Aonly have 1KB space to store program. Myexampleof waterfall light was compiled out to a 2KB hex file. Does that mean I couldn’t put my program into the ATTINY13A? How could I get the real occupation size of flash for the hex file?

Here is one solution by usingavr-size

$ avr-size main.hex
   text	   data	    bss	    dec	    hex	filename
      0	    756	      0	    756	    2f4	main.hex

Only 756 bytes (text + data) will be used in flash, so the ATTINY13A should be okay.

Another command for this is more human-readable

$ avr-size --format=avr --mcu=atmega16 main.elf
AVR Memory Usage
Device: atmega16

Program:     756 bytes (4.6% Full)
(.text + .data + .bootloader)

Data:          6 bytes (0.6% Full)
(.data + .bss + .noinit)

Now, what should I do if I want to reduce the size of the binary file compiled from my code? Here is theguidefrom Atmel.

First, I change the type of the variable “mode” from “unsigned int” to “unsigned char”, this leads the binary file to 726 bytes. Then change all inner functions to “static” (I guess this removed some unused symbol for external linking), reduce the binary size to 668 bytes.

—— 2021.07.13 ——

Furthermore, when I use “-mrelax” option in gcc-avr forlinker relaxation, the binary size shrink to 656 bytes.

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