AVR-Chat

The gcc compiler generates three distinct sections for RAM-based data 
whose names are .noinit, .bss and .data.  The .noinit section is for 
uninitialized data items.  The .bss section is for zero-initialized 
data items (BSS stands for Block Started by Symbol, a throwback to 
FORTRAN or even earlier days).  The .data section is for data items 
with non-zero initialization values.

After setting up the stack pointer (usually to the end of internal 
RAM), zeroes out the .bss section.  For the .data section, it copies a 
block of data from Flash (containing the initialization data) to the 
RAM section.  It does nothing at all to the .init section.

If needed, there is a means to inject code into various places of the 
startup sequence.  See the discussion of the .initN sections for more 
details.  In particular, see
http://www.nongnu.org/avr-libc/user-manual/mem_sections.html

Don Kinzer
ZBasic Microcontrollers
http://www.zbasic.net