[avr-libc-dev] Fuse and lock bits

[Rick Altherr]

Having had a bit of experience with the CONFIG bits in PIC  
development, I was surprised to see that the FUSE and LOCK bits in  
AVR weren't able to be set in the source code.  A friend and I came  
up with the following solution:
- Create a header file for each device that contain:
  - A define that allocates an extra ELF section for the various  
fuse and lock bits
  - A set of defines that describe the various bits in the fuse and  
lock bits
  - A define for the default value described in the datasheet
- A set of Makefile rules that:
  - Extract the new ELF sections into separate hex files
  - Invoke avrdude with commands that program the lock and fuse bits  
with the contents of the new sections

Here is an excerpt from the ATmega8's header file for HFUSE:

/* High Fuse Byte */
#define HFUSE const unsigned char hfuse __attribute__((section  
(".hfuse")))

#define BOOTRST         ~_BV(0)
#define BOOTSZ0         ~_BV(1)
#define BOOTSZ1         ~_BV(2)
#define EESAVE          ~_BV(3)
#define CKOPT           ~_BV(4)
#define SPIEN           ~_BV(5)
#define WDTON           ~_BV(6)
#define RSTDISBL        ~_BV(7)

#define HFUSE_DEFAULT SPIEN & BOOTSZ1 & BOOTSZ0


The Makefile rules are a bit more complex since they are entwined  
with a whole set of rules to reduce the amount of setup needed for an  
AVR-based project.  I've attached an example project that shows these  
header files and Makefile rules in use.  The use of the fuse header  
is in example.c where LFUSE is set.  To build it, put the files from  
the header.tar.gz into the same directory as the I/O definition  
headers.  Then, in example.tar.gz, run 'make' to build the software  
and 'make program' to write it to a device.  To get rid of all the  
generated files, run 'make clean'.

headers.tar.gz
Description: GNU Zip compressed data

example.tar.gz
Description: GNU Zip compressed data

Currently, we only have files for the ATmega8 and ATmega16.  That's  
mainly because those are the only 2 devices we have used this with.   
It definitely makes keeping track of things like clock configuration  
and watchdog timer enable easier as well as enables a way for them to  
be included in a source repository.

--
Rick Altherr
address@hidden

"He said he hadn't had a byte in three days. I had a short, so I  
split it with him."
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