AVR Freaks

My 328PB datasheet circa 2015 did not specify the CFD fuse.

The 2017 datasheet does document the CFD fuse

My Arduino v1.8.9 avrdude.conf does not accept writing to bit#3 of EFUSE.

I have no idea what avrdude.conf you might be using.

It is simple enough to see the "m328"  section e.g.

    memory "efuse"
	size = 1;
	min_write_delay = 4500;
	max_write_delay = 4500;
	read = "0 1 0 1 0 0 0 0 0 0 0 0 1 0 0 0",
	       "x x x x x x x x o o o o o o o o";

	write = "1 0 1 0 1 1 0 0 1 0 1 0 0 1 0 0",
	      	"x x x x x x x x x x x x x i i i";
    ;

If you want to use avrdude to program CFD,  you need to enable bit #3 for write

This might cause problems with "other" devices that use "m328 parent" e.g. that do not use bit#3

So you should really create a custom "parent"

The real mystery is WHY.

Surely it is unwise to disable the CFD mechanism via the fuse.  i.e. CFD=0

The factory default is to enable CFD i.e. CFD=1

It seems an inappropriate name.   CFD implies Clock Failure Detect.

A fuse called CFD implies Clock Failure Disable

CFDDISABLE would be better

David.

From your link:

        write = "1 0 1 0 1 1 0 0 1 0 1 0 0 1 0 0",
 	        "x x x x x x x x x x x x x i i i";

So bit#3 has never been made "write"

I can only assume that someone had made bit#3 = 0 by mistake.

And the OP wants to restore it to the Factory default. i.e. bit#3 = 1

Personally,  I would just use atprogram.exe or AS7.0 to restore the EFUSE

And leave avrdude.conf as it is.

David.