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[on:]

I am making up a low power, minimalist board with an Atmega328P.
I will program it using an AVRISPmkII and therefore want to do away with the bootloader.

However when I look at the fuse settings (BOOTSZ) I see that there are only four options for bootloader size, ranging from 256 words to 2048 words.
i.e. there is no option for zero bootloader size.

As I am not using a bootloader, I want to free up this space for use by my sketch.

Can I use this address space or am I stuck with this 'black hole'?

[Reply #1 on:]

the boot size bits do not have any effect if the boot reset vector bit is not enabled, so don't worry about it. that space is available for use if boot reset vector bit is disabled

[Reply #2 on:]

Thanks Frank,

I sort of thought that that may be the case however the various fuse calculators (on the web) that I tried made no changes to the BOOTSZ options whether BOOTRST was set or not.

Cheers!

[Reply #3 on:]

I am the author of one of those calculators http://frank.circleofcurrent.com/fusecalc/, those options are text extracted from a XML file provided by Atmel.

Given a set of BOOTSZ bits, my code matches it up with one of the strings from the XML file. Hence, it is not smart enough to say "0 sized bootloader" when BOOTRST is disabled because each possible combination of BOOTSZ bits matches to only one string.

Besides, BOOTSZ does not matter if BOOTRST is disabled.

[Reply #4 on:]

Besides, BOOTSZ does not matter if BOOTRST is disabled.

As I suspected but when I looked at an online fuse calculator I expected the BOOTSZ options to be 'greyed out' when BOOTRST is disabled; but it wasn't.

Assuming that the calculator may have a bug in it I tried a different calculator. Sames result.
Having tried a few calculators, written by people with more knowledge than myself, I started to doubt my premise (outlined in your quote above).

Thats when I made this post. An easy conclusion to come to for a relative noob like me.

[Reply #5 on:]

I expected the BOOTSZ options to be 'greyed out' when BOOTRST is disabled; but it wasn't.

There is a good reason for that: Because everything is extracted from the XML, and nothing in the XML makes a relationship between BOOTSZ and BOOTRST. The code isn't as smart as a human who would make any relationship between the two.