Re: [avr-chat] F_CPU values for Atmega 169 (Butterfly board)

[Robert L Cochran]

Preston Wilson wrote:
> "Robert L Cochran" wrote:
>
>   
>> address@hidden butterfly]$ avr-gcc -I. -I/usr/avr/include -std=c99 -g
>> -mmcu=atmega169 -Os -fpack-struct -fshort-enums -funsigned-bitfields
>> -funsigned-char -Wall -Wstrict-prototypes -Wa,-ahlms=blinky.lst -c
>> blinky.c -o blinky.o
>> In file included from blinky.c:4:
>> /usr/lib/gcc/avr/4.1.2/../../../../avr/include/util/delay.h:84:3:
>> warning: #warning "F_CPU not defined for <util/delay.h>"
>>
>> What values for F_CPU do I need?
>>     
>
> The Butterfly is setup to run on the internal oscillator, which can run up
> to 8MHz (depends upon the voltage supplied to the part), and the way it is
> shipped, it is configured with the clock prescale set to 8, so that results
> in a 1MHz clock.  If you have not modified the CKSEL and CKDIV8 fuses, and
> you do not mess with the clock prescaler register(s) in your code, then that
> is what you are working with, and you need to set F_CPU to 1000000 (or
> 1MHz).
>
> Look at the section on system clock source in the datasheet for the
> ATmega169 where it describes all of the fuse and register settings that
> impact the part.
>
> -Preston
>
>
>   
Thank you! This is the first time I've really tried programming the
Butterfly outside of WinAVR. I need to spend some time with the
datasheet. I've also learned to add -std=c99 to my avr-gcc incantation
or it will complain about (for int i = 1...) loops.

Bob Cochran

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