[avr-libc-dev] [patch #5343] Add a util/setbaud.h "helper" file

[Carlos Lamas]

Follow-up Comment #3, patch #5343 (project avr-libc):

Hello,

There were overflow problems with baud rates lower than 32768 in C
expressions. I couldn't see the problem before because my F_CPU and BAUD were
defined long. This is solved in version 1.3 submitted by tacking UL at the end
of the constants involved to force the compiler to use long type arithmetics.
cpp expressions (#if's) are supposed to operate in 64 bit precision and they
shouldn't overflow for reasonable frequency and baud rate values.

The rounding errors were issued previously and they should not give different
results to hand calculated.

UBRR values delivered had the same error tolerance, 2% default. Obviously
when there was no overflow errors.

U2X=0 was always used when possible.

Anyway, I can't see advantages in using a "short" lookup table for this case
of so many possible F_CPU/BAUD combinations.

Carlos.

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Additional Item Attachment:

File name: setbaud.h                      Size:4 KB
V1.3 header to set UBRR from given F_CPU/BAUD values
<http://savannah.nongnu.org/patch/download.php?file_id=10659>

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