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/*
* baudcheck.c
* Mar, 2013 by Bill Westfield (WestfW@yahoo.com)
* Exercises in executing arithmetic code on a system that we can't count
* on having the usual languages or tools installed.
*
* This little "C program" is run through the C preprocessor using the same
* arguments as our "real" target (which should assure that it gets the
* same values for clock speed and desired baud rate), and produces as
* output a shell script that can be run through bash, and THAT in turn
* writes the desired output...
*
* Note that the C-style comments are stripped by the C preprocessor.
*/
/*
* First strip any trailing "L" from the defined constants. To do this
* we need to make the constants into shell variables first.
*/
bpsx=BAUD_RATE
bps=${bpsx/L/}
fcpux=F_CPU
fcpu=${fcpux/L/}
// echo f_cpu = $fcpu, baud = $bps
/*
* Compute the divisor
*/
BAUD_SETTING=$(( ( ($fcpu + $bps * 4) / (($bps * 8))) - 1 ))
// echo baud setting = $BAUD_SETTING
/*
* Based on the computer divisor, calculate the actual bitrate,
* And the error. Since we're all integers, we have to calculate
* the tenths part of the error separately.
*/
BAUD_ACTUAL=$(( ($fcpu/(8 * (($BAUD_SETTING)+1))) ))
BAUD_ERROR=$(( (( 100*($bps - $BAUD_ACTUAL) ) / $bps) ))
ERR_TS=$(( ((( 1000*($bps - $BAUD_ACTUAL) ) / $bps) - $BAUD_ERROR * 10) ))
ERR_TENTHS=$(( ERR_TS > 0 ? ERR_TS: -ERR_TS ))
/*
* Print a nice message containing the info we've calculated
*/
echo BAUD RATE CHECK: Desired: $bps, Real: $BAUD_ACTUAL, UBRRL = $BAUD_SETTING, Error=$BAUD_ERROR.$ERR_TENTHS\%
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