216 lines
4.9 KiB
C
216 lines
4.9 KiB
C
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#include "windows.h"
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#include <stdio.h>
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BOOL
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SerialGetDivisorFromBaud(
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IN ULONG ClockRate,
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IN LONG DesiredBaud,
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OUT PSHORT AppropriateDivisor
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)
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/*++
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Routine Description:
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This routine will determine a divisor based on an unvalidated
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baud rate.
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Arguments:
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ClockRate - The clock input to the controller.
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DesiredBaud - The baud rate for whose divisor we seek.
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AppropriateDivisor - Given that the DesiredBaud is valid, the
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LONG pointed to by this parameter will be set to the appropriate
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value. NOTE: The long is undefined if the DesiredBaud is not
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supported.
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Return Value:
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This function will return STATUS_SUCCESS if the baud is supported.
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If the value is not supported it will return a status such that
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NT_ERROR(Status) == FALSE.
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--*/
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{
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signed short calculatedDivisor;
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unsigned long denominator;
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unsigned long remainder;
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//
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// Allow up to a 1 percent error
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//
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unsigned long maxRemain18 = 18432;
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unsigned long maxRemain30 = 30720;
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unsigned long maxRemain42 = 42336;
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unsigned long maxRemain80 = 80000;
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unsigned long maxRemain;
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//
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// Reject any non-positive bauds.
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//
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denominator = DesiredBaud*(unsigned long)16;
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if (DesiredBaud <= 0) {
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*AppropriateDivisor = -1;
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} else if ((signed long)denominator < DesiredBaud) {
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//
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// If the desired baud was so huge that it cause the denominator
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// calculation to wrap, don't support it.
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//
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*AppropriateDivisor = -1;
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printf("baud to big\n");
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} else {
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if (ClockRate == 1843200) {
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maxRemain = maxRemain18;
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} else if (ClockRate == 3072000) {
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maxRemain = maxRemain30;
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} else if (ClockRate == 4233600) {
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maxRemain = maxRemain42;
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} else {
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maxRemain = maxRemain80;
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}
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calculatedDivisor = (signed short)(ClockRate / denominator);
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remainder = ClockRate % denominator;
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//
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// Round up.
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//
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if (((remainder*2) > ClockRate) && (DesiredBaud != 110)) {
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calculatedDivisor++;
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}
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//
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// Only let the remainder calculations effect us if
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// the baud rate is > 9600.
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//
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if (DesiredBaud >= 9600) {
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//
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// If the remainder is less than the maximum remainder (wrt
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// the ClockRate) or the remainder + the maximum remainder is
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// greater than or equal to the ClockRate then assume that the
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// baud is ok.
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//
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if ((remainder >= maxRemain) && ((remainder+maxRemain) < ClockRate)) {
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printf("remainder: %d\n",remainder);
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printf("error is: %f\n",((double)remainder)/((double)ClockRate));
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calculatedDivisor = -1;
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}
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}
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//
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// Don't support a baud that causes the denominator to
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// be larger than the clock.
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//
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if (denominator > ClockRate) {
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calculatedDivisor = -1;
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}
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//
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// Ok, Now do some special casing so that things can actually continue
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// working on all platforms.
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//
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if (ClockRate == 1843200) {
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if (DesiredBaud == 56000) {
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calculatedDivisor = 2;
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}
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} else if (ClockRate == 3072000) {
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if (DesiredBaud == 14400) {
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calculatedDivisor = 13;
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}
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} else if (ClockRate == 4233600) {
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if (DesiredBaud == 9600) {
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calculatedDivisor = 28;
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} else if (DesiredBaud == 14400) {
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calculatedDivisor = 18;
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} else if (DesiredBaud == 19200) {
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calculatedDivisor = 14;
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} else if (DesiredBaud == 38400) {
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calculatedDivisor = 7;
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} else if (DesiredBaud == 56000) {
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calculatedDivisor = 5;
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}
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} else if (ClockRate == 8000000) {
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if (DesiredBaud == 14400) {
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calculatedDivisor = 35;
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} else if (DesiredBaud == 56000) {
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calculatedDivisor = 9;
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}
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}
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*AppropriateDivisor = calculatedDivisor;
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}
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if (*AppropriateDivisor == -1) {
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return FALSE;
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}
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return TRUE;
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}
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void main(int argc,char *argv[]){
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unsigned long baudrate;
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signed short divisor = -1;
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if (argc > 1) {
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sscanf(argv[1],"%d",&baudrate);
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}
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if (!SerialGetDivisorFromBaud(
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1843200,
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baudrate,
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&divisor
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)) {
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printf("Couldn't get a divisor\n");
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} else {
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printf("Divisor is: %d\n",divisor);
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}
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}
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