| Title |
Toggle the DTR and RTS lines on a serial port from a C program |
| Ref. No. |
QNX.000009291 |
| Category(ies) |
Character I/O |
| Issue |
Using a C function, we'd like to toggle the DTR and RTS lines on our serial port. Problem is, we can't seem to find a way to do this. Can we actually toggle these from within a program?
|
| Solution |
The function qnx_ioctl() will accomplish this. To see which serial lines can be toggled by this function, look at /usr/include/sys/qioctl.h. Some serial lines are read-only, which means that only the retrieve status information may be read. RTS and DTR, however, are both read/write, so they are free to be toggled.
Here's an example of how to raise and lower these lines:
#include <sys/types.h>
#include <sys/qioctl.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#define SERDEV1 "/dev/serl"
main(){
x09int file_des;
x09long oldbits,newbits[2]={0,0};
x09if ((file_des = open (SERDEV1,0_RDWR))==-1){
x09x09printf("Unable to open %s:%s:,SERDEV1,sterror(errno));exit(1);
x09}
// The send buffer (newbits) consists of 8 bytes organized as two
// longs (bits,mask). The return buffer (oldbits) consist of 4 bytes.
//
// The ioctl returns the state of the device control bits as they
// were found BEFORE the call was made (oldbits). The device control bits
//are then modified using the rule:
// newbits = (oldbits & ~mask) | (bits & mask)
printf("Raising DTR and RTSn");
// From the qioctl.h header file we find that DTR is bit 0 and
// RTS is bit 1. WE want to raise RTS and DTR therefore the mask
// is 0x0003 and the bits will be 0x0003
x09newbits[0]=0x0003;
x09newbits[1]=0x0003;
x09if (qnx_ioctl(file_des, QCTL_DEV_CTL,&newbits, 8, &oldbits, 4)=-1)
x09x09printf("qnx_ioctl failed:%xn",strerror(errno));
// set mask to zero, we simply want to read the status of DTR and RTS
x09newbits[1]=0x0000;
x09if (qnx_ioctl(file_des,QCTL_DEV_CTL, &newbits, 8, &oldbits, 4)=-1)
x09x09printf("qnx_ioctl failed:%xn",strerror(errno));
x09printf("Serial State:");
x09printf("%cDTR", (oldbits & 0x0001L)?'+':'-');
x09printf("%cRTS", (oldbits & 0x0002L)?'+':'-');
x09printf("n");
printf("lowering DTR and RTSn");
// here we wish to lower DTR and RTS. We set up the
// mask to 0x0003 and set the bits to 0x0000
x09newbits[0]=0x0000;
x09newbits[1]=0x0003;
x09if (qnx_ioctl(file_des,QCTL_DEV_CTL,&newbits,8,&oldbits,4)=-1
x09x09printf(qnx_ioctl failed: "%sn", strerror(errno));
// again set mask to zero, we simply want to read the status of DTR and RTS
x09newbits[1]=0x0000;
x09if (qnx_ioctl(file_des,QCTL_DEV_CTL, &newbits, 8, &oldbits, 4)=-1)
x09x09printf("Serial State:");
x09printf("%cDTR", (oldbits & 0x0001L)? '+': '-');
x09printf("%cRTS", (oldbits & 0x0002L)? '+': '-');
x09printf("n");
x09close(file_des);
}
|
|
