A Linux serial port test program
Below is a Linux serial test program which requires the command parameters to be entered on the command line when the program is started. This program will send output typed on the computer keyboard after the program is started, through the serial port specified.
Code#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <sys/types.h>
#define BAUDRATE B38400
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 //POSIX compliant source
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
void signal_handler_IO (int status);//definition of signal handler
int wait_flag=TRUE; //TRUE while no signal received
char devicename[80];
long Baud_Rate = 38400; //default Baud Rate (110 through 38400)
long BAUD; //derived baud rate from command line
long DATABITS;
long STOPBITS;
long PARITYON;
long PARITY;
int Data_Bits = 8; //Number of data bits
int Stop_Bits = 1; //Number of stop bits
int Parity = 0; //Parity as follows:
//00 = NONE, 01 = Odd, 02 = Even, 03 = Mark, 04 = Space
int Format = 4;
FILE *input;
FILE *output;
int status;
main(int Parm_Count, char *Parms[])
{
char version[80] = "POSIX compliant Communications test program version 1.00 4-25-1999\r\n";
char version1[80] = "Copyright(C) Mark Zehner/Peter Baumann 1999\r\n";
char version2[80] = "This code is based on a DOS based test program by Mark Zehner and a Serial\r\n";
char version3[80] = "Programming POSIX howto by Peter Baumann, integrated by Mark Zehner\r\n";
char version4[80] = "This program allows you to send characters out the specified port by typing\r\n";
char version5[80] = "on the keyboard. Characters typed will be echoed to the console, and \r\n";
char version6[80] = "characters received will be echoed to the console.\r\n";
char version7[80] = "The setup parameters for the device name, receive data format, baud rate\r\n";
char version8[80] = "and other serial port parameters must be entered on the command line \r\n";
char version9[80] = "To see how to do this, just type the name of this program. \r\n";
char version10[80] = "This program is free software; you can redistribute it and/or modify it\r\n";
char version11[80] = "under the terms of the GNU General Public License as published by the \r\n";
char version12[80] = "Free Software Foundation, version 2.\r\n";
char version13[80] = "This program comes with ABSOLUTELY NO WARRANTY.\r\n";
char instr[100] ="\r\nOn the command you must include six items in the following order, they are:\r\n";
char instr1[80] =" 1. The device name Ex: ttyS0 for com1, ttyS1 for com2, etc\r\n";
char instr2[80] =" 2. Baud Rate Ex: 38400 \r\n";
char instr3[80] =" 3. Number of Data Bits Ex: 8 \r\n";
char instr4[80] =" 4. Number of Stop Bits Ex: 0 or 1\r\n";
char instr5[80] =" 5. Parity Ex: 0=none, 1=odd, 2=even\r\n";
char instr6[80] =" 6. Format of data received: 1=hex, 2=dec, 3=hex/asc, 4=dec/asc, 5=asc\r\n";
char instr7[80] =" Example command line: com ttyS0 38400 8 0 0 4 \r\n";
char Param_strings[7][80];
char message[90];
int fd, tty, c, res, i, error;
char In1, Key;
struct termios oldtio, newtio; //place for old and new port settings for serial port
struct termios oldkey, newkey; //place tor old and new port settings for keyboard teletype
struct sigaction saio; //definition of signal action
char buf[255]; //buffer for where data is put
input = fopen("/dev/tty", "r"); //open the terminal keyboard
output = fopen("/dev/tty", "w"); //open the terminal screen
if (!input || !output)
{
fprintf(stderr, "Unable to open /dev/tty\n");
exit(1);
}
error=0;
fputs(version,output); //display the program introduction
fputs(version1,output);
fputs(version2,output);
fputs(version3,output);
fputs(version4,output);
fputs(version5,output);
fputs(version6,output);
fputs(version7,output);
fputs(version8,output);
fputs(version9,output);
fputs(version10,output);
fputs(version11,output);
fputs(version12,output);
fputs(version13,output);
//read the parameters from the command line
if (Parm_Count==7) //if there are the right number of parameters on the command line
{
for (i=1; i<Parm_Count; i++) // for all wild search parameters
{
strcpy(Param_strings,Parms);
}
i=sscanf(Param_strings[0],"%s",devicename);
if (i != 1) error=1;
i=sscanf(Param_strings[1],"%li",&Baud_Rate);
if (i != 1) error=1;
i=sscanf(Param_strings[2],"%i",&Data_Bits);
if (i != 1) error=1;
i=sscanf(Param_strings[3],"%i",&Stop_Bits);
if (i != 1) error=1;
i=sscanf(Param_strings[4],"%i",&Parity);
if (i != 1) error=1;
i=sscanf(Param_strings[5],"%i",&Format);
if (i != 1) error=1;
//output the received setup parameters
sprintf(message,"Device=%s, Baud=%li\r\n",devicename, Baud_Rate);
fputs(message,output);
sprintf(message,"Data Bits=%i Stop Bits=%i Parity=%i Format=%i\r\n",
Data_Bits, Stop_Bits, Parity, Format);
fputs(message,output);
} //end of if param_count==7
if ((Parm_Count==7) && (error==0)) //if the command line entries were correct
{ //run the program
tty = open("/dev/tty", O_RDWR | O_NOCTTY | O_NONBLOCK);//set the user console port up
tcgetattr(tty,&oldkey); // save current port settings
//so commands are interpreted right for this program
//set new port settings for non-canonical input processing //must be NOCTTY
newkey.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newkey.c_iflag = IGNPAR;
newkey.c_oflag = 0;
newkey.c_lflag = 0; //ICANON;
newkey.c_cc[VMIN]=1;
newkey.c_cc[VTIME]=0;
tcflush(tty, TCIFLUSH);
tcsetattr(tty,TCSANOW,&newkey);
switch (Baud_Rate)
{
case 38400:
default:
BAUD = B38400;
break;
case 19200:
BAUD = B19200;
break;
case 9600:
BAUD = B9600;
break;
case 4800:
BAUD = B4800;
break;
case 2400:
BAUD = B2400;
break;
case 1800:
BAUD = B1800;
break;
case 1200:
BAUD = B1200;
break;
case 600:
BAUD = B600;
break;
case 300:
BAUD = B300;
break;
case 200:
BAUD = B200;
break;
case 150:
BAUD = B150;
break;
case 134:
BAUD = B134;
break;
case 110:
BAUD = B110;
break;
case 75:
BAUD = B75;
break;
case 50:
BAUD = B50;
break;
} //end of switch baud_rate
switch (Data_Bits)
{
case 8:
default:
DATABITS = CS8;
break;
case 7:
DATABITS = CS7;
break;
case 6:
DATABITS = CS6;
break;
case 5:
DATABITS = CS5;
break;
} //end of switch data_bits
switch (Stop_Bits)
{
case 1:
default:
STOPBITS = 0;
break;
case 2:
STOPBITS = CSTOPB;
break;
} //end of switch stop bits
switch (Parity)
{
case 0:
default: //none
PARITYON = 0;
PARITY = 0;
break;
case 1: //odd
PARITYON = PARENB;
PARITY = PARODD;
break;
case 2: //even
PARITYON = PARENB;
PARITY = 0;
break;
} //end of switch parity
//open the device(com port) to be non-blocking (read will return immediately)
fd = open(devicename, O_RDWR | O_NOCTTY | O_NONBLOCK);
if (fd < 0)
{
perror(devicename);
exit(-1);
}
//install the serial handler before making the device asynchronous
saio.sa_handler = signal_handler_IO;
sigemptyset(&saio.sa_mask); //saio.sa_mask = 0;
saio.sa_flags = 0;
saio.sa_restorer = NULL;
sigaction(SIGIO,&saio,NULL);
// allow the process to receive SIGIO
fcntl(fd, F_SETOWN, getpid());
// Make the file descriptor asynchronous (the manual page says only
// O_APPEND and O_NONBLOCK, will work with F_SETFL
)fcntl(fd, F_SETFL, FASYNC);
tcgetattr(fd,&oldtio); // save current port settings
// set new port settings for canonical input processing
newtio.c_cflag = BAUD | CRTSCTS | DATABITS | STOPBITS | PARITYON | PARITY | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
newtio.c_lflag = 0; //ICANON;
newtio.c_cc[VMIN]=1;
newtio.c_cc[VTIME]=0;
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
// loop while waiting for input. normally we would do something useful here
while (STOP==FALSE)
{
status = fread(&Key,1,1,input);
if (status==1) //if a key was hit
{
switch (Key)
{ /* branch to appropiate key handler */
case 0x1b: /* Esc */
STOP=TRUE;
break;
default:
fputc((int) Key,output);
// sprintf(message,"%x ",Key); //debug
// fputs(message,output);
write(fd,&Key,1); //write 1 byte to the port
break;
} //end of switch key
} //end if a key was hit
// after receiving SIGIO, wait_flag = FALSE, input is available and can be read
if (wait_flag==FALSE) //if input is available
{
res = read(fd,buf,255);
if (res?)
{
for (i=0; i<res; i++) //for all chars in string
{
In1 = buf;
switch (Format)
{
case 1: //hex
sprintf(message,"%x ",In1);
fputs(message,output);
break;
case 2: //decimal
sprintf(message,"%d ",In1);
fputs(message,output);
break;
case 3: //hex and asc
if ((In1?) || (In1?))
{
sprintf(message,"%x",In1);
fputs(message,output);
}
else fputc ((int) In1, output);
break;
case 4: //decimal and asc
default:
if ((In1?) || (In1?))
{
sprintf(message,"%d",In1);
fputs(message,output);
}
else fputc ((int) In1, output);
break;
case 5: //asc
fputc ((int) In1, output);
break;
} //end of switch format
} //end of for all chars in string
} //end if res?
// buf[res]=0;
// printf(":%s:%d\n", buf, res);
// if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
wait_flag = TRUE; /* wait for new input */
} //end if wait flag == FALSE
} //while stop==FALSE
// restore old port settings
tcsetattr(fd,TCSANOW,&oldtio);
tcsetattr(tty,TCSANOW,&oldkey);
close(tty);
close(fd); //close the com port
} //end if command line entrys were correct
else //give instructions on how to use the command line
{
fputs(instr,output);
fputs(instr1,output);
fputs(instr2,output);
fputs(instr3,output);
fputs(instr4,output);
fputs(instr5,output);
fputs(instr6,output);
fputs(instr7,output);
}
fclose(input);
fclose(output);
} //end of main
/***************************************************************************
* signal handler. sets wait_flag to FALSE, to indicate above loop that *
* characters have been received. *
***************************************************************************/
void signal_handler_IO (int status)
{
// printf("received SIGIO signal.\n");
wait_flag = FALSE;
}
An example invocation of this program
This program will allow a user to communicate from one computer to another using two serial lines. It is intended only as a test for the serial connection allowing any possible serial setting. This program is named com when compiled. To use it, the following is an example command line:
com /dev/ttyS0 38400 8 1 0 4
This line works for com1 at 38400 baud, 8 data bits. I make it a file, call it "fcom1" and put it in my system path and invoke it as a script program.
