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POReading and writing binary data over serial port
 

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  1. POReading and writing binary data over serial port
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    <p>So I searched around, and couldn't exactly find what I needed. I need help reading and writing binary data over a serial port, and would appreciate any advice you may have. Please note, I asked a question similar to this earlier when I was at a different stage of this project.</p> <p>Below are programs. The first program opens a file "test.jpg", reads it in binary mode and stores the result in a buffer. It then closes the file, and is supposed to send that file over a serial port.</p> <p>The second program creates a file called "testout.jpg", and is supposed to read in the data sent from the previous program.</p> <p>I have a hunch that the problem in my code lies in the second program. Perhaps I need to use fread for that too? I tried, but I cannot figure out how to implement it for a serial port as I am relatively new to programming.</p> <p>Many thanks for your time.</p> <p>Serial write:</p> <pre><code> #include &lt;stdio.h&gt; /* Standard input/output definitions */ #include &lt;string.h&gt; /* String function definitions */ #include &lt;unistd.h&gt; /* UNIX standard function definitions */ #include &lt;fcntl.h&gt; /* File control definitions */ #include &lt;errno.h&gt; /* Error number definitions */ #include &lt;termios.h&gt; /* POSIX terminal control definitions */ #include &lt;stdlib.h&gt; int main() { //writing int writeport = open_port("/dev/ttyUSB0"); //open file FILE *file; char *buffer; int fileLen; file = fopen("test.jpg", "rb"); //get file size fseek(file, 0, SEEK_END); fileLen = ftell(file); fseek(file, 0, SEEK_SET); buffer = (char *)malloc(fileLen + 1); //read file contents fread(buffer, fileLen, 1, file); fclose(file); int n = write(writeport, buffer, fileLen + 1); if (n &lt; 0) fputs("write() of bytes failed!\n", stderr); //closing ports close(writeport); } int open_port(char str[]) { int fd = open(str, O_RDWR | O_NOCTTY | O_NONBLOCK); // ?? NDELAY or NONBLOCK? if (fd == -1) { perror("open_port: Unable to open /dev/ttyS0 - "); } else fcntl(fd, F_SETFL, 0); struct termios options; tcgetattr(fd, &amp;options); //this gets the current options set for the port // setting the options cfsetispeed(&amp;options, B9600); //input baudrate cfsetospeed(&amp;options, B9600); // output baudrate options.c_cflag |= (CLOCAL | CREAD); // ?? enable receicer and set local mode //options.c_cflag &amp;= ~CSIZE; /* mask the character size bits */ options.c_cflag |= CS8; /* select 8 data bits */ options.c_lflag &amp;= ~(ICANON | ECHO | ECHOE | ISIG); // choosing raw input options.c_iflag &amp;= ~INPCK; // disable parity check options.c_iflag &amp;= ~(IXON | IXOFF | IXANY); // disable software flow control options.c_oflag |= OPOST; // ?? choosing processed output options.c_cc[VMIN] = 0; // Wait until x bytes read (blocks!) options.c_cc[VTIME] = 0; // Wait x * 0.1s for input (unblocks!) // settings for no parity bit options.c_cflag &amp;= ~PARENB; options.c_cflag &amp;= ~CSTOPB; options.c_cflag &amp;= ~CSIZE; options.c_cflag |= CS8; tcsetattr(fd, TCSANOW, &amp;options); //set the new options ... TCSANOW specifies all option changes to occur immediately return (fd); } </code></pre> <p>Serial read:</p> <pre><code> #include &lt;stdio.h&gt; /* Standard input/output definitions */ #include &lt;string.h&gt; /* String function definitions */ #include &lt;unistd.h&gt; /* UNIX standard function definitions */ #include &lt;fcntl.h&gt; /* File control definitions */ #include &lt;errno.h&gt; /* Error number definitions */ #include &lt;termios.h&gt; /* POSIX terminal control definitions */ int main() { //reading int readport = open_port("/dev/ttyUSB1"); //open resultant file FILE *file; //system("rm testout.jpg"); file = fopen("testout.jpg", "wb"); //trying to read one character at a time char buff; int n = 1; while (n &gt; 0) { n = read(readport, &amp;buff, 1); //printf("%c", buff, buff); **//I tried these three methods, with little success** //fprintf(file, "%c", buff); //fwrite(&amp;buff, 1, 1, file); //write(file, &amp;buff, 1); } //closing ports close(readport); fclose(file); } int open_port(char str[]) { int fd = open(str, O_RDWR | O_NOCTTY | O_NONBLOCK); // ?? NDELAY or NONBLOCK? if (fd == -1) { perror("open_port: Unable to open /dev/ttyS0 - "); } else fcntl(fd, F_SETFL, 0); struct termios options; tcgetattr(fd, &amp;options); //this gets the current options set for the port // setting the options cfsetispeed(&amp;options, B9600); //input baudrate cfsetospeed(&amp;options, B9600); // output baudrate options.c_cflag |= (CLOCAL | CREAD); // ?? enable receicer and set local mode //options.c_cflag &amp;= ~CSIZE; /* mask the character size bits */ options.c_cflag |= CS8; /* select 8 data bits */ options.c_lflag &amp;= ~(ICANON | ECHO | ECHOE | ISIG); // choosing raw input options.c_iflag &amp;= ~INPCK; // disable parity check options.c_iflag &amp;= ~(IXON | IXOFF | IXANY); // disable software flow control options.c_oflag |= OPOST; // ?? choosing processed output options.c_cc[VMIN] = 0; // Wait until x bytes read (blocks!) options.c_cc[VTIME] = 0; // Wait x * 0.1s for input (unblocks!) // settings for no parity bit options.c_cflag &amp;= ~PARENB; options.c_cflag &amp;= ~CSTOPB; options.c_cflag &amp;= ~CSIZE; options.c_cflag |= CS8; tcsetattr(fd, TCSANOW, &amp;options); //set the new options ... TCSANOW specifies all option changes to occur immediately return (fd); } </code></pre>
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    1. COYou don't seem to have any error handling, Have you removed it to reduce the amount of code we need to read to understand your problem or do you simply not have it in your code (in which case you should at least check the the files/ports you open are valid and in good state!). The use of `O_NONBLOCK` suggests that you are not waiting for the port to be open (or am I reading it wrong?).
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    2. CO`while (n > 0) { n = read(readport, &buff, 1); ` is wromg. Test the n immediately after the read(), and break out of the loop if (n <= 0). (n==0 is special: depends on blocking/non blocking)
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    3. CO@YePhlck Yes you are right about both those things. O_NONBLOCK was used because it wasn't working with NDELAY.
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