>> I am a newbie to the 7250 as well as to linux. I need to read a rs232
>> signal from my com2 port and have tried lots of code from online
>> guides with no sucess so I turned to this group and found this post
>> and have used the code displayed below. I have even commented out the
The program is not a good example because it is fundamentally broken.
The most serious problem is here:
>>>> int read_port(int file_id)
>>>> {
>>>> char buffer[512];
>>>> int count=0;
>>>> int lines = 0;
>>>>
>>>> while(lines < 50)
>>>> {
>>>> read(file_id, buffer, count);
Here, count=0 so it is asking to read zero bytes from the serial port.
Of course, if you ask for nothing, you will get nothing.
read() returns the number of bytes actually read, which is ignored
by this program.
It should say something like:
count = read( file_id, buffer, sizeof(buffer)-1 );
if (count < 0)
{ /* look at errno to see what error occured */ }
if (count == 0)
{ /* there were no bytes to read */ }
if (count > 0)
{ /* you can use the bytes in buffer */ }
I say sizeof(buffer)-1 so it asks for at most 511 bytes. That
way buffer[count]='\0' does not overflow the array if you get as
many bytes as you asked for.
It might be helpful to read some of the serial port tutorials on the web.
A brief search found a couple that don't look too bad:
http://www.faqs.org/docs/Linux-HOWTO/Serial-Programming-HOWTO.html
http://www.easysw.com/~mike/index.php?serial/serial.html+printable
Linux is POSIX compliant. If you need help with Linux programming,
just about any book about programming in C for POSIX, Unix or Linux
systems can be useful.
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