Linux Programming Discussions

[Trevor Saunders]

Hi,

> { /*Receive incoming serial data.*/
>  STOP=FALSE;                                         
> res = 0; /*eventually shows where buffer ends*/
> sleep(1);
> /*Force a wait to cause receive buffer to stabilize.*/
>         while (STOP==FALSE) {       /* loop for input */                      
>   
>           res = read(fd,buf,sizeof(buf));   /* returns after sizeof(buf) chars have been inputed or timeoutt */ 
>   
>   
> STOP=TRUE;                                         
>         }                                                                     
>           buf[res]=NULL;               /* so we can printf... */                 

that looks suspect to me, I forget what the spec says NULL means in that
case, but I'd use '\0' or just 0 instead, but what you do may work.  I
also suspect that if read reads sizeof(buf) bytes and then you set
buf[sizeof(buf)] = 0 you will possibly touch memory that isn't yours.

Trev


> /*That makes sure there is a null to form a strint.*/
> /*printf("%s\n", buf);                                       */
> return;
> } /*Receive incoming serial data.*/
> 
> 	The only thing I can adjust in the port setup is a
> variable that is either kept at 0 so it will time out if no
> characters are received at all or to, say, 1024 or whatever the
> buffer is defined as. This really doesn't effect the issue but
> if set to > 0, the timeout never happens until at least one
> character is received.
> 
> 	Here is the initialization routine. Hardware flow
> control is not an option as the receiver does not recognize
> RTS/CTS. 
> 
> #include "headers.h"
> #include "defs.h"
> #include "externs.h"
>   
>   
> void portinit()
>       {                                                                       
>         struct termios oldtio,newtio;                                         
>   
>         fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );                           
>   
>         if (fd <0) {perror(MODEMDEVICE); exit(-1); }                          
>   
>         tcgetattr(fd,&oldtio); /* save current port settings */               
> 
> /*Clear everything about that port.*/
>         bzero(&newtio, sizeof(newtio));                                       
>   
>         newtio.c_cflag = BAUDRATE | CS8 | CLOCAL | CREAD;           
>   
>         newtio.c_iflag = IGNPAR | ICRNL;
>   
>         newtio.c_oflag &= ~OPOST;
>   
>   
>         /* set input mode (non-canonical, no echo,...) */                     
>   
>         newtio.c_lflag = 0;                                                   
>   
>         newtio.c_cc[VTIME]    = 20;   /* inter-character timer .1 seconds/tick */       
>         newtio.c_cc[VMIN] = 0; /*Blocks until VMIN chars or timeout.*/ 
>                                                                               
>   
>         tcflush(fd, TCIFLUSH);                                                
>   
>         tcsetattr(fd,TCSANOW,&newtio);                                        
>   
> return;
>       }                                                                       
> 
> I have tried tcflush at the end of a receive with absolutely no
> effect on anything.
> Shane W writes:
> > Hmm, reading from the ttySx device should never give
> > duplicatedcharacters so it sounds like something is up with
> > your buffer. I wouldn't zero it out but just keep note of
> > the number of bytes read and when to stop. Also, after your
> > first read returns, don't sleep but rather call poll() on
> > the device which will return when there is data ready to be
> > read.
> 
> 	Yes. It is like it is already ready to receive data too
> early.
> 
> 	The hardware is a USB-based 8-port adaptor which behaves
> quite normally when using Kermit or other serial routines.
> 
> 	Thanks.
> 
> _______________________________________________
> Blinux-list mailing list
> Blinux-list at redhat.com
> https://www.redhat.com/mailman/listinfo/blinux-list
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: Digital signature
URL: <http://listman.redhat.com/archives/blinux-list/attachments/20100831/3d5af966/attachment.sig>