Hello list
I have a RS485 device connect to a PC serial port. To handle half duplex
transmision I must activate/deactivate RTS line. I think this is a very
common practice.To do this I have these functions
int set_to_write( int _port)
{
int nStatus;
if ( ioctl( _port, TIOCMGET, &nStatus ) < 0)
{
return -1;
}
else
{
nStatus |= TIOCM_RTS;
if ( ioctl( _port, TIOCMSET, &nStatus ) < 0)
{
return -2;
}
}
return 0;
}
int set_to_read( int _port )
{
int nStatus;
if ( ioctl( _port, TIOCMGET, &nStatus ) < 0)
{
return -1;
}
else
{
nStatus &= ~TIOCM_RTS;
if ( ioctl( _port, TIOCMSET, &nStatus ) < 0)
{
return -2;
}
}
return 0;
}
To send bytes I have this code
set_to_write(port);
write(port,"bytes to send",len);
tcdrain(port)
set_to_read(port);
All is running succesfully but when I put oscilloscope I can see 10 mS (or
more) latency time from set_to_write() to write() begin to send
characters. I know this is a Linux userland issue but, is there another
way to do this from driver, similar a cflag CRTSCTS to activate RTS/CTS
protocol?.
If there is not another way, which shall be the best strategy to implement
this (activate RTS when uart is transmiting data and deactivate when
transmision is finish. It would be another protocol different but similar
to RTS/CTS protocol) on linux driver (modifying serial_core.c to accept a
new CFLAG?) ?
thank you very munch for your help.
José Luis Zabalza
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