how to talk to the serial and parallel ports through a C

[Dan Nelson]

In the last episode (Jun 11), Bernard Dugas said:
> Not sure, but i'm using the serial port only to read and write
> electrical values, to command power relays. On mickey systems, serial
> drivers are far to complicated for that.
> 
> Did anybody write a simple kernel module doing just that ?
> 
> #include <sys/io.h>
> #include <stdio.h>
> 
> void getComValues(int adr,unsigned char *p_TxdS3,
> unsigned char *p_DtrS4,unsigned char *p_RtsS7,
> unsigned char *p_CtsE8,unsigned char *p_DsrE6,
> unsigned char *p_RiE9,unsigned char *p_DcdE1)
> {
>   unsigned char val3,val4,val6;
> 
>   val3=inb(adr+3);
>   *p_TxdS3=(val3&64)>>6 ; //récupère le bit 6
> 
>   val4=inb(adr+4);
>   *p_DtrS4=val4&1 ;       //récupère le bit 0
>   *p_RtsS7=(val4&2)>>1 ;  //récupère le bit 1
> 
>   val6=inb(adr+6);
>   *p_CtsE8=(val6&16)>>4 ;  //récupère le bit 4
>   *p_DsrE6=(val6&32)>>5 ;  //récupère le bit 5
>   *p_RiE9=(val6&64)>>6 ;   //récupère le bit 6
>   *p_DcdE1=(val6&128)>>7 ; //récupère le bit 7

Take a look at the tty(4) manpage; you should be able to open
/dev/cuaa0 (aka COM1), then use the TIOCMGET and TIOCMSET ioctls to get
and set the appropriate status bits, all from userland.  The
comms/sredird port uses this to provide remote virtual serial ports
with perfect control.

-- 
	Dan Nelson
	dnelson at allantgroup.com