Rtems_termios_ioctl problem

[Thomas Doerfler]

Stephane,

the input direction looks fine for me with one exception: the function
InputFlowCheckResume should be executed with interrupts disabled,
otherwise "rawOutBufState" could change its state after it has been
checked and before the (*write) function is executed.

But I am quite unsure about the output direction: in interrupt driven
mode, termios will present the buffer between head and tail (or part of
it) to the driver's write function, and some time later, the driver will
 call rtems_termios_dequeue_characters(tty,len) to indicate, that it has
sent out the whole or part of this buffer.

What happens, when you meanwhile modify "head" (and possibly add new
output characters to the buffer afterwards)? Either the driver will send
out stale data, new data out of proper order, or the head/tail
management may totally come out of sync in this situation.

I am not sure what will happen, but I think your output Flush needs
further rethinking.

wkr,
Thomas.


Arquer Stephane schrieb:
> Hi,
> 
> If my understanding is correct, in the case of using the flow ctrl mode  XON/XOFF or RTS we need to send these controls to indicate that the input buffer has enough space for further reception.
> So , I've added the corresponding code when flushing input buffer like following.
> 
> 
> 
> /*
>  *	helper subroutine which checks if XON must be sent
>  *  it takes also care of the HW flow control
>  */
> static rtems_status_code InputFlowCheckResume (struct rtems_termios_tty *tty)
> {	
> /* if tx stopped and XON should be sent... */
> 	if (((tty->flow_ctrl & (FL_MDXON | FL_ISNTXOF))
>     	==                (FL_MDXON | FL_ISNTXOF))
> 		&& ((tty->rawOutBufState == rob_idle)
> 		|| (tty->flow_ctrl & FL_OSTOP))) {
>     	/* XON should be sent now... */
>     	(*tty->device.write)(tty->minor, &(tty->termios.c_cc[VSTART]), 1);
> 	}
> 	else if (tty->flow_ctrl & FL_MDRTS) {		    
>     	tty->flow_ctrl &= ~FL_IRTSOFF;		
>     	/* activate RTS line */
> 	    if (tty->device.startRemoteTx != NULL) {
> 	      tty->device.startRemoteTx(tty->minor);
> 	    }
>  	} 	
>  	return RTEMS_SUCCESSFUL; 	
> } // InputFlowCheckResume()
> 
> 
> rtems_status_code rtems_termios_ioctl (void *arg){
> ...
> case TCFLSH:
> 		{
> 		switch (args->buffer) {
> 			case TCIFLUSH:	/* flush input buffer */
> 				{												
> 				if ( tty->rawInBuf.Tail != tty->rawInBuf.Head ) {/* buffer is not empty*/
> 					rtems_interrupt_disable (level);
> 					tty->rawInBuf.Head = tty->rawInBuf.Tail;
> 					rtems_interrupt_enable (level);
> 					sc = InputFlowCheckResume(tty);
> 					}
> 				}
> 				break;				
> 			case TCOFLUSH:	/* flush output buffer*/
> 				{
> 				if ( tty->rawOutBuf.Tail != tty->rawOutBuf.Head ) {/* buffer is not empty*/
> 					rtems_interrupt_disable (level);
> 					tty->rawOutBuf.Head = tty->rawOutBuf.Tail;
> 					rtems_interrupt_enable (level);
> 					}			
> 				}
> 				break;				
> 			case TCIOFLUSH:	/* flush input & output buffer*/
> 				{
> 				if ( tty->rawInBuf.Tail != tty->rawInBuf.Head ){
> 					rtems_interrupt_disable (level);
> 					tty->rawInBuf.Head = tty->rawInBuf.Tail;
> 					rtems_interrupt_enable (level);
> 					sc = InputFlowCheckResume(tty);	
> 					}							
> 				if ( tty->rawOutBuf.Tail != tty->rawOutBuf.Head ) {
> 					rtems_interrupt_disable (level);
> 					tty->rawOutBuf.Head = tty->rawOutBuf.Tail;
> 					rtems_interrupt_enable (level);
> 					}
> 				}
> 				break;
> ...
> 
> 
> Kind regards.
> 
> Stéphane.
> 
>> -----Message d'origine-----
>> De : Thomas Doerfler [mailto:Thomas.Doerfler at imd-systems.de] 
>> Envoyé : mercredi 2 mai 2007 22:30
>> À : Joel Sherrill
>> Cc : Eric Norum; rtems-users at rtems.org; Arquer Stephane
>> Objet : Re: RE : Rtems_termios_ioctl problem
>>
>>
>> Joel,
>>
>> Joel Sherrill schrieb:
>>> Thomas Doerfler wrote:
>>>
>>>   
>> Should this code be moved to a helper subroutine that is 
>> invoked from both places?
>>
>> Yes Joel, this would be nice, especially since it only 
>> requires "tty" as an argument. The name of this function 
>> could be "inputFlowCheckResume" or something like this...
>>
>> Stephane, can you try to implement this?
>>
>> wkr,
>> Thomas.
>>
>> -- 
>> --------------------------------------------
>> IMD Ingenieurbuero fuer Microcomputertechnik
>> Thomas Doerfler           Herbststrasse 8
>> D-82178 Puchheim          Germany
>> email:    Thomas.Doerfler at imd-systems.de
>> PGP public key available at:
>>      http://www.imd-systems.de/pgpkey_en.html
>>
> 
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