Linux a komunikace pres 485

[Stanislav Meduna]

On 11 Apr 1999 13:26:48 +0200, Ivo Zacek wrote:

: Pokud jde o ty prevodniky, tak jsem pro ne psal driver pro DOS. Protoze
: RS485 je poloduplex, musi se prepinat prijem/vysilani. Obvykle se to
: dela signalem RTS. Tady je problem, ze bezne seriove porty typu 16*50
: nedavaji preruseni, kdyz vysilani skutecne fyzicky skonci.

Pokial nie je absolutnou prioritou okamzita reakcia,
nie je problem poll-ovat stav registrov - ci uz z jadra,
alebo z user space. Komentar v drivers/char/serial.c
napr. pise:

  /*
   * get_lsr_info - get line status register info
   *
   * Purpose: Let user call ioctl() to get info when the UART physically
   * 	    is emptied.  On bus types like RS485, the transmitter must
   * 	    release the bus after transmitting. This must be done when
   * 	    the transmit shift register is empty, not be done when the
   * 	    transmit holding register is empty.  This functionality
   * 	    allows an RS485 driver to be written in user space. 
   */
static int get_lsr_info(struct async_struct * info, unsigned int *value)
{


Vysledok tejto funkcie je do userspace mozne
dopravit cez ioctl TIOCSERGETLSR.

Existuje tiez funkcia rs_wait_until_sent(), ktora pocka
(samozrejme prerusitelne), kym sa vsetko posle von
a zda sa, ze sa snazia aj o minimalne oneskorenie:

        /*
         * Set the check interval to be 1/5 of the estimated time to
         * send a single character, and make it at least 1.  The check
         * interval should also be less than the timeout.
         * 
         * Note: we have to use pretty tight timings here to satisfy
         * the NIST-PCTS.
         */


Ako tak grepujem jadro a manualy dalej, objavil som aj funkciu
tcdrain, ktora by mala robit to iste na lubovolnom deskriptore.

Zdravi
-- 
				Stano