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Annotation of coherent/a/usr/man/COHERENT/com, revision 1.1

1.1     ! root        1: 
        !             2: 
        !             3: com                       Device Driver                       com
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        !             8: Device drivers for asynchronous serial lines
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        !            10: 
        !            11: The  COHERENT system  has  drivers for  four asynchronous  serial
        !            12: lines, ccoomm11 through ccoomm44.
        !            13: 
        !            14: A  serial  line  can   be  opened  into  any  of  four  different
        !            15: ``flavors'', as follows:
        !            16: 
        !            17: 
        !            18:      ccoomm?ll     Interrupt driven, local mode (no modem control)
        !            19:      ccoomm?rr     Interrupt driven, remote mode (modem control)
        !            20:      ccoomm?ppll    Polled, local mode (no modem control)
        !            21:      ccoomm?pprr    Polled, remote mode (modem control)
        !            22: 
        !            23: 
        !            24: ``Local mode''  means that the line will  have a terminal plugged
        !            25: into  it, to  directly  access the  computer.  ``Modem  control''
        !            26: means that  the line  will have a  modem plugged into  it.  Modem
        !            27: control  is  enabled on  a  serial line  by  resetting the  modem
        !            28: control bit  (bit 7)  in the minor  number for the  device.  This
        !            29: allows  the system  to generate  a hangup  signal when  the modem
        !            30: indicates loss of  carrier by dropping DCD (Data Carrier Detect).
        !            31: A  modem  line should  always  have  its DSR,  DCD  and CTS  pins
        !            32: connected.   If  left  hanging,  spurious transitions  can  cause
        !            33: severe  system thrashing.   To disable modem  control on  a given
        !            34: serial line, use the minor device which has the modem control bit
        !            35: set (bit 7).  An ooppeenn to  a modem-control line will block until a
        !            36: carrier is detected (DCD goes true).
        !            37: 
        !            38: ``Interrupt mode'' means  that the port can generate an interrupt
        !            39: to attract the  attention of the COHERENT system; ``polled mode''
        !            40: means that  the port  cannot generate  an interrupt, but  must be
        !            41: checked (or ``polled'')  constantly by the COHERENT system to see
        !            42: if activity has occurred on it.
        !            43: 
        !            44: The  COHERENT system  uses two  device  drivers to  manage serial
        !            45: lines: one  driver manages COM1  and COM3, and  the other manages
        !            46: COM2 and  COM4.  Due to  limitations in the design  of the ports,
        !            47: you can enable  interrupts on either COM1 or COM3  (or on COM2 or
        !            48: COM4),  but   not  both.    If  you   wish  to  use   both  ports
        !            49: simultaneously, one must be  run in polled mode.  For example, if
        !            50: you wish to  open all four serial lines, you  can open two of the
        !            51: lines  in interrupt  mode: you  can open either  COM1 or  COM3 in
        !            52: interrupt mode, and you can open either COM2 or COM4 in interrupt
        !            53: mode.  The other two lines must be opened in polled mode.
        !            54: 
        !            55: Opening a  device in polled mode consumes  many CPU cycles, based
        !            56: upon the speed of  the highest baud rate requested.  For example,
        !            57: on a  20 MHz 80386-based machine, polling  at 9600-baud was found
        !            58: to consume about 15% of the CPU time.  As only one device can use
        !            59: the interrupt  line at  any given time,  the best approach  is to
        !            60: make the  high-speed line of  the pair interrupt  driven and open
        !            61: the  low-speed  or  less-frequently  used  line in  polled  mode.
        !            62: 
        !            63: 
        !            64: COHERENT Lexicon                                           Page 1
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        !            69: com                       Device Driver                       com
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        !            72: 
        !            73: However, if you enable a polled line for logins, the port is open
        !            74: and will  be polled as  long as the port  remains open (enabled).
        !            75: Thus, even if a port is  not in use, the fact that it has a ggeettttyy
        !            76: on it  consumes CPU cycles.  As  a rule of thumb,  try and open a
        !            77: port in  interrupt mode.  If you cannot,  use the polled version.
        !            78: Also note that use of any of the four serial ports in polled mode
        !            79: prevents  other polled  serial  device drivers,  such  as the  hhss
        !            80: generic multi-port  polled serial driver, from  being used at the
        !            81: same time.
        !            82: 
        !            83: If you intend to use a modem on your serial port, you must insure
        !            84: that the DCD signal from  the modem actually _f_o_l_l_o_w_s the state of
        !            85: carrier detect.   Some modems allow the user  to ``strap'' or set
        !            86: the  DCD  signal so  that  it is  always  asserted (true).   This
        !            87: incorrect setup  will cause COHERENT  to think that  the modem is
        !            88: ``connected''  to a  remote  modem, even  when there  is no  such
        !            89: connection.
        !            90: 
        !            91: In addition, if you wish  to allow remote logins to your COHERENT
        !            92: system via  your modem, you  must insure that the  modem does nnoott
        !            93: echo any  commands or status information.  Failure  to do so will
        !            94: result  in severe  system  thrashing due  to the  ggeettttyy or  llooggiinn
        !            95: processes endlessly ``talking'' to your modem.
        !            96: 
        !            97: ***** Changing Default Port Speeds *****
        !            98: 
        !            99: Serial lines ccoomm11 through  ccoomm44 default to 9600 baud when opened.
        !           100: This default  speed can  be permanently  changed on a  "per port"
        !           101: basis by changing the value of driver variables CC11BBAAUUDD_, CC22BBAAUUDD_,
        !           102: CC33BBAAUUDD_ or CC44BBAAUUDD_. The list of acceptible values can be found in
        !           103: header file <ssggttttyy.hh> and range from 1, corresponding to 50 baud,
        !           104: up to 17, which corresponds to 19,200 baud.  For a table of legal
        !           105: baud rates, see the Lexicon entry for ssggttttyy.hh.
        !           106: 
        !           107: To  change  the  default value  for  a  port,  you  must use  the
        !           108: /ccoonnff/ppaattcchh command.   For example,  to change the  default speed
        !           109: for port  ccoomm22 to  2400 baud,  enter the following  command while
        !           110: running as the superuser:
        !           111: 
        !           112: 
        !           113:           /conf/patch /drv/al1 C2BAUD_=12
        !           114: 
        !           115: 
        !           116: The change will not take effect until the next time that you boot
        !           117: your system.
        !           118: 
        !           119: ***** See Also *****
        !           120: 
        !           121: ccoomm11, ccoomm22, ccoomm33, ccoomm44, ddeevviiccee ddrriivveerrss
        !           122: 
        !           123: ***** Diagnostics *****
        !           124: 
        !           125: An  attempt to  open a  non-existent  device will  generate error
        !           126: messages.  This can occur if hardware is absent or not turned on.
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        !           128: 
        !           129: 
        !           130: COHERENT Lexicon                                           Page 2
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        !           135: com                       Device Driver                       com
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        !           137: 
        !           138: 
        !           139: ***** Notes *****
        !           140: 
        !           141: The ccoomm*  series of devices  are not compatible  with the iiooccttll()
        !           142: parameters defined in  header file <tteerrmmiioo.hh>. Be sure to include
        !           143: header file  <ssggttttyy.hh> if you  wish to perform  terminal specific
        !           144: iiooccttll() calls.
        !           145: 
        !           146: In the  current version of these  drivers, the following sequence
        !           147: of steps results in a panic:
        !           148: 
        !           149: 
        !           150:           enable com4pl
        !           151:           enable com3pl
        !           152:           disable com4pl
        !           153:           kill kill <al1 driver process id>
        !           154: 
        !           155: 
        !           156: The key is that  the driver containing the polling routine cannot
        !           157: be unloaded if the other driver is still polling.
        !           158: 
        !           159: Note, too, that if any ccoomm device driver is used in polling mode,
        !           160: the hhss driver cannot be used, and vice versa.
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        !           196: COHERENT Lexicon                                           Page 3
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