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llpp -- Device Driver


Files  /ddeevv/llpp*  access  the  line-printer's  device  drivers  for  IBM  AT
COHERENT.  The drivers are assigned major device number 3.

The COHERENT system supports three  printers, in both cooked and raw modes.
The following gives the device name, minor device, and I/O port:

/ddeevv/llpptt11 0  0x3BC  (/etc/mknod /dev/lpt1  c 3   0)
/ddeevv/llpptt22 1  0x378  (/etc/mknod /dev/lpt2  c 3   1)
/ddeevv/llpptt33 2  0x278  (/etc/mknod /dev/lpt3  c 3   2)
/ddeevv/rrllpptt11128  0x3BC  (/etc/mknod /dev/rlpt1 c 3 128)
/ddeevv/rrllpptt22129  0x378  (/etc/mknod /dev/rlpt2 c 3 129)
/ddeevv/rrllpptt33130  0x278  (/etc/mknod /dev/rlpt3 c 3 130)

``Cooked'' processing  processes the special characters  BS (backspace), HT
(horizontal tab), LF (line feed),  FF (form feed), and CR (carriage return)
appropriately; raw processing simply passes them on to the printer.

_K_e_r_n_e_l _V_a_r_i_a_b_l_e_s
Please  note  that the  COHERENT  286 kernel  references  variables with  a
trailing  underscore character;  for  example, aattppaarrmm_.   The COHERENT  386
kernel, however, does _n_o_t use a trailing underscore; for example, aattppaarrmm.

The following descriptions apply to both COHERENT 286 and COHERENT 386, but
the notation will be in the COHERENT-386 form.

_D_i_s_c_i_p_l_i_n_e
The driver  uses a hybrid busy-wait/timeout  discipline to support printers
efficiently that have varying buffer sizes in a multi-tasking environment.

The kernel variable LLPPWWAAIITT sets the  time for which the processor waits for
the printer  to accept  the next  character.  If the  printer is  not ready
within the LLPPWWAAIITT period,  the processor then resumes normal processing for
the number  of ticks set  by by the  kernel variable LLPPTTIIMMEE.  Thus, setting
LLPPWWAAIITT to  an extremely  number (e.g.,  1,000) and LLPPTTIIMMEE  to a  very small
number  (e.g., one)  results in  a fast  printer, but  leaves very  few CPU
cycles available for anything  else.  Conversely, setting LLPPWWAAIITT to a small
number  (e.g., 50)  and LLPPTTIIMMEE  to a  large number  (e.g., five)  result in
efficient  multi-tasking but  also  results in  a slow  printer unless  the
printer  itself contains  a buffer  (as is  normal with  all but  the least
expensive printers).  By default, LLPPWWAAIITT is set to 400 and LLPPTTIIMMEE to four.

We recommend that you set LLPPWWAAIITT to no less than 50 and no more than 1,000,
and LLPPTTIIMMEE to no less than  one.  To change the values of LLPPWWAAIITT to 500 and
LLPPTTIIMMEE to one, use the following command:

    /conf/patch -k /coherent LPWAIT=500 LPTIME=1

The kernel  variable LLPPTTEESSTT determines whether the  device driver checks to
see  if the  printer is  in  an ``on-line''  condition before  it uses  the
device.  If your printer does not  support this signal, you must set LLPPTTEESSTT
to zero.

_F_i_l_e_s
/ddeevv/llpp* -- ``Cooked'' printer interfaces
/ddeevv/rrllpp* -- Raw printer interfaces

_S_e_e _A_l_s_o
aasscciiii, ddbb, ddeevviiccee ddrriivveerrss, eeppssoonn, llpprr

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