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ssss -- Device Driver


The device driver ssss lets you use SCSI interface devices attached to any of
the following host adapters:

    Future Domain TMC-845/850/860/875/885
    Future Domain TMC-840/841/880/881
    Seagate ST01/ST02

This driver  has major number  13.  It can  be accessed either  as a block-
special  device  or  as  a  character-special  device.   The  minor  number
specifies the device and  partition number for disk-type devices; this lets
you use up to eight SCSI-IDs,  with one logical unit number (LUN) per SCSI-
ID and  up to four partitions  per LUN.  The present  version supports only
LUN 0 per SCSI-ID.

The first  ooppeenn call on a  SCSI disk device reads  the partition table into
memory.

_C_o_n_t_r_o_l_l_e_r _C_o_n_f_i_g_u_r_a_t_i_o_n
For your Future  Domain or Seagate host adapter to  work with COHERENT, you
must install  it with  interrupts enabled.  If  you have been  running your
host adapter  with interrupts disabled,  a good first  choice for interrupt
number is IRQ 5, unless you  know that you have another device installed on
your computer  that already uses this  interrupt.  Consult the instructions
provided with your host adapter,  and the jumper settings, to determine the
IRQ number.

The base  address value  used by ssss  is the four-digit  hexadecimal memory-
segment number of the host adapter's starting address.  This number is most
often CCAA0000; other  common values are CC880000, CCCC0000, CCEE0000,  DDCC0000, and DDEE0000. You
must use  the correct value,  as specified by  the jumper settings  on your
host adapter.

Device driver  variables SSSS_BBAASSEE and SSSS_IINNTT correspond  to the base address
and interrupt vector, respectively.  Device driver variable NNSSDDRRIIVVEE must be
patched before  the driver is loaded.  The low-order  byte of this variable
is a bit  map that indicates the SCSI-IDs of  all installed target devices.
The high-order byte indicates the type of host adapter.  Labelling the bits
in the low-order byte of NNSSDDRRIIVVEE is as follows:

       _B_i_t _n_u_m_b_e_r:  7 6 5 4 3 2 1 0 <- _l_e_a_s_t _s_i_g_n_i_f_i_c_a_n_t _b_i_t

There should  be a value of  one for each installed  target device.  Do not
set a  value of one  for the SCSI-ID  of the host  adapter.  The high-order
byte  of  NNSSDDRRIIVVEE  is  00xx0000  for  Seagate ST01  and  ST02,  00xx8800  for  TMC-
845/850/860/875/885, and 00xx4400 for TMC-840/841/880/881.  For example, if you
are using a TMC-885 and a  single hard drive with SCSI ID of zero, then set
NNSSDDRRIIVVEE  to 0x8001.   See  Lexicon article  hhss  for an  example  of how  to
configure a device driver.

When  processing BIOS  I/O requests  prior to  booting COHERENT,  SCSI host
adapters  use  ``translation-mode''  drive  parameters:  number  of  heads,
cylinders, and  sectors per track.   These numbers are  called translation-
mode  parameters  because  they have  nothing  to  do  with physical  drive
geometry.  The translation-mode parameters used by the BIOS code present on
your host adapter  can be obtained using the ddppbb  utility found on the boot
diskette of versions 3.2.0 and later of COHERENT.

ssss has  a table, ddrrvv_ppaarrmm,  which contains eight two-word  entries, one for
each  possible SCSI-ID.   The first  word  of each  entry must  contain the
number of cylinders for the drive.   The high-order byte of the second word
is the  number of sectors  per track; the  low-order byte is  the number of
heads.   Entries in  ddrrvv_ppaarrmm should  be  patched for  each drive  which is
accessible by the BIOS.  Values need not be patched for drives inaccessible
by the BIOS.   Note that BIOS code is executed  by COHERENT only during the
initial  bootstrap.  After  that, drive  parameters  are of  no consequence
because SCSI I/O requests are  based upon logical block number, rather than
upon cylinder/head/sector addressing.

The installation  procedure for COHERENT  versions 3.2.0 and  later patches
all necessary  variables for the  accompanying version of the  ssss driver by
executing the command:

    /etc/mkdev scsi

_M_i_n_o_r _D_e_v_i_c_e _N_u_m_b_e_r_s
ssss usually  uses the special files /ddeevv/ssdd*  and /ddeevv/rrssdd*. For information
on the meaning  of minor numbers with these special  files, see the article
on aahhaa115544xx.

_L_o_a_d_i_n_g _t_h_e _D_r_i_v_e_r (_C_O_H_E_R_E_N_T _2_8_6 _o_n_l_y)
ssss must be  loaded on a COHERENT 286 system  that does not have a SCSI hard
disk as the root device.  To do so, use the command /eettcc/ddrrvvlldd, as follows:

    /etc/drvld -r /drv/ss

_F_i_l_e_s
/ddeevv/ssdd* -- block-special devices
/ddeevv/rrssdd* -- character-special devices

_S_e_e _A_l_s_o
ddeevviiccee ddrriivveerrss, ddrrvvlldd, ssccssii

_N_o_t_e_s
Current releases  of ssss support  disk-type devices only.  Zero  is the only
LUN  allowed.  Future  versions will  add support  for tape-type  and other
devices, as well as nonzero LUN's.

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