

                   Help information for EI.SYS                              06 Sep 82

















                              Summary


                 Program name:          EI.SYS

                 Programmers name:      P.C.Waggett

                 PURPOSE:               Emulate EIS instruction set on BIS machines.

                 Language:              MACRO Assembler.

                 Operating system:      RT-11

                 Machine dependence:    PDP-11

                 Special devices:       None

                 Core store:            Driver occupies 2466 Octal bytes.

























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                   Help information for EI.SYS                              06 Sep 82


                 CONTENTS


      i . . . . . Summary
    iii . . . . . 1.0 Introduction
    iii . . . . . 2.0 Using the Emulator
    iii . . . . . 3.0 Set options available
    iii . . . . . 4.0 Operating restrictions
     iv . . . . . 5.0 Debug aids
     iv . . . . . 6.0 Programme test
     iv . . . . . 7.0 Programme Modification















































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                   Help information for EI.SYS                              06 Sep 82


     1.0 Introduction

This programme was written to emulate the EIS instructions MUL, DIV, SOB, ASH,  ASHC,
SXT and XOR on a BIS machine.  The driver is available on request from T63B.

     2.0 Using the Emulator

EI.SYS must be Installed, Loaded and then Set ON.
i.e.
                 INS EI ( Should not be required, but may be )
                 LOA EI
                 SET EI ON
The  last  operation  alters  the  driver  name to <Space Z> and the driver cannot be
removed until a SET EI OFF is performed.  This means that it cannot be unloaded  from
a  programme,  or used after loading from a programme.  These operations MUST be done
from the console.  Once this process is complete EIS instructions will  be  emulated,
transparently  to  the user, by software.  Any none emulated instruction will TRAP as
usual.

     3.0 Set options available

Four options are available:-
          ON.....This enables the driver.  It puts the entry address of the driver in
the M-TRAP location.(10).
          OFF.....This disables the driver.  It puts the address of the RT-11 Monitor
TRAP handling routine in location 10.
          BIS.....Clear BIT 400 at 370(RMON).Clears the EIS available bit.
          EIS.....Sets  BIT 400 at 370(RMON).Sets  the EIS available bit.

If try to set EI ON when driver is already set ON, or any other illegal  option,  the
message  EI-BAD  appears.   If try to unload EI when EI is SET ON, the message EI-DEV
appears.

The driver alters its own name in P$TABLE ( P$TABLE is a monitor RT-11  table)  hence
if  do  a  SH<CR>  EI will not be present but Z will be.  If do a SH D<CR> then EI is
present but Z is not.  This occurs because SH D lists all SYS  files  on  the  system
disc.  The SH lists all the devices in P$TABLE.


     4.0 Operating restrictions

The  driver  emulates  all  sensible  (  and probably all non-sensible) EIS assembler
instructions using any combination of registers, including PC and SP.  All addressing
modes  are  emulated.  No known faults exist.  To aid fault finding the driver should
be reassembled with DEBUG=1.  This enables the programmer to examine each  instuction
which  causes  the emulator to be entered and gives some information on the errors in
processing.  (see 5.0 ).











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                   Help information for EI.SYS                              06 Sep 82


     5.0 Debug aids

(1) A routine (LOOK) is called on entering the driver.  This routine looks at bit  15
of  the  Console  switch-register.   If  this switch is up (SET), the programme loops
until the switch is put down, whence programme execution continues.  While in waiting
loop,  register  R2  (1777702)  contains  the  instruction  the  emulator is about to
process.  After execution the location SAVINS contains the last instruction  emulated
by  the driver.  Hence if the driver dies, this location can be examined to see which
instruction caused the crash !

(2) Divide by zero or overflow in DIV is detected and a message EI-ABORT is  sent  to
the console.

     6.0 Programme test

The  driver allows programs DCREM, FLTSPC (Compiled with CODE=EIS), RUNOFF etc to run
on ALTAIR (11/10).  T63B would be interested in other programmes that run/do not  run
! on the emulator.  Programme size is 2466 Octal Bytes.





     7.0 Programme Modification

This  programme  is  NOT  easy  to  follow  as  it  is  full of self-modifying code !
Hopefully, the comments will enable other programmers  to  follow  the  ideosyncratic
programming.   The  option  part  of the code is especially bad as space was in short
supply and every trick to save space was employed !.  Similarly in the MAIN emulator.
PLEASE  do NOT modify the source without first consulting T63B, who will otherwise be
VERY annoyed.  Any errors found in the program will be remorselessly tracked down and
painfully eliminated.


























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