PROJECT:        MAC REPLACEMENT PROJECT

DOC. TYPE:      TECHNICAL NOTE
TITLE:          Illegal Instruction Executive  Functions  and  Calling
                    Sequences
SUBJECT:        

GROUP:          SYSTEM EXTENSIONS
AUTHOR:         D.B.Curtis

DOC NO.:        70
DATE:           25-JUN-79 15:46
FILE:           ILLCODE.RNO


                    MODIFIED:  19 JUL 79 16:58


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1.0  INTRODUCTION

This document is a result of document  #34.   This  and  document  #67
describe the use of hte illegal instruction executive functions.



1.1  Objectives

This document describes the functions and calling  sequences  for  the
illegal   instruction  extensions  to  the  RSX-11M  executive.   This
document  does  not  attempt  to  justify  the  extensions   as   this
justification  exists  in  the  design  specification ( document #34).
This  document  describes  the  executive   extensions   and   calling
sequences.



1.2  Discussion

The executive has the following additional functions:

     1.  Large Array Handling

         A set of functions that allow access to regions without being
         mapped to that region.




2.0  LARGE ARRAY HANDLING

The task must first attach  to  a  region.   The  region  ID  will  be
returned  to  the  task.   This  region ID must be used in the calling
sequence.  If this ID is incorrect, the illegal instruction will cause
an illegal instruction trap.



2.1  Usage (calling sequences)

The  instruction  that  starts  the  system  function  has  the  octal
representation  210.   The  arguments  of  the  instruction are on the
stack.  There are the following types.

     1.  TYPE 0 -- transfer word to user

     2.  TYPE 1 -- transfer word from user


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     3.  TYPE 2 -- transfer block of words to user

     4.  TYPE 3 -- transfer block of words from user

     5.  TYPE 4 -- set a block of area to user specified value

Each of these types have the following information on the stack at the
time  of  the 210 instruction execution.  This information is required
for each type.  Each type may have other  information  placed  on  the
stack along with the required information.
        
        10(SP) INDEX HIGH PART
         6(SP) INDEX LOW PART
         4(SP) REGION ID WORD OBTAINED FROM ATTACH REGION
         2(SP) TYPE
          (SP) RAD50 REPRESENTATION OF "ILL"

Where the INDEX is a 24-bit byte index into the region.

For type 0:

no more needed information

For type 1:

12(SP) VALUE TO BE STORED IN THE REGION

For type 2:

14(SP) NUMBER OF BYTES TO TRANSFER
12(SP) VIRTUAL ADDRESS TO TRANSFER TO 

For type 3:

14(SP) NUMBER OF BYTES TO TRANSFER
12(SP) VIRTUAL ADDRESS TO TRANSFER FROM 

For type 4:

14(SP) NUMBER OF BYTES TO SET
12(SP) VALUE TO SET INTO AREA

All cases except type 0 finish the operation with the  stack  cleared.
Type  0  returns the value obtained from the area on the stack.  Carry
clear implies operation completed successfully.  Carry set implies  an
error,  the  stack  is  not  cleared.  The instruction will produce an
illegal instruction AST for the following:

     1.  The  instruction  used  to  cause  the  trap  is  an  illegal


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         instruction other than "210".

     2.  The  first  word  of  the  user's  stack  is  not  the  RAD50
         representation of "ILL".

     3.  The TYPE argument is out of range.

     4.  The region specified does not exist or is not attached to the
         task.

     5.  The high part of the index is non-zero.

The instruction will return carry set for the following:

     1.  If the index is odd.

     2.  If the index points outside the region.

     3.  If the block transfer/set would attempt  access  outside  the
         region.

     4.  If the block transfer/set has a zero byte count.




3.0  GLOSSARY