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	TITLE	LODMAP
	SEARCH MONSYM
	ENTRY MAPIT,DEMAP
;
;
;
;	COPYRIGHT (C) DIGITAL EQUIPMENT CORPORATION 1982, 1986.
;	ALL RIGHTS RESERVED.
;
;	THIS SOFTWARE IS FURNISHED UNDER A LICENSE AND MAY  BE  USED  AND
;	COPIED ONLY IN ACCORDANCE WITH THE TERMS OF SUCH LICENSE AND WITH
;	THE INCLUSION OF THE ABOVE COPYRIGHT NOTICE.   THIS  SOFTWARE  OR
;	ANY  OTHER  COPIES  THEREOF MAY NOT BE PROVIDED OR OTHERWISE MADE
;	AVAILABLE TO ANY OTHER PERSON.  NO TITLE TO AND OWNERSHIP OF  THE
;	SOFTWARE IS HEREBY TRANSFERRED.
;
;	THE INFORMATION IN THIS SOFTWARE IS  SUBJECT  TO  CHANGE  WITHOUT
;	NOTICE  AND  SHOULD  NOT  BE CONSTRUED AS A COMMITMENT BY DIGITAL
;	EQUIPMENT CORPORATION.
;
;	DIGITAL ASSUMES NO RESPONSIBILITY FOR THE USE OR  RELIABILITY  OF
;	ITS SOFTWARE ON EQUIPMENT THAT IS NOT SUPPLIED BY DIGITAL.
;
;
;
;
; REVISION HISTORY:
;
;
; END OF REVISION HISTORY
;
;
;
;				FUNCTION
; This sub-module is used to copy all the pages from section 0
; to section 1.  If DDT is present, MAPIT  will make it run in a non-zero
; section.  MAPIT is called from section 0; it runs in section 0 until
; all the mapping has been done. Finally, it jumps to section 1 and arranges
; to return in section 1.
;
; Please note that this module was taken from the chapter on
; "DECSYSTEM-20 ASSEMBLY LANGUAGE PROGRAMMING".
;
; DEMAP (which is not from the book mentioned above) returns the code
; to section 0, and then resets the stack pointer and the return PC 
; on the stack, so that calls within section 0 may proceed normally.
;
;			General Usage Notes:
;
; The MAPIT routine should be called shortly after starting a program.
;
; The DEMAP routine is for use primarily in BLISS programs.
; DEMAP should be called from the same routine which
; called MAPIT, just before that routine returns.  Thus, if
; MAPIT is called in the first line of a MAIN routine, DEMAP
; should be the last routine call, just before the routine returns
; or ends.

	AC1=1
	AC2=2
	AC3=3
	AC4=4
	AC5=5
	SP=17

	TWOSEG
	RELOC	0
SPLH:	0			;Left half of Stack Pointer
STKLH:	0			;Left half of Stack
	RELOC	400000

MAPIT:
	HLLZ	AC1,SP		;Fetch left half of stack ptr
	HLLM	AC1,SPLH	;Store it away
	HLLZ	AC1,(SP)	;Left half of return address
	HLLM	AC1,STKLH	;Store away return LH
	MOVEI	AC1,0		;Make a private section
	MOVE	AC2,[.FHSLF,,1]	;Section 1
	MOVE 	AC3,[PM%CNT!PM%RD!PM%WR!PM%EX!1] ;One section with all access
	SMAP%
	ERJMP	.+1		;Shouldn't fail if SMAP% exists
	MOVE	AC4,[.FHSLF,,0]	;Initial fork page pointer
MAP1:	MOVE 	AC1,AC4		;Fork,,page #
	RMAP			;Read fork's map
	CAMN	AC1,[-1]	;-1 means no access
	JRST	MAP2		;No work for no page
	MOVE 	AC3,AC2		;Access bits from RMAP
	MOVE	AC2,AC4		;Fork,,source page #
	IORI	AC2,1000	;Fork,,destination page #
	PMAP			;Copy map from sect 0 to 1
	ERJMP	.+1		;Unexpected failure
MAP2:	ADDI	AC4,1		;Increment fork page pointer
	TRNN	AC4,1000	;Done yet?
	JRST	MAP1

;Now unmap UDDT from section 0
;+
;  IGNORE DDT FOR NOW - WITH THE NEW DDT, WE MAY NOT NEED THIS
;-
	JRST	MAP5		;FORGET DDT TWIDDLING
	SETO	AC1,		;Unmap process page
	MOVE	AC2,[.FHSLF,,771] ;Unmap UDDT from section 0
	MOVE	AC3,[PM%CNT!7]	;Remove pages 771 through 777
	PMAP
	ERJMP	.+1		;Ignore errors
	MOVE	AC1,[.FHSLF,,770] ;Is UDDT present?
	RMAP
	CAMN	AC1,[-1]
	JRST	MAP5		;No DDT at all.

;Make section 0 UDDT jump to section 1.
;We can't write this page 770, so we discard it.

	PUSH	SP,770000	;Save 770000,1,2
	PUSH	SP,770001
	PUSH	SP,770002
	SETO	AC1,
	MOVE 	AC2,[.FHSLF,,770] ;Unmap page 770
	MOVEI	AC3,0
	PMAP
	ERJMP .+1
	POP	SP,770002	;Put back 3 words.
	POP	SP,770001
	POP	SP,770000
	MOVE	AC1,[XJRSTF 770004] ;The starting instruction
	MOVEM	AC1,770003	;for UDDT goes into 770003
	SETZM	770004		;new PC flags for XJRSTF
	MOVE	AC1,[1,,770000]	;new PC for XJRSTF
	MOVEM	AC1,770005
MAP5:	XJRSTF	[0		;Now jump to section 1
		 1,,.+1]
	MOVSI	AC1,1		;Section 1 in return address
	HLLM	AC1,SP		;Set left half to section 1
	HLLM	AC1,(SP)	;Set left half to section 1
	POPJ	SP,		;return in section 1

DEMAP:	XJRSTF	[0		;Return to section 0
		 0,,.+1]
	HLLZ	AC1,SPLH	;Reset stack pointer
	HLLM	AC1,SP		;...
	HLLZ	AC1,STKLH	;Reset return address
	HLLM	AC1,(SP)	;...
	POPJ	SP,		;Return in section 0

	END