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Trailing-Edge - PDP-10 Archives - bb-h138f-bm - 7-sources/mem.mac
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TITLE MEM -- Memory allocator for the RTL

;
;	COPYRIGHT (C) DIGITAL EQUIPMENT CORPORATION 1984, 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.
;
SUBTTL Edit History

; Version 1.0

; Version 1.1

;.EDIT 50	Formally go to version 1.1, update copyright, insert V1.1
;			development changes (formally V2)
;		DDB,15-Jan-85,SPR:NONE

SALL

SEARCH DDBSYM, DYNSYM, MONSYM, MACSYM

EXTERNAL RTLERR

SEGMENT DATA

; Memory management concepts

; This memory manager manages several contiguous chunks of memory.  Each
; request for allocation must specify which chunk it wishes to allocate from.
; Chunks may be bigger or smaller than sections, and may (obviously) cross
; section boundaries.  Pieces allocated may reside anywhere within the chunk.

; On deallocation, adjacent free blocks are merged together using Kunth's
; algorithm as liberally interpreted by several people.

; A block of memory is a structured entity.  It has a header, a body, and
; a trailer.  Only the body is available to users.  The "address" of the 
; block is the address of the first word of the body.

; Chunks are identified by their index into the chunk tables below.
; No real chunk may start at 0,,0; this is used to identify an empty slot.

CNKMAX==:50			;How many chunks can we manage?

RT.CKS:: BLOCK CNKMAX		;Table of chunk start information
RT.CKE:: BLOCK CNKMAX		;Table of chunk end information
SUBTTL Chunks

; Error chunk -- used for allocating error-processing blocks only, in hopes
; that we won't run out while processing an error
ERCNKS:: BLOCK 500
ERCNKE==:.-1

; RTL chunk -- eventually this should be figured out from the LINK memory
; map, but for now it's a static allocation at compile time.
RTCNKS:: BLOCK 200K
RTCNKE==:.-1
SUBTTL ME$ALM -- Allocate memory

; This will allocate a block of memory from the specified chunk and return
; its address, or return an error indicating that this is not possible.

; Arguments:
;	1/	Chunk number
;	2/	Size of block desired

; Return values:
;	1/	Chunk number
;	2/	Address of block allocated.

; Preserves registers 6-17

; Register usage:
;	P1/	ID of chunk requested
;	P2/	Current block address

SEGMENT CODE

ME$ALM::
	PUSH P, P1
	PUSH P, P2
	PUSH P, T1		;Save chunk number too

	MOVE P1, T1

	MOVE P2, RT.CKS(P1)	;Address of chunk
	ADDI P2, .MBHLN		;Address of first block in chunk

ALM001:	MOVE T1, .MBDES(P2)	;Get the descriptor word from header
	TXNE T1, MB%ALO		;Skip if not allocated
	    JRST ALMNXB		;Go on to next block, than

; We are now looking at a free block.  Decide if it suits us.
	TXZ T1, ^-MB%LEN	;Extract length (must be at LO end of word!)
	CAMGE T1, T2		;Skip if this block at least big enough
	    JRST ALMNXB		;Go on to next block

; Timing window here.  We mark whole block as allocated, but something
; could happen between the MOVE at ALM001 and now.  Any ideas?
	MOVX T0, MB%ALO
	IORM T0, .MBDES(P2)	;Set whole block allocated

; The block we are looking at (P2) is big enough (length in T1).
; Time to get out the big knives!  Or is it?
	MOVE T3, T1
	SUB T3, T2		;Compute what's left of block
	CAIG T3, .MBOVH		;Will there be a body to what's left?
	  JRST ALMDON		;Give caller full block

; Split the free block.  Results will be used block and residual block.
; P2 holds free block address.
; T1 holds free block length.  
; T2 holds length requested for used block.

	MOVE T3, P2
	ADD T3, T1		;T3 holds free block trailer address
	MOVE T4, P2
	ADD T4, T2		;T4 holds used block trailer address
	MOVE T5, T4
	ADDI T5, .MBOVH		;T5 holds free block address

	; The order of this is critical to minimize timing windows.  Note
	; that memory will often be allocated and freed at interrupt level,
	; so this can be kind of interesting.  In fact, this has windows in
	; it if you allocate and then free a small block at interrupt level
	; fast enough (it could get the residual block and then return it
	; before the trailer on the used block is set up).

	MOVEM P2, .MBADR(T4)	;Set trailer on what will be used block
	MOVE T4, .MBDES(P2)	;Get header on original block

	MOVE T0, T1
	SUB T0, T2
	SUBI T0, .MBOVH		;Compute length left for residual block
;	TXZ T0, MB%ALO		;Residual block is not allocated (word was
				;clear, so don't bother to clear it again)
	TXNE T4, MB%END		;Skip if end bit clear
	  TXO T0, MB%END	;Set end bit
	MOVEM T0, .MBDES(T5)	;Set header on what will be residual block

	MOVEM T5, .MBADR(T3)	;Set trailer on residual block

	TXO T2, MB%ALO		;Used block is allocated
	TXNE T4, MB%BEG		;Skip if begin bit clear
	  TXO T2, MB%BEG	;Set begin bit
	MOVEM T2, .MBDES(P2)	;Set header on used block

	JRST ALMDON		;Done.  Address of block is in P2

; No luck so far.  Look at next block.
ALMNXB:	MOVE T1, .MBDES(P2)
	TXZ T1, ^-MB%LEN	;Mask to get length
	ADD P2, T1
	ADDI P2, .MBOVH		;Now have address of next block
	CAMGE P2, RT.CKE(P1)	;Skip if this hypothetical block is past
				;end of chunk
	    JRST ALM001		;Go see if maybe we can allocate this

; If we fall through to here, caller loses: no such block available.
	POP P, T0		;Restore chunk number
	POP P, P2
	POP P, P1		;Restore preserved registers
	PUSH P, T0		;Chunk requested
	PUSH P, T2		;Length requested
	PUSH P, [2]		;Arg count
	PUSH P, [ME$IMC]	;Condition
	JRST RTLERR		;Standard RTL error handling

; Successful completion
ALMDON:	
; Zero what will become body of used block
	MOVE T0, .MBDES(P2)
	TXZ T0, ^-MB%LEN
	MOVE T4, P2
	ADD T4, T0		;Calculate address of trailer
	SETZM 0(P2)		;Zero first word of body of used block
	XMOVEI T0, 0(P2)
	HRL T0, T0
	AOS T0			;Now have first,,second in T1
	BLT T0, -.MBTLN(T4)	;ZERO THE BLOCK


	MOVE T2, P2		;Return block address in T2
	POP P, T1		;Restore chunk number
	POP P, P2
	POP P, P1		;Restore preserved registers
	RET
SUBTTL ME$DLM -- Deallocate a block of memory

; This frees a block allocated with ME$ALM

; Arguments:
;	1/	Address of the block

; Preserves registers 6-17

; Register usage:
;	T4/	Address of the block we are freeing

ME$DLM::
	MOVE T4, T1		;Address of the block of memory
	MOVE T0, .MBDES(T4)	;Get descriptor for this block
	TXNN T0, MB%ALO		;Skip if it's marked as allocated
	    JRST DLMNAL		;Invalid -- block not allocated!

; Try to merge this block with a possible previous free block
	TXNE T0, MB%BEG		;Skip if this block not the beginning
	    JRST DLMNXT		;Well, go try to merge with following block

	XMOVEI T2, -.MBOVH(T4)	;Get address of previous trailer in T2
	MOVE T1, .MBADR(T2)	;Get address of header in T1
	MOVE T3, .MBDES(T1)	;Get descriptor of this block
	TXNE T3, MB%ALO		;Skip if this block also free
	    JRST DLMNXT		;Previous not free, try next

; T1 points to header of previous free block.  T2 points to trailer.
; T4 points to header of new free block.
; T0 contains descriptor of new free block.
; Merge these two together

	TXZ T0, ^-MB%LEN	;Mask to extract length (already rjust)
	MOVE T2, T4		;Adress of header of new free block
	ADD T2, T0		;Address of new free block trailer in T2
	MOVEM T1, .MBADR(T2)	;Trailer of combined block points to header of
	ADDI T0, .MBOVH		;Total size of new free block (including ovh)
	ADDM T0, .MBDES(T1)	;Update total size of block
	; Previous free block must already be free
	MOVE T0, .MBDES(T4)	;Get new free block descriptor
	TXZ T0, ^-MB%END	;Mask to just END bit
	IORM T0, .MBDES(T1)	;Set end bit in previous free if set in new
	MOVE T4, T1		;Now the "new free block" is the merged blocks
	; Fall through to DLMNXT and try to merge with following block

; Attempt to merge new free block with following block (if any)
; T4 holds address of new free block
DLMNXT:	MOVE T0, .MBDES(T4)	;Get descriptor of new free block
	TXZ T0, MB%ALO		;This block will now be free
	MOVEM T0, .MBDES(T4)
	TXNE T0, MB%END		;Skip if new block not last block
	  JRST DLMDON		;Done, no next block

; There is a following block we can consider merging with...
	MOVE T1, T4		;Address of new block
	TXZ T0, ^-MB%LEN	;Get block size (already rjust)
	ADD T1, T0		;Address of new block trailer
	MOVE T2, T1
	ADDI T2, .MBOVH		;Address of next block
	MOVE T3, .MBDES(T2)	;Get next block descriptor
	TXNE T3, MB%ALO		;Skip if next block is free
	  JRST DLMDON		;Done, next block isn't free

; There is a free next block to merge with.  Do it.
; T4 is address of new block.  
; T2 is address of next block
; T3 is descriptor of next block
	MOVE T1, .MBDES(T4)	;Get descriptor of new block
	TXNE T3, MB%END		;Skip if next block not last
	  TXO T1, MB%END	;Combined block will be last
	TXZ T1, MB%ALO		;Combined block won't be allocated
	TXZ T3, ^-MB%LEN	;Get length of next block
	ADD T1, T3		;Increase length of combined block
	ADDI T1, .MBOVH		;Include overhead words
	MOVEM T1, .MBDES(T4)	;Put back descriptor of combined block
	ADD T2, T3		;Get address of next block trailer
	MOVEM T4, .MBADR(T2)	;Put combined block trailer at end

; Done!!!
DLMDON:	RET			;No register save was necessary

; Serious error -- block to return wasn't flagged as allocated
DLMNAL:	PUSH P, T4		;Block being returned
	PUSH P, [1]		;Arg count
	PUSH P, [ME$NAL]	;Condition
	JRST RTLERR		;Standard RTL error handling (no return)
SUBTTL ME$MEM -- Chunk initialization

; Call this routine to initialize a chunk.  This is particularly for
; use by MASTER INIT.

; Arguments:
;	T1/	Chunk start address
;	T2/	Chunk end address

; Returns:
;	T3/	Chunk ID

; Errors:
;	ME$NCA	No chunk available

; Trashes T0-T3

ME$MEM::
	MOVX T3, 0
MEM001:	CAIL T3, CNKMAX
	  JRST MEMLOS		;No chunk ID available
	SKIPE RT.CKS(T3)	;Skip if chunk is free
	  AOJA T3, MEM001	;Loop
	
	MOVEM T1, RT.CKS(T3)
	MOVEM T2, RT.CKE(T3)

; Now initialize one free block which fills the chunk
	ADDI T1, .MBHLN		;Get block address given chunk address
	MOVE T0, T2
	SUB T0, T1
	SUBI T0, .MBTLN-1	;Compute block length
	TXO T0, MB%BEG!MB%END	;Both first and last block in chunk
	;TXZ T0, MB%ALO		;It's already not allocated, no work to do
	MOVEM T0, .MBDES(T1)	;Put away descriptor word
	MOVEM T1, .MBADR(T2)	;Put away trailer word
	MOVE T1, T3		;Return chunk ID
	RET

; Lose big -- no chunk ID's available
MEMLOS:
	PUSH P, T1
	PUSH P, T2
	PUSH P, [2]		;Arg count
	PUSH P, [ME$NCA]
	JRST RTLERR
SUBTTL ME$DMC -- Dump a chunk of memory

; This is intended for use during debugging of user programs, or of
; the memory allocator itself.

; Arguments:
;	T1/	Chunk number

; Preserves registers 6-17

ME$DMC::
	PUSH P, P1
	PUSH P, P2

	MOVE P1, RT.CKS(T1)
	MOVE P2, RT.CKE(T1)

	TMSG <
********** Dumping chunk from >
	MOVX T1, .PRIOU
	MOVE T2, P1
	MOVX T3, <NO%MAG!FLD(^D8,NO%RDX)>
	NOUT%
	  ERJMP .+1

	TMSG < to >
	MOVX T1, .PRIOU
	MOVE T2, P2
	MOVX T3, <NO%MAG!FLD(^D8,NO%RDX)>
	NOUT%
	  ERJMP .+1
	TMSG <
>
	ADDI P1, .MBHLN		;Address of first block in chunk

DMC001:	TMSG <Block at >
	MOVX T1, .PRIOU
	MOVE T2, P1
	MOVX T3, <NO%MAG!FLD(^D8,NO%RDX)>
	NOUT%
	  ERJMP .+1		;No finesse in debugging routines
	TMSG < length >
	MOVX T1, .PRIOU
	MOVE T2, .MBDES(P1)
	TXZ T2, ^-MB%LEN
	MOVX T3, <NO%MAG!FLD(^D8,NO%RDX)>
	NOUT%
	  ERJMP .+1
	MOVE T2, .MBDES(P1)
	MOVX T1, <-1,,[ASCIZ / is FREE/]>
	TXNN T2, MB%ALO
	  PSOUT%
	TMSG <
>
	MOVX T1, <-1,,[ASCIZ /    FIRST block in chunk
/]>
	TXNE T2, MB%BEG
	  PSOUT%
	MOVX T1, <-1,,[ASCIZ /    LAST block in chunk
/]>
	TXNE T2, MB%END
	  PSOUT%
	MOVE T4, P1
	MOVE T0, .MBDES(P1)
	TXZ T0, ^-MB%LEN
	ADD T4, T0		;Trailer address in T4
	CAMN P1, .MBADR(T4)	;Skip if trailer doesn't point at block
	  JRST DMCNXT		;OK
	TMSG <   *TRAILER address INCORRECT: >
	MOVX T1, .PRIOU
	MOVE T2, .MBADR(T4)
	MOVX T3, <NO%MAG!FLD(^D8,NO%RDX)>
	NOUT%
	  ERJMP .+1
	TMSG <
>

DMCNXT:	ADDI T4, .MBOVH		;Address of next block
	MOVE P1, T4
	CAMG P1, P2		;Skip if this block past end of chunk
	  JRST DMC001		;Loop to dump all blocks in chunk

; Done
	TMSG <********** End of chunk dump

>
	POP P, P2
	POP P, P1
	RET
SUBTTL Routine stubs for routines not yet implemented

SEGMENT CODE

ME$ALS::
ME$ALP::
ME$DLS::
ME$DLP::
	PUSH P, 0(P)		;Duplicate return address
	PUSH P, [1]		;Arg count
	PUSH P, [DY$NYI]	;Condition
	JRST RTLERR

	END