.TITLE	CB
	.IDENT	/850604/
	.ENABL	LC
	.SBTTL	Abstract
;
;
;
;	K E R N E L   C O N T R O L   B L O C K S
;
;
;
; 	Title		Control Blocks
;	Author(s)	John Sloan, David Hemmendinger, et al.
;	Installation	Wright State University
;			Departments of Computer Science/Computer Engineering
;	Date		Spring, 1982
;	Language	Macro-11
;	Abstract
;
;			This module is the impure portion of the kernel.
;			It contains the various kernel data structures such
;			as the Current Process pointer, the READY queue, and
;			the pool of Free PCBS.
;
;			See the comments accompanying the kernel for more
;			information.
;
;			This software is in the public domain provided
;			credit is acknowledged to the Computer Science
;			Department of Wright State University. No warranty
;			is expressed or implied by the authors, the department,
;			or the University.
;
;	Modifications
;
;		JLS 		Eliminated buffer pool and associated symbolics
;		JLS	06Jun84	Improved embedded documentation
;		DH		Placed CB in program section labelled DATA
;		JLS	29Jan85	Introduced pseudo-C code
;		DH/JLS	12Mar85	More finicky changes
;
	.PSECT	DATA,RW,D

	.SBTTL	Global Definitions
;------------------------------------------------------------------------------
;
;
;	G L O B A L   D E F I N I T I O N S
;
;
;------------------------------------------------------------------------------
;
	.GLOBL	P.NEXT,P.STACK,P.PC,P.PS,P.SP,P.BYTES,P.WORDS
	.GLOBL	Q.NUM,Q.SLOTS,Q.FRONT,Q.REAR,Q.SEMA,Q.BYTES,Q.WORDS
	.GLOBL	N.PCBS.N.VARS
	.GLOBL	STACK,CP,READY,PCBS,FPCBS
	.SBTTL	Symbolic Definitions
;------------------------------------------------------------------------------
;
;
;	S Y M B O L I C   D E F I N I T I O N S
;
;
;
;	Allocation Definitions
;
;		To alter the number of PCBs, the size of the initial boot
;		stack, or the size of each PCB stack: edit the appropriate
;		line, reassemble this module, and relink the application.
;
;------------------------------------------------------------------------------
;
	N.PCBS	=	10.			; NUMBER OF PCBS IN SYSTEM
	N.BOOT	=	32.			; NUMBER OF WORDS IN BOOT STACK
	N.STACK	=	28.			; NUMBER OF WORDS IN PCB STACK

	.SBTTL	Process Control Block Definitions
;------------------------------------------------------------------------------
;
;	Process Control Block Definitions
;
;		+-----------------------+
;	PCB:	|	P.NEXT		|	pointer to next PCB in a queue
;		+-----------------------+
;		|	P.PC		|	entry point of process
;		+-----------------------+
;		|	P.PS		|	CPU priority of process
;		+-----------------------+
;		|	P.SP		|	saved stack pointer
;		+-----------------------+
;		|	:		|
;		|	:		|
;		=	N.STACK words	=	process' own stack
;		|	:		|
;		|	:		|
;		+-----------------------+
;			P.STACK			base of stack
;
;	typedef	struct pcb	{
;				pcb *next;
;				PROCESS (*pc)();
;				int ps;
;				LONG sp;
;				LONG stack[NSTACK];
;				} PCB;
;					
;------------------------------------------------------------------------------
;
	P.NEXT	=	0			; LINK TO NEXT PCB
	P.PC	=	2			; PROCESS ENTRY POINT
	P.PS	=	4			; PROCESS PROCESSOR STATUS
	P.SP	=	6			; SAVED STACK POINTER
	P.STACK	=	<P.SP+2+<N.STACK*2>>	; BOTTOM OF STACK
	P.BYTES	=	P.STACK			; PCB SIZE IN BYTES
	P.WORDS	=	<P.BYTES/2>		; PCB SIZE IN WORDS
	.SBTTL	Queue Header Definitions
;------------------------------------------------------------------------------
;
;	Queue Header Definitions
;
;		+-----------------------+
;	QUEUE:	|	Q.NUM		|	number of items in queue
;		+-----------------------+
;		|	Q.SLOTS		|	number of available slots
;		+-----------------------+
;		|	Q.FRONT		|	link to first item in queue
;		+-----------------------+
;		|	Q.REAR		|	link to last item in queue
;		+-----------------------+
;			Q.SEMAPHORE		beginning of semaphore
;
;	typedef struct	{
;			int num, slots;
;			char *front, *rear;
;			} QUEUE;
;
;	typedef QUEUE SEMAPHORE;
;
;	typedef struct	{
;			QUEUE queue;
;			SEMAPHORE semaphore;
;			} MAILBOX;
;
;------------------------------------------------------------------------------
;
	Q.NUM	=	0			; NUMBER OF ITEMS IN QUEUE (<0)
	Q.SLOTS	=	2			; NUMBER OF EMPTY SLOTS IN QUEUE (>0)
	Q.FRONT	=	4			; LINK TO FIRST ITEM IN QUEUE
	Q.REAR	=	6			; LINK TO LAST ITEM IN QUEUE
	Q.SEMAP	=	10			; SEMAPHORE (IF MESSAGE QUEUE)
	Q.BYTES	=	8.			; SIZE OF HEADER IN BYTES
	Q.WORDS	=	<Q.BYTES/2>		; SIZE OF HEADER IN WORDS

	.SBTTL	Storage Areas
	.SBTTL	Boot Stack
;------------------------------------------------------------------------------
;
;
;
;	S T O R A G E   A R E A S
;
;
;
;	Boot Stack
;
;		This stack is only used when the kernel first initializes. Once
;		multitasking begins, the stacks in the Process Control Blocks
;		are used exclusively.
;
;		LONG stack[NBOOT];
;
;------------------------------------------------------------------------------
;

	.BLKW	N.BOOT				; USED ONLY AT INITIALIZATION
STACK:
	.SBTTL	Current Process Pointer
;------------------------------------------------------------------------------
;
;	Current Process Pointer
;
;		This points to the Process Control Block of the Current
;		Process, that is, the process that currently has control
;		of the CPU.
;
;		PCB *cp;
;
;------------------------------------------------------------------------------
;
CP:	.BLKW	1				; LINK TO CURRENT (RUNNING) PCB
;
	.SBTTL	Ready Queue
;------------------------------------------------------------------------------
;
;	Ready Queue
;
;		This is a queue that contains Process Control Blocks of
;		all processes that are READY to run but do not currently
;		have control of the CPU.
;
;		QUEUE ready;
;
;------------------------------------------------------------------------------
;
READY:	.BLKW	Q.WORDS				; QUEUE OF READY_TO_RUN PCBS
;
	.SBTTL	Free Process Control Block Pool
;------------------------------------------------------------------------------
;
;	Free Process Control Block Pool
;
;		This is the kernel's pool of unused Process Control Blocks.
;		PCBs are removed from this pool by CRP and returned to it by
;		EOP.
;
;		MAILBOX pcbs;
;		PCB fpcbs[NPSBS];
;
;------------------------------------------------------------------------------
;
PCBS:	.BLKW	<2*Q.WORDS>			; POOL OF FREE (UNUSED) PCBS
FPCBS:	.BLKW	<N.PCBS*P.WORDS>		; ALLOCATION OF FREE PCBs

	.SBTTL	End
;------------------------------------------------------------------------------
;
;
;	E N D   O F   C O N T R O L   B L O C K S
;
;
;------------------------------------------------------------------------------
;
	.END