# Copyright:	Public domain.
# Filename:	THROTTLE_CONTROL_ROUTINES.agc
# Purpose: 	Part of the source code for Luminary 1A build 099.
#		It is part of the source code for the Lunar Module's (LM)
#		Apollo Guidance Computer (AGC), for Apollo 11.
# Assembler:	yaYUL
# Contact:	HARTMUTH GUTSCHE <hgutsche@xplornet.com>.
# Website:	www.ibiblio.org/apollo.
# Pages:	793-797
# Mod history:	2009-05-20 HG	Transcribed from page images.
#
# This source code has been transcribed or otherwise adapted from
# digitized images of a hardcopy from the MIT Museum.  The digitization
# was performed by Paul Fjeld, and arranged for by Deborah Douglas of
# the Museum.  Many thanks to both.  The images (with suitable reduction
# in storage size and consequent reduction in image quality as well) are
# available online at www.ibiblio.org/apollo.  If for some reason you
# find that the images are illegible, contact me at info@sandroid.org
# about getting access to the (much) higher-quality images which Paul
# actually created.
#
# Notations on the hardcopy document read, in part:
#
#	Assemble revision 001 of AGC program LMY99 by NASA 2021112-61
#	16:27 JULY 14, 1969

# Page 793
		BANK	31
		SETLOC	FTHROT
		BANK
		EBANK=	PIF
		COUNT*	$$/THROT

# * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
# HERE FC, DESIRED THRUST, AND FP, PRESENT THRUST, UNWEIGHTED, ARE COMPUTED.

THROTTLE	CA	ABDELV		# COMPUTE PRESENT ACCELERATION IN UNITS OF
		EXTEND			# 2(-4) M/CS/CS, SAVING SERVICER TROUBLE
		MP	/AF/CNST
 +3		EXTEND
 		QXCH	RTNHOLD
AFDUMP		TC	MASSMULT
		DXCH	FP		# FP = PRESENT THRUST
		EXTEND
		DCA	/AFC/
		TC	MASSMULT
		TS	FC		# FC = THRUST DESIRED BY GUIDANCE
		DXCH	FCODD		# FCODD = WHAT IT IS GOING TO GET

# IF IT HAS BEEN LESS THAN 3 SECONDS SINCE THE LAST THROTTLING, AUGMENT FP USING THE FWEIGHT CALCULATED THEN.

		CS	TTHROT		# THIS CODING ASSUMES A FLATOUT WITHIN
		AD	TIME1		#   80 SECONDS BEFORE FIRST THROTTLE CALL
		MASK	POSMAX
		COM
		AD	3SECS
		EXTEND
		BZMF	WHERETO		# BRANCH IF (TIME1-TTHROT +1) > 3 SECONDS
		EXTEND
		DCA	FWEIGHT
		DAS	FP

# THIS LOGIC DETERMINES THE THROTTLING IN THE REGION 10% - 94%.  THE MANUAL THROTTLE, NOMINALLY SET AT
# MINIMUM BY ASTRONAUT OR MISSION CONTROL PROGRAMS, PROVIDES THE LOWER BOUND.  A STOP IN THE THROTTLE HARDWARE
# PROVIDES THE UPPER.

WHERETO		CA	EBANK5		# INITIALIZE L*WCR*T AND H*GHCR*T FROM
		TS	EBANK		#   PAD LOADED ERASABLES IN W-MATRIX
# Page 794
		EBANK=	LOWCRIT
		EXTEND
		DCA	LOWCRIT
		DXCH	L*WCR*T
		CA	EBANK7
		TS	EBANK
		EBANK=	PIF
		CS	ZERO		# INITIALIZE PIFPSET
		TS	PIFPSET
		CS	H*GHCR*T
		AD	FCOLD
		EXTEND
		BZMF	LOWFCOLD	# BRANCH IF FCOLD < OR = HIGHCRIT
		CS	L*WCR*T
		AD	FCODD
		EXTEND
		BZMF	FCOMPSET	# BRANCH IF FC < OR = LOWCRIT
		CA	FP		# SEE NOTE 1
		TCF	FLATOUT1

FCOMPSET	CS	FMAXODD		# SEE NOTE 2
		AD	FP
		TCF	FLATOUT2

LOWFCOLD	CS	H*GHCR*T
		AD	FCODD
		EXTEND
		BZMF	DOPIF		# BRANCH IF FC < OR = HIGHCRIT

		CA	FMAXPOS		# NO:  THROTTLE-UP
FLATOUT1	DXCH	FCODD
		CA	FEXTRA
FLATOUT2	TS	PIFPSET

# NOTE 1	FC IS SET EQUAL TO FP SO PIF WILL BE ZERO.  THIS IS DESIRABLE
#		AS THERE IS ACTUALLY NO THROTTLE CHANGE.
#
# NOTE 2	HERE, SINCE WE ARE ABOUT TO RETURN TO THE THROTTLEABLE REGION
#		(BELOW 55%) THE QUANTITY -(FMAXODD - FP) IS COMPUTED AND PUT
#		INTO PIFPSET TO COMPENSATE FOR THE DIFFERENCE BETWEEN THE
#		NUMBER OF BITS CORRESPONDING TO FULL THROTTLE (FMAXODD) AND THE
#		NUMBER CORRESPONDING TO ACTUAL THRUST (FP).  THUS THE TOTAL
#		THROTTLE COMMAND PIF = FC - FP - (FMAXODD - FP) = FC - FMAXODD.

DOPIF		TC	FASTCHNG
		EXTEND
		DCA	FCODD
		TS	FCOLD
		DXCH	PIF
		EXTEND
# Page 795
		DCS	FP
		DAS	PIF		# PIF = FC - FP, NEVER EQUALS +0

DOIT		CA	PIF
		AD	PIFPSET		# ADD IN PIFPSET, WITHOUT CHANGING PIF
		TS	PSEUDO55
		TS	THRUST
		CAF	BIT4
		EXTEND
		WOR	CHAN14
		CA	TIME1
		TS	TTHROT

# SINCE /AF/ IS NOT AN INSTANTANEOUS ACCELERATION, BUT RATHER AN "AVERAGE" OF THE ACCELERATION LEVELS DURING
# THE PRECEEDING PIPA INTERVAL, AND SINCE FP IS COMPUTED DIRECTLY FROM /AF/, FP IN ORDER TO CORRESPOND TO THE
# ACTUAL THRUST LEVEL AT THE END OF THE INTERVAL MUST BE WEIGHTED BY
#
# 	          PIF(PPROCESS + TL)     PIF /PIF/
#	FWEIGHT = ------------------ + -------------
#		       PGUID           2 PGUID FRATE
#
# WHERE PPROCESS IS THE TIME BETWEEN PIPA READING AND THE START OF THROTTLING, PGUID IS THE GUIDANCE PERIOD, AND
# FRATE IS THE THROTTLING RATE (32 UNITS PER CENTISECOND).  PGUID IS EITHER 1 OR 2 SECONDS.  THE "TL" IN THE
# FIRST TERM REPRESENTS THE ENGINE'S RESPONSE LAG.  HERE FWEIGHT IS COMPUTED FOR USE NEXT PASS.

		CA	THISTPIP +1		# INITIALIZE FWEIGHT COMP AS IF FOR P66
		TS	BUF

		CS	MODREG			# ARE WE IN FACT IN P66?
		AD	DEC66
		EXTEND
		BZF	FWCOMP			# YES

		CA	PIPTIME +1		# NO:  INITIALIZE FOR TWO SECOND PERIOD
		TS	BUF
		CAF	4SECS
		TCF	FWCOMP +1

FWCOMP		CAF	2SECS
 +1		TS	Q
 		EXTEND
		MP	BIT6
		LXCH	BUF +1
		CS	BUF		# TIME OF LAST PIPA READING.
		AD	TIME1
		AD	THROTLAG	# COMPENSATE FOR ENGINE RESPONSE LAG
		MASK	LOW8		# MAKE SURE SMALL AND POSITIVE
		ZL
		EXTEND
# Page 796
		DV	Q
		EXTEND
		MP	PIF
		DOUBLE
		DXCH	FWEIGHT
		CCS	PIF
		AD	ONE
		TCF	+2
		AD	ONE
		EXTEND
		MP	PIF
		EXTEND
		DV	BUF +1
		ZL
		DAS	FWEIGHT

THDUMP		TC	RTNHOLD

# FLATOUT THROTTLES UP THE DESCENT ENGINE, AND IS CALLED AS A BASIC SUBROUTINE.

FLATOUT		CAF	BIT13		# 4096 PULSES
WHATOUT		TS	PIFPSET		# USE PIFPSET SO FWEIGHT WILL BE ZERO
		CS	ZERO
		TS	FCOLD
		TS	PIF
		EXTEND
		QXCH	RTNHOLD
		TCF	DOIT

# MASSMULT SCALES ACCELERATION, ARRIVING IN A AND L IN UNITS OF 2(-4) M/CS/CS, TO FORCE IN PULSE UNITS.

MASSMULT	EXTEND
		QXCH	BUF
		DXCH	MPAC
		TC	DMP
		ADRES	MASS
		TC	DMP		# LEAVES PROPERLY SCALED FORCE IN MPAC
		ADRES	SCALEFAC
		TC	TPAGREE
		CA	MPAC
		EXTEND
		BZF	+3
		CAF	POSMAX
		TC	BUF
		DXCH	MPAC +1
		TC	BUF
# Page 797
# CONSTANTS:-

FEXTRA		=	BIT13		# FEXT +5.13309020E+ 4

/AF/CNST	DEC	.13107

# * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
