# The contents of this file have been placed into the Public Domain by its
# author and may be reused in any way whatever.
#
# Filename:	Test2.obc
# Purpose:	This is Gemini OBC code created solely for the purpose
#		of demonstrating subroutine linkages for HOP.
# Website:	http://www.ibiblo.org/apollo/Gemini.html
# Mod history:	2012-01-07 RSB	Created.
#
# The structure of this code is very simple:
#
#	At the power-up entry point (00-0-000), there's a HOP to
#	a program I call EXEC in the residual sector (17-2-000).
#
#	EXEC loops endlessly, simply calling a couple of subroutines
#	in other memory sectors, each of which does nothing but returns. 

# Tell the assembler to assume normal (rather than half-word mode) 
# memory-access mode, in memory sector 00.
		NORM
		DATA	0-00-0-000
		CODE	0-00-0-000

# Here's the execution starting point. Note that if there's a left-hand 
# symbol named "OBCENTRY" (as there is here), it's treated slightly
# specially by the assembler: extra data is embedded in the output file
# that tells the CPU emulator program to use OBCENTRY as the starting 
# address rather than using the defaults (00-0-000 or 00-2-000). In this
# example, it happens to be 00-0-000 anyway, so it doesn't really matter.
OBCENTRY	HOP	EXEC	# Jump right to the EXE program.
	
# The EXEC program is in sector 17 (the "residual" sector).	
		DATA	0-17-0-000
		CODE	0-17-2-000

# Loop endlessly.
EXEC		CLA	EXEC1	# Set up return address for subroutine SUB1.
		HOP	SUB1	# Call subroutine SUB1.
EXEC1		NOP		# Returns to here. (Doesn't have to be NOP!)
		CLA	EXEC2	# And repeat for subroutine SUB2.
		HOP	SUB2
EXEC2		NOP
		TRA	EXEC	# Loop again ...	

# Subroutine SUB1 is in sector 05
		DATA	0-05-0-000
		CODE	0-05-2-000
		
RSUB1				# Variable to store the return address.		
SUB1		STO	RSUB1	# Store the return address.
		NOP		# Execute some instructions ...
		HOP	RSUB1	# Return from the subroutine.
		
# Subroutine SUB2 is in sector 07.  This subroutine is the 
# same as SUB1.
		DATA	0-07-0-000
		CODE	0-07-2-000
		
RSUB2				# Variable to store the return address.		
SUB2		STO	RSUB2	# Store the return address.
		NOP		# Execute some instructions.
		HOP	RSUB2	# Return from the subroutine.