Description of Machine Code File Handling Routines

From Bitchin100 DocGarden
Revision as of 12:10, 14 April 2009 by Jhoger (Talk | contribs)

Jump to: navigation, search

Saving a machine code program into a RAM file

In this chapter, the method to save machine code program that resides in memory into RAM file as a ".CO" file is described. In fact, the object to be saved needs not necessarily machine code program. It can be binary data. The routines described later in this chapter saved the contents of specified portion of memory exactly as they are, just appending some control information.

The control information consists of three words: load address, length, and execution address. The contents of the file is always loaded back to the location where the contents (machine code program) were located when saved. The load address in the file contains the location. Note that this is NOT the address of the file itself.

Procedure to save machine code program

To save machine code program in memory as a ".CO" file, follow the steps below. Address of individual routines used in this chapter will be described later in this document.

1. Set up file name,

Set up file name in FILNAM. This is the same step used to open an ASCII file except the extnsion should be "CO" in case of machine code program save. Body of file anme (i.e. string that precedes the extension) should be 6 characters long, space filled to the extension.

[FILNAM] <= 1st character of file name
[FILNAM+5] <= 6th character of file name
[FILNAM+6] <= "C"
[FILNAM+7] <= "O"
[FILNAM+8] <= " "

2. Set up parameters

Then set address of machine code program, its length and execution address.

[BINADR] <= Start address of binary data
[BINLEN] <= Length of binary data
[BINEXE] <= Execution start address; 0 if not executable at IPL

3. Fix up directory structure.

Refer to "Description of ROM routines in PC_8201 for detail of LNKFIL routine.

		CALL	LNKFIL		; Fix up directory structure

4. Search for the file of the same name.

Search directory for the file that has the same name as one in that we want to save the machine code program. If it exists, delete it. Obviously here you can abort without saving new one, instead of deleting old one.

		CALL	SRCCOM		; Search directory for FILNAM
		CNZ	KILCOM		; Kill old one if exist.

5. Search directory for empty (free) slot.

To register the file, make sure there's free slot in directory and remember the location of the slot. If not free slot is available, abort saving.

		CALL	SCNEMP		; Search for empty slot.
		; (save address)

6. Allocate room in RAM file.

Allocate room in RAM file for machine code program and control information (location, length, and execution address of machine code program). The length of the control information is 6 bytes long (i.e.: 3 words). MAKHOL is the routine to allocate room in [BC] length at [HL]. Here [VARTAB] tells the location where the room is to be allocated.

		[HL] <= [VARTAB]
		[BC] <= [BINLEN] + 6
		CALL	MAKHOL		; Allocate room
		JC	OMERR		; Error if out of memory

7. Copy control information

Copy control information to the top of the room allocated in above step.

8. Copy machine code program

Copy machine code program into the rest of the room.

		[HL] <= [BINADR]
		[DE] <= (Top address of the room) + 6
					; Location in RAM file where
					; the program is saved.
		[BC] <= [BINLEN]	; Length of the program.
		CALL	LDIRSB		; Do block transfer.

9. Reset BINTAB

		Special magic???
		; actually, BINTAB must be preserved across call to MAKHOL
		; because MAKHOL isn't smart enough to leave it alone
		; when opening a hole in CO file region.

10. Put file name into directory

		[HL] <= address of directory slot gained by SCNEMP
		[DE] <= address of room in RAM file. One used in MAKHOL call.
		[A] <= $AC (CO file directory flags byte)

11. Fix up the directory structure

		CALL LNKFIL		; gratuitous since appending to final region...

Sample program

	; Save machine code program in memory into RAM file.

		LXI	H,0		; Remember current SP for ERRJMP
		SHLD	ERRJMP		; Active error trap

		LXI	B,6
		CALL	LDIRSB		; Copy filename to FILNAM
		LXI	M,FILNAM+6	; Extension
		MVI	M,'C'
		MVI	M,'O'
		MVI	M,' '

		LXI	H,MYBIPA	; Format, copy in hdr
		LXI	B,6

		CALL	LNKFIL		; Fixup directory entry start addresses

		CALL	SRCCOM		; Search directory for a file
		CNZ	KILCOM		; Delete if exists

		CALL	SCNEMP		; Find an empty directory slot
		PUSH	H		; Save the address

		LHLD	BINTAB		; Save current BINTAB since MAKHOL damages it

		LXI	B,6
		PUSH	H		; Save BINLEN (without header) for future use

		DAD	B		; Add 6 bytes for header to HL

		MOV	D,L		; Copy HL to DE but swap bytes??? Looks like bug...

		LHLD	VARTAB		; Where file is created/
		SHLD	TEMP		; Length saved for future use
		CNC	MAKHOL		; Make room for header and program
		JC	OMERR		; Cleanup if out of memory

		LXI	B,6
		CALL	LDIRSB		; Copy header bytes into file