Description of Machine Code File Handling Routines
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] <= $AC (CO file directory flags byte) CALL SETNAM
11. Fix up the directory structure
CALL LNKFIL ; gratuitous since appending to final region...
; Save machine code program in memory into RAM file. LXI H,0 ; Remember current SP for ERRJMP DAD SP SHLD MYSTACK LXI H,ERROR SHLD ERRJMP ; Active error trap LXI H,MYFILE LXI D,FILNAM LXI B,6 CALL LDIRSB ; Copy filename to FILNAM LXI M,FILNAM+6 ; Extension MVI M,'C' INX H MVI M,'O' INX H MVI M,' ' LXI H,MYBIPA ; Format, copy in hdr LXI D,BINADR LXI B,6 CALL LDIRSB CALL LNKFIL ; Fixup directory entry start addresses CALL SRCCOM ; Search directory for a file CNZ KILCOM ; Delete if exists CALL SCNEMP ; Find an empty directory slot PUSH H ; Save the address LHLD BINTAB ; Save current BINTAB since MAKHOL damages it PUSH H LXI B,6 LHLD BINLEN PUSH H ; Save BINLEN (without header) for future use DAD B ; Add 6 bytes for header to HL MOV E,H MOV D,L ; Copy HL to DE but swap bytes??? Looks like bug... LHLD VARTAB ; Where file is created/ SHLD TEMP ; Length saved for future use CNC MAKHOL ; Make room for header and program JC OMERR ; Cleanup if out of memory XCHG LXI H,BINADR LXI B,6 CALL LDIRSB ; Copy header bytes into file LHLD BINADR ; Point to source data POP B ; Recover source length CALL LDIRSB ; Copy in the program POP H ; Restore BINTAB SHLD BINTAB POP H ; Recover dir slot pointer MVI A,$A0 ; Set type to CO XCHG LHLD TEMP ; HL <= start address of file XCHG CALL SETNAM ; Fill in dir entry CALL LNKFIL ; Fix up directory file start pointers RETURN: LXI H,0 ; Remove error trap SHLD ERRTRP RET ERROR: LHLD MYSTACK SPHL ; drop BASIC junk from stack ; put error handling code here JMP RETURN OMERR: ; Put OM error handler here JMP RETURN MYFILE: .DB "SAMPLE" MYBIPA: .DW $A000 ; Start address .DW $0800 ; Length .DW $A000 ; Entry address MYSTACK: .DB 2 TEMP: .DB 2 .END