[Image] Z80 Assembler/Disassembler
Z80 Disassembler
I created this small disassembler for a Z80 cpu at one afternoon. It is a
commandline tool. The size of the ROM and entry points have to be coded
directly in the sourcecode.
Every ANSI C compiler should compile this program. It is tested with Think
C 5.0 on a Macintosh. It only uses come ANSI functions (look into main())
for loading a file called "EPROM".
The program has two parts:
1. Analyze the code. The disassembler tries to analyze what part of the
binary data is program code and what part is data. It start with all
hardware vectors of the Z80 (RST opcodes, NMI) and parses all jumps
via a recursive analyze via ParseOpcode(). Every opcode is marked in
an array (OpcodesFlags). There are some exceptions, the parser can't
recognize:
1. self modifying code. A ROM shouldn't contain such code.
2. calculated branches with JP (IY), JP (IX) or JP (HL). The parser
can't recognize them, either. On a Macintosh the low-level
debugger is called, when such a jump is found. Set the Symbol
DEBUGGER to 0 to disable this behavior...
3. Jumptables. These are quite often in a ROM. Only solution:
disassemble the program and look into the code. If you found a
jumptable - like on my Futura aquarium computer - insert some
more calls of ParseOpcodes().
4. Unused code. Code that is never called by anybody, could not be
found. Make sure that the code is not called via a jump table!
2. Disassembly of the code. With the help of the OpcodesFlags table the
disassembler now creates the output. This subroutine is quite long. It
disassembles one opcode at a specific address in ROM into a buffer. It
is coded directly from a list of Z80 opcodes, so the handling of IX
and IY could be optimized quite a lot.
The subroutine OpcodeLen() returns the size of one opcode in bytes. It is
called while parsing and while disassembling.
The disassembler recognizes no hidden opcodes (the assembler does!). I
didn't had a table for them while writing the disassembler and they were
not needed anyway.
If a routine wanted an "address" to the Z80 code, it is in fact an offset
to the array of code. No pointers! Longs are not necessary for a Z80,
because the standard Z80 only supports 64k.
In main() is a switch for disassembly with address and hexdump instead of
disassembly with labels. This is useful for findings bugs in the
disassembler and creating a list of variables.
This program is freeware. It is not allowed to be used as a base for a
commercial product!
Z80 Assembler
I created the assembler for the Z80 a few days later to compile the changes
code from the disassembler into an EPROM image and build a new firmware for
my aquarium computer. I needed almost two days for the assembler, this
means: commandline only... If you want to change the filename of the
sourcefile, you have to change main().
This small assembler has some nice gadgets: it is a quite fast tokenizing
single-pass assembler with backpatching. It knows all official Z80 opcodes
and some undocumented opcodes (mainly with IX and IY). The Z80 syntax is
documented in the Zilog documentation.
The assembler allows mathematical expressions in operands: +, -, *, /, %
(modulo), & (and), | (or), ! (not), ^ (xor), << (shift left) and >> (shift
right). Brackets are also available. The expression parser is located in
Z80 Calc.c. Number can be postpended by a D, H or B for decimal,
hexadecimal and binary numbers.
The assembler also knows the most commend pseudo opcodes (look into the
sourcefile Z80 Tokenize.c):
;
This line is a comment.
IF
Start the conditional expression. If false, the following sourcecode
will be skipped (until ELSE or ENDIF).
ELSE
End of the condition expression.
ELSE
Include the following code, when the expression on IF was false.
END
End of the sourcecode. The assembler stops here. Optional.
ORG
Set the PC in the 64k address space. E.g. to generate code for address
$2000.
PRINT
Print the following text on the console. Great for testing the
assembler.
EQU or =
Set a variable.
DEFB
Put a byte at the current address
DEFW
But a word at the current address (little endian!)
DEFM
But several bytes in the memory, starting at the current address.
Seperated with a "," or a string.
DEFS
Set the current address n bytes ahead. Defines space for global
variables that have no given value.
The current version
* Z80.sit
(
geocities.com/tutorman_2000)