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shazzam

Not your daddy's C64 cross-assembler... :)

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What is shazzam?

It is probably easier to say what shazzam is NOT:

  • a new 6502 cross-assembler (it relies on existing ones)
  • a python compiler for 6502
  • some kind of Micro-Python or Circuit-Python implementation

And where it took its inspiration from multiple famous C64 tools:

  • KickC: a Kiss Assembler code generator using a subset of C language.
  • C64jasm: a Cross Assembler supporting inline extensions using pure Javacript.
  • Bass: an ACME-like cross assembler using Lua for scripting and internal emulator for testing.
  • Sparkle: an IRQ Loader managing on time loading of data and code segments.
  • Raistlin's C++ code generator: Raistlin/G*P's top secret framework to code awesome demos.

As a result, by using all those great modern C64 Development tools, I found out that state of the art demo effects are mostly based on code generation, most of the time using cross-assembler macros and external tools.

So the usage of non assembler tooling became more important than the assembly code itself, that's why I thought that "reversing" the cross assembler idea (meaning providing a good but basic cross-assembler with quite powerful, complex and more or less standard macro language) would make sense: don't extend the cross assembler with some kind of complex scripting language but extend existing high level languages with simple assembler capabilities.

This is the magic of shazzam, write Python code as usual, to process your images, create your lookup tables, read your SID files.... no limit to your creativity then, generate the assembly code required to use this data as you would do with the cross-assembler.

Features in brief

  • Python code generator for official and illegal 6502 instructions
  • Generate cc65 or c64jasm assembly code from your Python application in real-time
  • 6502 emulator to write unit tests and debug step-by-step routines
  • Pre-integrated packers (Exomizer, Apultra, zx7...) for incbin and prg
  • Export Sparkle compatible script (D64 generation available on Windows only)
  • Plugins to load and parse SID, SPD, KLA files
  • Support multi-files, multi-segments
  • Segment optimizer to maximize contiguous memory usage
  • Support VASYL opcodes for BeamRacer expansion card
  • Rasterline cycles simulation to race the beam
  • Simple disassembler
  • Integrate well in any Python and 6502 assembly code compatible IDE. (Visual code works great)
  • OS agnostic (Linux, MacOS, Windows...)

Installation

From pypi

Requirements

  • Python 3.7+ with pip
  • nox (pip install nox) in your base Python installation if you want to build the library, docs and run tests from sources
pip install shazzam

Then, if you're not using nox, you'll have to install the various mandatory and optional tools manually:

Cross-Assemblers

At least one of the 2 cross-assemblers should installed.

Packers

IRQ Loaders

From sources

shazzam provides a noxfile to automate the creation of the various virtual environments and install the various tools and docs

git clone https://github.com/shazz/shazzam
cd shazzam
nox -s install
nox -s install_3rd_party
nox -rs docs

Note that you may need to install some OS packages to compile and install the 3rd party tools. Build tools like make, gcc, node, npm, cargo... and archiving tools like unzip, tar...

4 lines example

As shazzam is just a Python library, everything is Python. So even your assembly code looks like Python.

Let's set the C64 border and window color to black:

    label("start")              # define a start label
    lda(imm(0))                 # set accumulator to 0
    sta(at(vic.border_col))     # set border color
    sta(at(vic.bck_col))        # and window color to black

That's it! That's a little more chatty than your traditional assembler but also less prone to error as, as you can see, you have to clearly state if the opcode argument is an address (at), an immediate (imm),...

Features

Python and Assembly

As you can see, this is not some kind of python libraries to generate code, you really write your assembly code, surrounded by any Python code that can interact with the assembly code. Let's try another example, setting the Sprite X and Y coordinates to given values:

    coords = []
    for i in range(80):
        x = int(160+160*(math.sin(i/80*math.pi*2)))
        y = int(100+100*(math.sin(3*i/80*math.pi*2)))
        coords.append((x, y))

    for s in range(8):
        lda(imm(coords[s*10]))
        ldx(imm(coords[s*10]))
        sta(at(vic.sprite0_x+(2*s)))
        sty(at(vic.sprite0_y+(2*s)))

I hope this gave you a basic idea of how Python and the assembly code can mix, the only limit is your imagination :)

Realtime code generation

One of the funny feature of shazzam, that's that in real-time the assembly code is generated and assembled (and crunched, and...). So that means, each time you type any assembly function in Python, you can see the result without executing any python script of whatever except your current code.

A little video is probably better than a lot of words:

[ Insert vscode video here ]

Python-based macros

Like any cross-assembler, you can code in Python generic and reusable snippets to simplify your assembly code. But in this case, this is simple Python function. Here is the 16bits addition macro provided in the library:

def add16(n1, n2, res):
    clc()
    lda(at(n1))
    adc(at(n2))
    sta(at(res)+0)
    lda(at(n1)+1)
    adc(at(n2)+1)
    sta(at(res)+1)

Then in your code, simply import and call it to perform 256+10

import shazzam.macros.macros_math as m

    m.add16(at("var1"), at("var2"), at("result"))

    label("var1")
    byte(0)
    byte(1)
    label("var2")
    byte(10)
    byte(0)
    label("result")
    byte(0)
    byte(0)

    [...]

shazzam provides various sets of ready to use macros to set the VIC banks and memory, some 16bits math operations, to set IRQs, to waste cycles.... Just check shazzam/macros/

Inline testing thru emulation

Inspired from bass, shazzam includes py65emu, a generic 6502 emulator written in Python, it doesn't emulate a C64 or any other hardware than the 6502 CPU. But that's good enough to emulate your routines and check the registers and what is written in the memory.

Practically, in your code, you can add typical assert statements. Here is an example to

    m.add16("var1", "var2", "result")
    brk()

    label("var1")
    byte(0)
    byte(1)
    label("var2")
    byte(10)
    byte(0)
    label("result")
    byte(0)
    byte(0)

    cpu, mmu = s.emulate()
    res = mmu.read(get_current_address()-1)*256 + mmu.read(get_current_address()-2)}
    print(f"Address: ${get_current_address():04X}")
    print(f"Result: {res}")
    assert res == 256

    [...]

And you'll see in your IDE or terminal:

Address: $081B
Result: 266

So this is good news, the macro works :)

And using the built-in 6502 emulator you can do more, check how many cycles were really used between 2 locations in the code, or even step-by-step debugging.

Segments support

The main weakness I found in most 6502 cross-assemblers is the non-existent to minimal support of code segments. At worst you can specify the memory location of the next block (* = $1000 for example), at best some inline segment definition is possible. But fortunately a few cross-assemblers like c64jasm or cc65 have a real great support for relocatable segments and shazzam is using it.

What does it mean? Simply that you can split your code in segment, assemble each one separately and finally link them accordingly by setting the optimal location based on your constraints (VIC banks, memory locations, SID driver...) without tweaking your code, the order of the routines, where sprites should be located...

How does it look like? Extract from the provided hello_world example

with segment(0x0801, assembler.get_code_segment()) as s:

    jsr(at(0x0e544))        # ROM routine to clear the screen Clear screen.Input: – Output: – Used registers: A, X, Y.

    lda(imm(0))
    sta(at(vic.border_col)) # set border color
    sta(at(vic.bck_col))    # and window color to black

    [...]

Within this block, all the code will be starting at address 0x0801, in a segment in this example called CODE (get_code_segment()).

And icing on the cake, shazzam features a Segment Optimizer which automatically finds the best memory arrangement based on the application and C64 constraints.

Crunchers support

Obviously, you can add any cruncher/packer to shrink your data (incbin) or generated PRG but by default, shazzam supports:

  • Exomizer (PRG) (incbin missing)
  • pucrunch (PRG) (incbin missing)
  • nucrunch (PRG) (incbin missing)
  • Alpultra (incbin) (PRG missing)
  • lzsa (PRG and incbin depacker missing)
  • Dyonamite ((PRG and incbin depacker missing))
  • zx7 (incin) (PRG missing)
  • c64f (incbin) (PRG missing)
  • zx0 (todo)

Extract from the crunch_crunch provided example:

prg_cruncher  = Exomizer("third_party/exomizer/exomizer")

def code():
    ...

# finally assemble segments to PRG using cross assembler then crunch it!
assemble_prg(assembler, start_address=0x0801, cruncher=prg_cruncher)

And to crunch a SID file for example:

data_cruncher = Apultra("third_party/apultra/apultra", mode=PackingMode.FORWARD)

def code():
    ...

    with segment(segments["packedata"], "packedata") as s:
        incbin(data_cruncher.crunch_incbin(sidfile))

    with segment(segments["depacker"], "depacker") as s:
        data_cruncher.generate_depacker_routine(s.get_stats().start_address)

    [...]

With each data cruncher, the depacking routine is also provided, just call generate_depacker_routine() as shown in the example.

Packing / depacking performance

The crunch_crunch_[packer] uses a SID file (resources/Meetro.sid) of size 3224 bytes. Here are the performance of each depacker assembly routines:

Agorithm Packed size Slow routine size Slow routine time Fast routine size Fast routine time Faster routine size Faster routine size Size ratio
c64f (zx7) 2268 147 231011 267 166750 70.3%
pyzx7 2269 150 389571 70.3%
lzsa 2 2260 241 239593 252 231471 282 158762 70.1%
lzsa 1 2489 172 195494 306 188114 205 105565 77.2%
Apultra 2163 252 239632 67.1%

IRQ Loaders support

As segments and data can be managed independently, using an IRQ Loader is straight forward. shazzam is able to generate the Sparkle configuration script and run the Sparkle image builder.

Rasterline racer

Racing the beam is probably the traditional hobby of most C64 coders. So to help a little, shazzam can track the instructions timings to be sure your code will fit in the rasterline (including DMA stealing periods, badlines,...).

How does it work? Check this extract from the sprites_galore example:

for y in range(y_scroll, y_scroll+10):
    with rasterline(nb_sprites=8, y_pos=y, y_scroll=y_scroll):
        if (y & 7) == y_scroll:
            nop()
            nop()
            nop()
        else:
            nop()

Python-based C64 files parsers

As this is just Python, up to you to do what you like to do but if it helps, shazzam includes some useful parsers ready to use:

  • SID music player files
  • Koala multicolor pictures
  • SPD v2 sprites files

Just import them!

The i_love_kaoalas example shows how to display a Koala picture in a few lines of code. A little extract:

import shazzam.plugins.plugins as p

def code():

    kla = p.read_kla('resources/panda.kla')

    with segment(0x0801, assembler.get_code_segment()) as s:

        lda(imm(kla.bg_color))      # set border and window color to picture background color
        sta(at(vic.border_col))
        sta(at(vic.bck_col))

    with segment(0xd800, "color_ram", segment_type=SegmentType.REGISTERS) as s:
        incbin(kla.colorram)

    [...]

BeamRacer support

The VLIB and VASYL libraries are ported to shazzam using the shazzam.macros.vlib and shazzam.macros.vasyl packages.

Extract from examples/hello_vasyl:

from shazzam.macros.vasyl import *

with segment(0x00, "VASYL") as s:

    label("dl_start", is_global=True)
    WAIT(48 ,0)

    dl_line_0 = label("dl_line_0")
    MASKV(0)
    WAIT(0, 15)
    MOV(0x20, 0)
    DELAYV(1)
    SKIP()
    WAIT(55 , 59)
    BRA(dl_line_0)
    WAIT(56 ,0)

    [...]

Multi-files application

If your application/demo/game gets big, you can easily split your code by relocatable segments dispatch your segments' code in various files. Simply use the python import statement to include them like in the examples/multi-files example:

@reloading
def code():

    # define here or anywhere, doesn't matter, your variables
    import examples.multi_files.segment_start
    import examples.multi_files.segment_charset

    # generate listing
    gen_code(assembler, gen_listing=True)

    # finally assemble segments to PRG using cross assembler then crunch it!
    assemble_prg(assembler, start_address=0x0801)

    [...]

Simple disassembler

Each time your python code generates some assembly code, the assembly and listing files are generated. But if you want to be sure and check the final generated code, a little 6502 disassembler is provided in tools/.

Usage: python tools/disasm.py -i generated/hello_world/hello_word.prg -o /tmp/hello_word.lst

In case of a prg, the starting address is automatically extracted from the header. Else the -a option can be used to define a specific address.

shazzam assembler directives

As a lot of things can be done directly in Python, shazzam support a minimal set of specific assembler directives:

from shazzam.py64gen import *
  • align(value: int): align the next instruction at a value boundary (will generate call to byte(0) to pad the data)
  • byte(value :int or List[value]: add a byte or a sequence of bytes
  • word(value: int or List[value]: add a word or a sequence of words
  • label(name: str, is_global: bool): define a local or global label at the current address
  • get_anonymous_label(name: str): define an anonymous label
  • incbin(data: bytearray): include a sequence of bytes from an external source (code, file... will generate call to byte())
  • get_current_address(): return current address in the segment
  • get_label_address(label: str): get address for a given label

For each 6502 opcode function (ex lda() or LDA()), the operand type (immediate, address, relative address) has to be specified using the functions:

  • at(value: Any): for an absolute address
  • ind_at(value: Any): for an indirect address
  • rel_at(value: Any): for a relative address
  • imm(value: Any): for an immediate value

and associated 6502 registers:

from shazzam.py64gen import RegisterX as x, RegisterY as y, RegisterACC as a

Notes:

  • if you prefer to use lower case mnemonic, and is replaced by andr to avoid conflict with python operator

Thanks to

All the various open-source projects shazzam is relying on:

  • c64jasm by Nurpax
  • cc65 by cc65 community
  • Doynamite by Bitbreaker
  • Exomizer by Magnus Lind
  • Lzsa by Emmanuel Marty
  • Nucrunch by Christopher Jam
  • Pucrunch by Pasi Ojala
  • Pultra by Emmanuel Marty
  • py65emu by Jeremy Neiman
  • Simple 6502 disassembler by Arthur Ferreira
  • Sparkle by Sparta/OMG
  • zx7 by Einar Saukas and 6502 port by Antonio Villena

And also the beta-testers!

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Not your daddy's C64 cross-assembler...

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c64 cross-assembler 6502

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