Get Started with 6502 Assembly Programming on Atari Lynx

https://atarigamer.com/articles/get-started-with-6502-assembly-programming-on-atari-lynx

by ikromin • 7 years ago

77 38 7 years ago

vga805• 7 years ago

I understand the font choice, but you might want to reconsider. It's not easy to read.

nategri3• 7 years ago

Learning to write 6502 was a formative experience for me as a programmer and I strongly recommend it as a pedagogical exercise if nothing else. The instruction set is tiny, and easy to grapple with, but after learning it you'll get an intuitive grasp of, for instance, "why the C programming language is the way it is."

So all that remains is to pick a platform! And there's no shortage of them. Glad to see Lynx is yet another participant in the vibrant 6502 homebrew community.

tellak• 7 years ago

why the C programming language is the way it is.

I’m curious specifically why you think this is. The 6502 with its poor register set and special purpose addressing mode seems to make it a relatively terrible/challenging C target.

danmaz742• 7 years ago

Not OP, but I learned assembly on the 6502, and its simplicity make it easy to create a mental model of the internals of a CPU - these relate very well with a low level language like c, even if today's CPUs are so much more advanced (and difficult to study).

verisimilitudes• 7 years ago

The instruction set is tiny, and easy to grapple with, but after learning it you'll get an intuitive grasp of, for instance, "why the C programming language is the way it is."

If you want that, you should learn the PDP-11 instruction set, which is actually why the C language is the way it is. In particular, C is rather uniquely unsuited for segmented memory models, which many 6502 systems have, whereas other languages with lower-level features or accommodations can easily function under such a memory model, because they were designed with it in mind instead of solely for the PDP-11.

On that note, C isn't actually a low-level language and I'm aware the 6502 is an example of an instruction set it maps very poorly to, compared to how a machine code programmer would approach it, so I'm curious why you made this relationship, since it's rather tenuous.

nategri3• 7 years ago

Feel free to abstract it to "how programming languages interface with memory."

duskwuff4• 7 years ago

In particular, C is rather uniquely unsuited for segmented memory models

C was often used to program 16-bit x86 systems, and it handled that well enough.

A more relevant limitation of the 6502, however, is its stack. The 6502 stack is limited to a single page of 256 bytes, and there is no stack-relative addressing mode. This makes a C-style stack difficult to implement -- most C implementations for the 6502 implement a secondary data stack in main memory.

kgwxd2• 7 years ago

Atari 2600 programming is 6502 too, you can play with it right in the browser: http://8bitworkshop.com/v3.3.0/?=&file=examples%2Fcomplexsce...

tom_• 7 years ago

My suggestion: anybody thinking of getting started with 6502 will probably have more fun with the Atari Lynx.

Malic• 7 years ago

Or the C64 might be a good choice too.

Jumping into "no-framebuffer/racing-the-beam" 6502 programming on the Atari 2600 for the uninitiated is just ... cruel.

LIV2• 7 years ago

Nice!

Another good resource is forum.6502.org as there are plenty of 6502 experts there that have built their own 6502 machines for a hobby

tenebrisalietum• 7 years ago

Including one made out of discrete components. https://monster6502.com/

jcmeyrignac2• 7 years ago

There is a typo in the chapter "Important commands that don't exist!".

NEG is described as:

  EOR #255 (XOR/Flip bits)
  SEC (Clear carry)
  ADD #1  (add 1)

Of course, it's:

  EOR #255 (XOR/Flip bits)
  CLC (Clear carry)
  ADC #1  (add 1 with carry 0)

or:

  EOR #255 (XOR/Flip bits)
  SEC (Set carry)
  ADC #0  (add 0 with carry 1)

jcmeyrignac2• 7 years ago

Another one: DEC (dec de)

   INC z_E
   BNE    IncDE_Done
   INC    z_D
  IncDE_Done:

Should be:

   LDA z_E
   BNE DecDE
   DEC z_D
  DecDe:
   DEC z_E

jdswain• 7 years ago

There is an INC A instruction on the 65C02 and 65816, so this is better if you have anything newer than the NMOS 6502:

  EOR #255   ; Invert
  INC A      ; Add 1

It looks like the Lynx has a 65SC02 which is a 65C02 without the bit manipulation instructions, so it should have the INC A instruction.

zellyn2• 7 years ago

Here's an in-browser 6502 tutorial with simulator: https://skilldrick.github.io/easy6502/

Of course, you can pick the system/context you want to learn in: many 8-bit computers used 6502 chips. For example, this book is well-regarded for those with Apple II nostalgia: https://archive.org/details/AssemblyLinesCompleteWagner

I'm sure there are tons of NES-targeted tutorials too.

dillonmckay• 7 years ago

Anybody have good NES tutorials and also a link for a way to put it on a cart (sd or whatever)?

Also, are their free or paid-for asset libraries?

Thanks in advance!

zellyn2• 7 years ago

Googling [nes 6502 tutorial] pulled up a good selection of articles.

nwallin• 7 years ago

nesdev.com is a treasure trove of information.

To put it on a cart, you'll use RetroUSB PowerPak or Everdrive N8.

Don't know about assets.

rbanffy4• 7 years ago

I wonder why people say it's a 16-bit console if it's based on the 65SC02. The 65816 and 802 were 16 bit, but the SC02, AFAIK, was not.

ArnoVW• 7 years ago

The 6502 could perform 8-bit operations, but had a 16-bit address space. Hence the C64 (= 2^16)

rbanffy4• 7 years ago

By that reasoning, the Apple II is a 16-bit computer and the original Mac a 24-bit one.

glhaynes• 7 years ago

It had a 16-bit graphics processor, which arguably was a lot more important for its software than whether the CPU was 16-bit.

See also the TurboGrafx-16 console, which had a similar arrangement: an 8-bit 6502-descendent and a 16-bit graphics chip. It got a lot of flak for being “fake 16-bit”. I think the Lynx was better able to get away with it because it was on such a different level than other handhelds of the time (besides maybe the expensive portable version of the TG-16!), whereas the TG-16 had to go up against the 68000-based Sega Genesis.

rbanffy4• 7 years ago

So I guess I'll say my Chromebook has 2 + 160 + 20 + 2 or about 184 cores. I'm counting the integrated GPU, of course.

FPGAhacker• 7 years ago

Wow. I bought a Lynx with my first paycheck from my first “real” job when I was 15. I played California Games a lot.

burfog3• 7 years ago

The closest modern equivalent to those old 8-bit computers is the TI-84 Plus CE calculator. It has a legit (no hacks) way to load binary executables. It goes for about $100. Like many old 8-bit computers, it comes with BASIC and an almost-ASCII character set. The screen is 320x240, just a tad bigger than those old 8-bit home computers usually had, though with 16-bit color. There is a USB port. You get a bit more RAM, with about 64 KiB of about 256 KiB available for your program. The screen is at a fixed address you can write to.

The C compiler is fascinating. There is a uint24_t which maps to an unsigned int. This is because the EZ80 CPU is capable of ganging three 8-bit registers together to handle 24-bit data. Pointers are also 24-bit. The "short" and "long" types are of normal size, 16-bit and 32-bit. There is no alignment or padding. Serious stuff needs to be in assembly. The C compiler doesn't optimize very well.

So that is 3 programming languages on a $100 device that happens to be useful for all sorts of normal school classes. The calculator is fine for the SAT, ACT, AP Statistics, AP Calculus, and now even the AP sciences.

aidenn0• 7 years ago

I remember having a printout of the tasm tables for x80 so I could type hex machine-code into my TI-83 (it could load hex programs as binaries). I don't recommend that approach, but I certainly learned a lot.

Get Started with 6502 Assembly Programming on Atari Lynx

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