NES Emulator Part #2: The CPU (6502 Implementation)

In this video I build a 6502 emulation in C++. I pay close attention to the instructions that can cause problems, ADC and SBC. Then I build a lightweight application to analyze running 6502 programs.

[vspecky]

Can we just take a moment and appreciate the fact that this guy didn't put a single ad on an hour long video?

[waseinmalwar]

1 hour of David speaking about opcodes? Is this heaven?

[LS_NE]

Life goals, having a wife that can double check my opcodes

[remique]

Dude, your content is pure gold. I love the fact that you thoroughly explain every concept and not only show the code, while still being concise.

[code-dredd]

Chemists have The Periodic Table of Elements.
We Software Engineers have The Mnemonic Table of Opcodes.

[victornpb]

I’m on YouTube since 2005, I never been so excited to see a part 2 video in my entire life!

[SolusPrimus]

You are the personification for actual, usefull qualitycontent about c++. Be proud!

[InfiniteQuest]

Wow, you have a very patient and understanding wife.

[zlatkovnik]

Why are you much more interesting than my college professor when talking about the same subject? Good work!

[VirtuelleWeltenMitKhan]

The test ROMs are a super nice thing to have.
A wife which is willing to check your code is even better.

[code-dredd]

@53:43:

This is an attempt to clarify a potential point of confusion for others who may not be too familiar with the stack. Normally, the stack pointer (i.e. `stkp`) should be pointing to the element at the top of the stack. However, in the code as shown, the `stkp` isn't really pointing directly to the top element. Rather, it's pointing to the (logically) "empty" location where the next element should go when pushed, which is why the `write(0x0100 + stkp, a)` call is made first in `PHA` before decrementing the pointer with `stkp--`. Consistent with this, in `PLA`, you can see that the `stkp` is first incremented before reading, so that it moves from the (logically) "empty" stack position down to the actual top element in the stack.

I mention this because "normally", you'd expect the `stkp` to be pointing to the top element directly at all times, which would mean that on push, you'd be `stkp--` and then `write(...)`, and on pop you'd be doing `read(...)` and then `stkp++`, in that order.

BTW, if you're wondering why `stkp` is decremented in value when the stack itself is supposed to be growing in size (and vice-versa), the reason is that stacks grow from high memory addresses down to lower memory addresses.

GG

[lallenlowe]

Oh man, this series is coming at the best time. I love you. May I recommend Ben Eater's 8 bit computer on bread boards series for anyone wanting to understand the electrical underpinnings of a CPU.

[wllngtnds]

YES! I was looking forward to second part of this new series.

[Simple_Simon_UK]

I can't stop giggling. You have taken me right back in time.
I wrote a 6800 Emulator (Dissassembler) in Pascal, during my second year at University in 1984!
The Ureka moment for this most daunting of tasks was when I devised the table of Instructions and Addressing Modes. Once I'd created the table, the implementation of the CPU was a doddle.
I love the elegance of your C++.
You are a very clever cookie.

[vtomasr]

I think I'm more exited about the well organized and educational content rather than the NES emulator itself ;)

[saraweber]

This is honestly amazing! This is basically a college course that's free. Keep up the good work man!

[amisnerk]

You did your whole presentation, outside, in the heat and didn't take one sip of your soda.




You absolute legend. XD

[StuBonham]

Incredible stuff - I programmed 6502 back in the day, and this brought back a lot of memories.

[Heisenberg]

Fills so many gaps I never cared about to fill back in the days though it was all in front of me... had to care about so many other things. Great video.

[WagnerSchmitt]

Since your first video I already started building my own Emulator. You were right, it is such a wonderful project to work on.
It was something I also wanted to do a long time ago, and your videos gave me the motivation to start.
Thank you for that, and for making the videos so didactic.