viewtopic.php?f=2&t=7500

I do.

If you run some code, you'll see the emulator works fine. The internal values of the registers are OK, but the visualization is wrong. I tried some creative ways to fix it by reverse engineering the software, but it way beyond my capabilities.

I am seeing something so obvious, that nobody else is pointing out, that I am completely sure i am 100% wrong but....

Doesn't that first instruction. BRA init. mean that all the LDA are never executed? You don't mention where the code starts but I am assuming, it starts at init.

You mention your ...

Hi!

I like the stacked design. I went for it with my 74HCT6526 , but the connector I used were very flimsy and unreliable. That gave me a ton of headaches.

I am planning to restart the project soon, and I think the PC104 form factor is a good choice. Could you point me to the connectors and the ...

Definitely... this took way longer than expected, but...

lab.jpeg

We've finally got our new home, after almost a two-year delay! This room will eventually be my workshop. Yay!

We still have (at least) a couple of months before we move in, but things are looking good now.

I hope to share more ...

“Current PC” meaning what? The offset is computed relative to the address of the next instruction, not the value of PC at the PER opcode. Assuming the instruction is PER $1234 and is assembled at $AB0000 , the base address from which the offset will be computed will be $AB0003 and the offset will ...

So...

PEA will be
PEA #$1234

Which assembles to F4 34 12. On execution, $12 is pushed into the stack, then $34.

PEI will be
PEI $20

The following code :


LDA #$12
STA $21
LDA #$34
STA $20
PEI

With DP=0x0000, M=1 (M=1, to have 8bit loads into the Accumator, PEI is not affected by M ...

If the opcode targets the Accumulator, then the operand size depends only on the M flag. If the opcode targets X or Y, then it only depends on the X flag. It makes sense to me, but still...
That is correct if an immediate-mode instruction is being disassembled.

Awesome, thanks for the feedback ...

And now, a complete disassembler! The original project had a 6502 disassembler, which I have extended to work with all 65816 opcodes and addressing modes.

When using immediate addresing, to choose between an 8bit or 16bit operand, the current M and X flags are taken into account. Also, the ...

It may not be much but.... I now have a second opcode implemented!

Ok. No, it is not much to be honest... but I've been doing more things meanwhile.

The new opcode is XCE and with it, the ability to switch between native and emulation modes. The status register properly reacts to this, swapping ...

If you want a 100 percent, accurate emulation, you need a real 65C816 on which to experiment. :D

Absolutely no tinkering with any real hardware (beyond my laptop) is allowed while the whole family is stuck in a 35 square meter (aprox 375 sq feet) apartment :lol: :lol: :lol:

At least, it is ...

So there are rules, but they have exceptions, but they too have exceptions, but they...

It's time to get a real, 100% accurate emulator, so I can test every opcode, one step at a time.

Thank you for all those insights!

For example, if the accumulator is set to 8 bits, the index registers are set to 16 bits and TXA is executed, where does the MSB in the X-register go?

That could have been an interview question for some 65816 programmers position back in the 90s! With my current understanding... I'd say X's MSB ...

Next milestone, decoding and implementing all instructions related to mode switching (Native vs Emulation, 8 vs 16 bit registers)
The 816 has two operating modes: emulation and native. Changing register width whilst operating in native mode isn’t “mode switching,” as instruction behavior in itself ...

Two little achievements to add to the list.

A proper fetch/decode loop is now implemented into the emulation. On decode cycle 0, the opcode is fetched into the IR. From there on, a function is called using a function array based on the opcode. Each opcode function advances the decode cycle counter ...

Splendid - I do like a logic analyser view.

If you haven't already found it, Bruce's document on the '816 details all known behaviours and quirks, I think.
http://6502.org/tutorials/65c816opcodes.html

Yep, I've got that one. It is an splendid document! I have quite a long list of documents to ...