I'm just saying, "yes," it is possible to automate the testing and verification of hardware against a software model.
That's exactly what I'm doing already. User runs automated test. User's simulator fails the test with the result "Reading from $2002 should suppress NMI if read just when it's set ...

DonnaD, your fix would back the PC back up to point to the BRK again, since it subtracts 2 from it. BRK only skips one extra byte, so if you wanted to continue execution just after the BRK opcode, you'd only subtract 1. Even if it were properly subtracting 1, it's still changing the stack pointer ...

This is why I always choose to rely upon automated testing, instead of manual testing, and in particular using test-driven development practices. Manual testing is laborious, error-prone, and a gigantic time-sink in terms of productivity.
Maybe I was unclear. OK, we have a piece of hardware that ...

You are aware that BRK skips the byte after the BRK opcode, right? So this prints 1, not 2 as you might expect:

LDX #0
BRK
INX ; This is skipped
INX
JSR PRINT_X ; Prints 1
...

IRQ:
RTI

I write lots of test programs that are run on hardware and emulators to be sure they both have the same behavior. People often step through them with a debugger in emulators, so I'd like them to be relatively easy to disassemble. I have a few routines that take constant parameters and preserve all ...

My only aim was to catch the error with minimal changes to source, and preferably in a way that doesn't yield one's source incompatible with the standard ca65. I've succeeded in all these respects and have a simple, practical approach, so doubt I'll do much more work on it. Out of curiosity, has ...

Let's see...if you're just marking EQUs whose value is address < 256, to distinguish them from EQU constants < 256, there are at worst only 256 zp address. Some addresses are be defined in terms of others (e.g. PTRH = PTRL+1; that was a really bad example in my previous post).
This is assuming you ...

Having to state that this label is an address, and that label is an address, and this other label is an address, and that other label is an address, and so on seems kinda tedious to me.
I must have utterly failed in my presentation, because for the most part it's automatic. With the second patch ...

The main reason to avoid new syntax, at least right now, is that code will continue to work on the standard ca65 at the very least, with the patched ca65 serving as an optional lint-like assembler.

Not to be picky, but isn't it difficult to be sure that one has never made this error in all 65xx ...

Make this an option that you can turn off
Currently it's --addr-type to turn it on, off by default.

Add an operator to the equate expression for when we explicitly want an address.
Spelled ADDR+ (or +ADDR if you like a suffix). Introducing new syntax makes one's source dependent on the new ...

65xx assemblers differentiate between immediate and address operands by the # character, rather than the instruction's mnemonic:
lda #10 ; A = the number 10
lda 10 ; A = byte at address 10
Since # is not required in other common computer languages or general writing, it is easy to forget. The ...

On the Wiki it is suggested to make code register size-independent by avoiding immediate values and instead referencing them by address. This way if the register is 8 bits, it uses the first byte only, without changing the interpretation of the instructions.
and #$0F ; no, requires that size of ...

Most of my assembly coding is part of reverse-engineering video game consoles, and a common need is to delay N clocks, where N is a constant or run-time value. I figured I'd share the 6502 routines I use, since I found them fun to write. This is the key routine:
; Delays A+20 clocks (excluding JSR ...

Branch instructions that cross a page boundary don't have a penalty cycle.
I may be wrong, but isn't it instead that you don't save a cycle for branches within the same page? That branch takes either 2 clocks (not taken) or 4 clocks (taken)? Perhaps an advantage in simplifying cycle counting, but ...

Here's a pet feature that I'd like to see in a 65xx assembler: typed constants, specifically addresses and numeric constants. These allow an assembler to emit a warning when a numeric constant is used without a # sign, avoiding the obscure error of accidentally using a numeric constant as an address ...