What is M2?

[Zepper]

I verified that by leaving M2 low while writing to the mapper

What is M2?

[infiniteneslives]

Aka phi2, CPU clock.

[Zepper]

Aka phi2, CPU clock.

Odd and even clocks?

[infiniteneslives]

Aka phi2, CPU clock.

Odd and even clocks?

Yeah, every CPU cycle. Falling edges of M2/phi2 defines the end of one cycle and beginning of the next.

The mmc1 basically keeps track of what the last cycle was, if it was a write cycle, then it doesnt allow writes to the shift register. It only allows writes if the last cycle was a read cycle. That's why the garbage writes of RMW instructions is the one that gets latched, and the actual write that follows is ignored.

[Zepper]

It should be "odd then even cycles", or xx1->xx0, correct?

[infiniteneslives]

It should be "odd then even cycles", or xx1->xx0, correct?

I'm not 100% sure what you're saying...

It's EVERY CPU cycle. Not sure how to be more clear than that.

I really don't know what an odd vs even CPU cycle is... Are you defining odd vs even based on the program counter (PC) being odd/even? If so, my answer is still no. I think it's safe to say mappers never know if it's an even/odd CPU cycle.

Perhaps the even/odd confusion is coming from the '2' in M2 (aka phi2). The '2' doesn't mean even. '2' is just a label. phi1 is some other clock that I can't recall off hand.

[lidnariq]

φ1 and φ2 are active-high signals that denote the "internal processing half" and "external bus half" of 6502 activity. They're the logical inversion of each other. No even/odd to it, though.

[ulfalizer]

Each cycle has a φ1 and a φ2, of equal length. The φ1 half-cycle occurs while the input clock is low, the φ2 half-cycle while it is high. They do not span a full cycle, if that's where you got even/odd from.

http://wiki.nesdev.com/w/index.php/CPU_ ... escription was updated recently and covers it too.

[koitsu]

http://wiki.nesdev.com/w/index.php/CPU_ ... escription was updated recently and covers it too.

If you're referring to my recent 2 updates: those were in response to the bottom half of this blog post (FYI: Japanese, and Google Translate is not sufficient here). Basically the post consists of a very intelligent guy (see his blog; he does all kinds of hardware work on Famicom stuff) questioning the pinout being called M2 rather than φ2/phi2, and noted that someone's excessive OCD with fraction symbols in fonts made it very hard for him to read the text clearly (apparently some Japanese computers/setups print gobbledegook for those glyphs). But by the end of the post answers his own question (sort of; he concludes that someone likely called it M2 because of familiarity with the Z80 CPU's "M1" pin (not functionality, but the naming convention)). He had other complaints as well -- I had to get my neighbour (who does professional Jap/Eng translation for Nikon) to help me understand what all was being said. My edit was done to clean all this up and more; refer to the diff.

If you were referring to older updates, then ignore what I said above. :-)

[tepples]

But by the end of the post answers his own question (sort of; he concludes that someone likely called it M2 because of familiarity with the Z80 CPU's "M1" pin (not functionality, but the naming convention)).

I was under the impression that M stood for "modified". If there is a connection to the Z80, I wonder how to phrase that most clearly.

[lidnariq]

I'd arbitrarily guess that the M in M2 stands for "memory".

I really doubt it has anything in common with Z80 parlance, where there are a family of different memory access timings (M1 through M5, at least) corresponding to different parts of instruction execution.

[Zepper]

Technical terminology isn't friendly for reading. So, I'd like to suggest what Disch did with his texts - something readable by everyone.

[lidnariq]

Without telling us what specific thing you're confused by, it's very difficult to make it clearer.

I'm not even clear where you got "Odd and even clocks" from.

[ulfalizer]

http://wiki.nesdev.com/w/index.php/CPU_ ... escription was updated recently and covers it too.

If you're referring to my recent 2 updates: those were in response to the bottom half of this blog post (FYI: Japanese, and Google Translate is not sufficient here). Basically the post consists of a very intelligent guy (see his blog; he does all kinds of hardware work on Famicom stuff) questioning the pinout being called M2 rather than φ2/phi2, and noted that someone's excessive OCD with fraction symbols in fonts made it very hard for him to read the text clearly (apparently some Japanese computers/setups print gobbledegook for those glyphs). But by the end of the post answers his own question (sort of; he concludes that someone likely called it M2 because of familiarity with the Z80 CPU's "M1" pin (not functionality, but the naming convention)). He had other complaints as well -- I had to get my neighbour (who does professional Jap/Eng translation for Nikon) to help me understand what all was being said. My edit was done to clean all this up and more; refer to the diff.

If you were referring to older updates, then ignore what I said above.

I remember clarifying φ1/2 recently, but might be misremembering. Maybe it was in the Visual Circuit Tutorial.

[ulfalizer]

If you're counting in half-cycles, φ1 would be even half-cycles and φ2 odd half-cycles. That seems like a weird way to think about it though. φ1 is just the first part of the CPU cycle and φ2 the second.