Questions & Clarifications regarding APU Sweep

Links:
APU Sweep page - https://www.nesdev.org/wiki/APU_Sweep
Barrel shifter "page" - https://www.nesdev.org/wiki/Visual_circ ... l_shifters
Barrel shifter Wikipedia - https://en.wikipedia.org/wiki/Barrel_shifter
Bit shift Wikipedia - https://en.wikipedia.org/wiki/Bitwise_o ... Bit_shifts


A project I'm working on has me implementing the APU. When I got to the Sweep, the wiki article stumped me for a bit. While most of my confusion was solved by just reading more carefully, the barrel shifter was never really clear. In trying to clarify it, I ended up raising more questions. Here are those questions and concerns:

• The Sweep page does not link to either the barrel shifter page or Wikipedia article when it could/should.

• The barrel shifter page and a Google search will bring you to the Wikipedia page, which, at a quick look, suggests a bit rotation operation. My testing and other implementations I've seen reveal a logical shift operation (at least in the Sweep). This is not specified on either the Sweep or barrel shifter page.

• The Sweep page says that the negation happens after the shift; the barrel shifter page says the negation happens first. This seems to be an inconsistency and (I believe) will result in slightly different logic.

• One of the discussion posts on the Sweep page explains the physical difference between the two channels. This may not matter logic-wise, but clarifying where these differing lines go could be important.

Statistics: Posted by Trainmaster2 — Wed Feb 14, 2024 2:03 pm — Replies 0 — Views 38

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