182 lines
5.8 KiB
Typst
182 lines
5.8 KiB
Typst
#import "/lib.typ": example, todo
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= Preventing Interference <timing>
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The protocols as described are very sensitive to the exact timing that the EID counter is
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incremented. The fundamental cause for all types of interference is that we spawn a reference and
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measurement item with too much delay, and some unexpected entity (or entities) spawn in-between. To
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mitigate interference, then, we need that window to be *as short as possible* while still allowing
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us to spawn transmission entities in that window.
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== Tilesets
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The fundamental principle here is to use tile-tick priority (TTP) to set a global order. See
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Charlie's great video on TTP for details. #todo[link video]
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#todo[fix tileset naming. the tileset is the *structure*. the particular sequence is just one instance of that tileset]
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A *tileset* is a sequence of redstone components which all update in the tile tick phase. Components
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later in the sequence have greater significance. To make the significance match our left-to-right
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reading convention, we diagram them so the signal flows right-to-left. For example:
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#todo[screenshot of the same arbitrary tileset]
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```
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cmp 1rep 2rep obs 1rep
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<---------------------
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```
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This section will cover how to read and construct tilesets that enforce a *global* ordering for
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wireless redstone.
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=== The Tile Tick Priority Queue
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The game schedules tile updates through a priority queue; different components have different
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priority, so each stage of the tileset iteratively refines the global order. Across the full
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tileset, we can enforce an arbitrary global ordering.
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#todo[the priority table
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call out here that basic comparators and all other components, so from here on out we're just
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going to use comparators for simplicity.
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]
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Components with different priority always update in priority order, but components with equal
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priority update in scheduled order.
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#todo[rephrase or remove
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The core principal is that repeaters have higher priority than other components. For example, if a
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repeater and comparator are scheduled to activate in the same tick, the repeater always (with one
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exception, if the comparator faces into a diode and the repeater does not) activates before the
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comparator does. By choosing a regular building pattern, we can avoid this exception entirely.
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// Among repeaters, they activate in the order in which they were scheduled. And among
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// comparators, they activate in the order in which they are scheduled. But every repeater
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// activates before any comparator (aside from that one exception). This gives us a *stable sort*
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// which we can use to globally define update order with arbitrary precision.
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]
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#example[
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#todo[this explanation is so janky]
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Say these three tilesets are started in the same gametick, `t=0`.
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```
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<------
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1 rep cmp ab
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2 cmp rep cd
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3 2rep e
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<------
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```
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Once `b`, `d`, and `e` are scheduled, the priority queue looks like this:
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```
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t=2 [d] [b]
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t=4 [e]
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```
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Now at `t=2`, we process the queue in order.
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- `d` activates and schedules `c`.
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- `b` activates and schedules `a`.
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```
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t=4 [e a] [c]
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```
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Now at `t=4`, the end of the tileset, the lanes will always update in order `3 1 2`
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]
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So the full picture involves arbitrary components and priorities. As long as all the tilesets have
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the same total delay and end at the same time, we can determine a global ordering. However the
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general picture is hard to reason about, we basically have to simulate the priority queue to make
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predictions. If we restrict the design of the tilesets a bit, there are two simplifications we could
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take to make things easier to reason about.
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=== Permutation Tilesets
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#todo[describe the mixed delay permutation tilesets and the alphabetization procedure]
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=== Binary
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The simplest tilesets are made entirely of comparators and 2gt repeaters (alternatively: observers
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and 2gt repeaters). Repeaters activate before comparators, so if we think of it like sorting words
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alphabetically, we can identify repeaters with "A" and comparators with "B".
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So, suppose we have a "binary tileset" that is 2gt long. There are two options, A and B. If we
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alphabetize these, we see the A (repeater) always executes before the B (comparator). With such a
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short tileset, that seems trivial; things get more interesting as we add more elements.
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```
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<--
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cmp (B)
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rep (A)
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```
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Now let's use 2 components for a 4gt tileset. There are now four options, AA, AB, BA, BB. We can
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alphabetize these and see the order.
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```
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<------
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cmp cmp (BB)
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cmp rep (BA)
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rep cmp (AB)
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rep rep (AA)
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```
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To break this down: the bottom two (AA, AB) end in repeaters, so they must come first. Among those,
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(AA) comes first. Among the top two (BA, BB), (BA) comes first. It's standard alphabetizing. Just as
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the order of the alphabet creates an ordering over all words, the ordering of the comparator and
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repeater creates an ordering of all tilesets.
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The 6gt tileset. There are now eight options.
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```
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<---------
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...
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```
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As the tilesets get larger, it's less useful to lay out the entire tileset and more useful to find
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the next and previous lanes.
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For example, take this 7-diode tileset.
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```
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cmp rep rep cmp rep cmp cmp
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<--------------------------
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B A A B A B B
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```
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We can easily find the next lane by thinking of this not as a *word* but as a *number*. We have two
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options, and one is greater than the other.
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```
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cmp rep rep cmp rep cmp cmp
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<--------------------------
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B A A B A B B
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1 0 0 1 0 1 1
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```
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We can think of this tileset as a 7-bit binary number, in this case the value 75. We can find the
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next lane by simply incrementing by one.
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```
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1 0 0 1 0 1 1 (75)
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+ 1
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1 0 0 1 1 0 0 (76)
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<--------------------------
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cmp rep rep cmp cmp rep rep
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```
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=== Lexicographic
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=== Jamming
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== Block Event Delay
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== Single-Priority Loops
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