Faintedposts - 269 Mid Summer by Larix

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Points of Interest

• Δ 125. Power Plant
  25 waterwheels are enough. More than enough, actually. - Larix
• Δ 120. Active Program Memory
  Only eight six-bit words are held in memory at a time. Longer programs are spread over multiple code "modules", which are loaded from the ROM bank when needed. With only six bits per command, the instruction set is quite cramped. - Larix
• ¶ 120. Control Panel
  All functions of the computer are run from here: entering code directly, entering information to the main registers, resetting, loading the "boot" program, and of course the big orange lever that starts operation. - Larix
• Δ 120. Instruction Counter
  A plain two-tier counting circuit that advances one position every time an instruction is executed. It has a count capacity of 1260, after which a cart is placed on the pressure plate, disconnecting main power.
  
  If a program just won't finish, termination is forced after 1260 instructions, which means about 420 days (one year three months). This offers a self-contained escape from infinite loops and division through zero, but the effective lack of a halting problem makes the computer conceptually non-turing-complete :P - Larix
• Δ 120. Main data registers
  These three ten-bit registers hold the data the computer operates on. They can be written to or read out, and they can send their data to the adder or the comparator. - Larix
• Δ 120. Primary Decoder
  This simple three-bits-to-eight-paths splitter decodes the first three bits of the current instruction. The resulting signal is either sent to a secondary decoder or in the case of jump instructions directly tries to trigger a jump. - Larix
• Δ 120. Terrible, terrible interface
  The block of hatch covers with several of them open is the "pixel" display. It can display the content of six command words as a pseudo-graphic.
  Most of the circuits are concerned with getting the timing of the computer and its components right. Minecart operation always has delays, and with perpetual-motion carts, those delays are highly variable. - Larix
• Δ 117. Adder
  Using Jong's perfect design - an instant-result ten-bit full adder. Due to various timing concerns, the result is read with a specified delay, by minecarts. It can only add, not subtract, but choosing the inputs properly allows single-instruction data copy from one register to another and a bitwise XOR (useful to generate the binary complement). - Larix
• Δ 117. Comparator and zero-/parity-checker
  To the right, a comparator. It takes one or two inputs, determines if one is larger than the other (or if the only input is larger than zero) and sends one of two possible outputs. I turned this into a direct program flow function - if the condition tested for is not met, the next instruction is skipped.
  
  To the left, a simple identity test - tests whether a counting command results in a zero or in an even number (parity check) and sets the relevant status bit on or off. - Larix
• Δ 117. Program Counter
  A simple minecart ring counter (powered) is at the heart of operations. It advances by one position everytime power is connected to the rollers at the southern wall. Additional machinery has been added so that it can also take care of the two program flow operations "jump" and "skip". - Larix
• Δ 117. Secondary decoders for reading, writing and loading modules
  Paths of minecarts get split by rollers that are powered or not, depending on the input bits' state. Write and Module load choose one of sixteen paths although only three bits of program input are decoded - the final bit is established by an additional (program-manipulable) "status register".
  
  To the left, further powered decoders for the adder, counter, comparator and i/o/status functions are visible. - Larix
• Δ 116. ROM Bank
  Each pair of bridge columns contains sixteen minecarts in perpetual-motion storage. When the "forward" bridge opens, the carts emerge, pass over the reading array, send their data, encoded in weights, to the program memory and then cycle around to enter their pit from the "backward" bridge again. Timing is important. Sixteen modules of eight program words each can be stored, currently there are fourteen. - Larix

Related Maps:

Faintedposts

• 269 Mid Summer [R]

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Map details:

• Fortress Name: Faintedposts
• Map Year: 269 Mid Summer
• Author: Larix
• Submitted by: Larix
• Date Added: 19/01/2015