BenchChapter 9: Special nodes

B71SERVO

The task

P0 reads a knob on CH1. Each frame, P1 sends a pulse, then rests low for 4 ticks of P2.

The pulse lasts 1 plus the reading DIV 20 ticks. P2 ticks every 20 cycles.

Read the knob once, at the start of each frame.

The board

The chip's ports, each with its kind and the parts its signal reaches. Cyan reads, lemon writes. On a narrow screen, scroll the board sideways to see all of it.

Sources: V1 3.5 V, V2 2 V square at 12.5 Hz, and V3 1 V square at 6.25 Hz
Resistors: R1 330 Ω
LEDs: D1 white
Probes: CH1 and CH2

Key idea

A reading of 45 makes a pulse of 3 ticks, and the frame is then 7 ticks long.

Hints

Each hint goes a step further than the one before. Open them one at a time.

Hint 1Show

Count B down from the pulse length; P1 is high while the count is above zero.

Hint 2Show

When the count reaches minus 4, the frame is over: read the knob again.

Solution

Reveal the Full SolutionThe complete program for SERVO. Open it only when you want the answer.

The reference program

The game's own solution. It passes every test and scores exactly par on every benchmark.

A pulse as long as the knob says, then a rest of 4 ticks.

u1SC-2 standard

F: IN P0
DIV 20
ADD 1
L: MOV B, A
JG H
MOV A, 0
H: OUT P1
IN P2
MOV A, B
SUB 1
ADD 4
JZ F
SUB 4
JMP L

CYCLES: 860; at par
ENERGY: 1720; at par
NODES: 1; at par
INSTRUCTIONS: 14; at par

Another way: Two loops

A second program that also passes. It beats par on CYCLES and ENERGY and gives some back on INSTRUCTIONS.

A loop for the pulse, then four sleeps for the rest.

u1SC-2 standard

IN P0
DIV 20
ADD 1
MOV B, A
OUT P1
H: IN P2
MOV A, B
SUB 1
MOV B, A
JNZ H
OUT P1
IN P2
IN P2
IN P2
IN P2

CYCLES: 274; under par
ENERGY: 548; under par
NODES: 1; at par
INSTRUCTIONS: 15; over par