Andrew Kesterson
342e4c07da
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docs/ and README.md carry 85 fenced blocks. Every one was checked by hand exactly once, when it was written, which is not a standard that survives a changing interpreter -- and four were already wrong: two transcripts showing a leading space PRINT does not emit, akbasic_TextSink in README.md missing the two members it had grown hours earlier, and FILTER's refusal quoted with wording the code does not use. tests/docs_examples.sh reads a fence-tag vocabulary and runs what it finds. BASIC programs and transcripts run and are byte-compared against an `output` block; C snippets compile with -fsyntax-only against the real include path, which CMake writes out because it is transitive through akerror, akstdlib and akgl; shell blocks run in a sandbox. Anything that would reconfigure the build tree, hit the network or re-enter the suite is tagged norun with the reason in MAINTENANCE.md, and the two cmake blocks stay hand-maintained by decision. An untagged block is a failure rather than a default, and the pass line reports what it executed by kind. Both exist because the way a harness like this dies is by quietly matching nothing and passing -- which it duly did on the first CTest run, where a generator expression evaluating to nothing still contributed an empty argument that the script read as a filename. The count is what caught it. The excerpt check earns its own mention: a block tagged `c excerpt=include/akbasic/sink.h` must still appear in that header, comments and whitespace ignored. Compiling it would only redefine the type, so a compile check could not have found the stale struct, and did not. Registered as the CTest case docs_examples in both configurations. Fixing the four wrong examples turned up two interpreter defects, fixed in the previous commit and recorded in TODO.md section 8. MAINTENANCE.md is new: the fence-tag reference, what to do when the case fails, and the conventions that until now only existed inside source comments -- the three test lists and how two of them invert "passed", the sorted verb table, that a golden file is never edited to suit this interpreter, and that a fix gets mutation-checked with a file copy rather than git checkout. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
100 lines
2.9 KiB
Markdown
100 lines
2.9 KiB
Markdown
# 7. Sound
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The sound verbs need the SDL build and an audio device. Without one they refuse by
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name, and a machine with no sound card still runs the interpreter — only `SOUND` and
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`PLAY` fail, and they say so.
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## SOUND
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```basic requires=akgl
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10 SOUND 1, 4000, 60
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```
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Voice, frequency, duration. Voices are numbered from 1. The duration is in *jiffies* —
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sixtieths of a second — as on a C128, so 60 is one second.
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Further arguments give a frequency sweep: a step, a direction and a range, which is
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what makes a siren or a laser.
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**`SOUND` does not block.** On a C128 the note starts and the program carries on; here
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the same is true, and it has to be — an embedded interpreter that stopped the host's
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frame loop for a second would freeze the game.
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## PLAY
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`PLAY` takes a string of notes:
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```basic requires=akgl
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10 PLAY "C D E F G"
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```
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Within the string:
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|---|---|
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| `A` to `G` | a note |
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| `#` `$` | sharp, flat |
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| `O` *n* | octave |
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| `V` *n* | voice |
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| `T` *n* | envelope preset |
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| `U` *n* | volume |
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| `W`, `H`, `Q`, `I`, `S` | whole, half, quarter, eighth, sixteenth notes |
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| `R` | rest |
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| `.` | dotted |
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Notes are queued and released in time, paced by the host's clock. A program that
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`PLAY`s and then carries on works the way you expect; a program that `PLAY`s and then
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immediately `QUIT`s may not hear all of it.
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`M` — measure — is accepted and does nothing. There is no bar-line accounting to do.
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## TEMPO
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```basic requires=akgl
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10 TEMPO 8
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```
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How fast `PLAY` releases its queue. The number is the same range a C128 uses; the
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constant that turns it into milliseconds is a calibration choice rather than a
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transcription, so it may not match a real machine exactly.
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## ENVELOPE and VOL
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```basic requires=akgl
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10 ENVELOPE 0, 5, 9, 4, 6
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20 VOL 8
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```
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`ENVELOPE` defines one of the ten presets `PLAY`'s `T` selects: attack, decay, sustain
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and release. `VOL` sets the overall volume, 0 to 15.
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## FILTER
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`FILTER` parses and then **refuses at execution**:
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```basic
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10 FILTER 1000, 1, 0, 0, 8
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```
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```output
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? 10 : RUNTIME ERROR FILTER needs a filter stage this device does not have
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```
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It sets the SID's filter cutoff, band switches and resonance. The audio backend
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synthesises raw waveforms and mixes them; there is no filter stage to configure and
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SDL supplies no primitive to build one from. Refusing is deliberate — a program that
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asks for a low-pass and gets an unfiltered square wave has been lied to.
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This is the one verb still waiting on a capability from the graphics library. It is
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filed there rather than worked around here.
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## The clock
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Everything with a duration — `SOUND`, `PLAY`, `TEMPO`, and `SLEEP` from Chapter 2's
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neighbourhood — is paced by a clock the *host* provides. The standalone interpreter
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sets it from a monotonic timer every step, so it just works.
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An embedded host that never sets the clock gets durations that expire immediately:
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audible, but never a hang. That is the intended failure direction.
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