Added some prereqs

README.org

@@ -0,0 +1,6 @@
+This is the chisel intro for the TDT4255 course at NTNU.
+If you use it for your cours, please let me know how it went and feel 
+free (or even slightly pressured) to submit pull requests with improvements.
+
+TODO: Installation instructions, link to scala primer and link to other tutorials.
+Also lacking images, they're on the way.

oppgavetekst.org

@@ -6,8 +6,30 @@
   
 * Chisel
 ** Prerequisites
-   You should have some idea of how digital logic circuits work.
-  
+   + You should have some idea of how digital logic circuits work.
+     Do you know what a NAND gate is? 
+     Do you know how many wires you need to address 64kb of memory? 
+     If so you should be able to pick it up :)
+   + You must be able to run scala programs. 
+     If you can run java then you can run scala.
+     If not grab the jvm. Remember to curse Larry Page if you pick it up from the
+     oracle webpage.
+   + Some flavor of GNU/Linux, or at least something UNIX-like.
+     If you use anything other than Ubuntu 16.04 or 18.04 I won't be able to offer
+     help if something goes wrong.
+   + An editor suited for scala.
+     My personal recommendation is GNU Emacs with emacs-lsp for IDE features along
+     with the metals language server (which works for any editor with lsp (language 
+     server protocol), such as vim, vscode and atom).
+     If you prefer an IDE I hear good things about intelliJ, however I haven't tested
+     it personally, so if odd stuff happens I can't help you.
+   + Optional: sbt
+     You can install the scala build tool on your system, but for convenience I've
+     included a bootstrap script in sbt.sh.
+     sbt will select the correct version for you, so you don't have to worry about
+     getting the wrong version.
+
+
 ** Terms
    Before delving into code it's necessary to define some terms.
    
@@ -108,10 +130,19 @@
    }
    #+end_src
    
+   What about running it?
+
+   In chisel the only reason to run a program is to produce a schematic that can be uploaded to an
+   FPGA (or plugged into an ASIC manufacturing toolchain)
+   
+   Instead of synthesizing our design and running it on FPGAs we will instead rely on software emulator
+   testing, thus all your code will be run via the supplied test harness.
+
 ** Scala and chisel
-   The code for these snippets can be found in Example.scala in the test directory.
+   The code for the snippets in this subchapter can be found in Example.scala in the test directory.
    You can run them using sbt by running ./sbt in your project root which will open
    your sbt console.
+   This will start a large download, so be patient even if it looks like it's stuck.
  
    A major stumbling block for learning chisel is understanding the difference between scala and chisel.
    To highlight the difference between the two consider how HTML is generated.

sbt.sh

@@ -0,0 +1,569 @@
+#!/usr/bin/env bash
+#
+# A more capable sbt runner, coincidentally also called sbt.
+# Author: Paul Phillips <paulp@improving.org>
+# https://github.com/paulp/sbt-extras
+
+set -o pipefail
+
+declare -r sbt_release_version="1.2.8"
+declare -r sbt_unreleased_version="1.2.8"
+
+declare -r latest_213="2.13.0-RC1"
+declare -r latest_212="2.12.8"
+declare -r latest_211="2.11.12"
+declare -r latest_210="2.10.7"
+declare -r latest_29="2.9.3"
+declare -r latest_28="2.8.2"
+
+declare -r buildProps="project/build.properties"
+
+declare -r sbt_launch_ivy_release_repo="http://repo.typesafe.com/typesafe/ivy-releases"
+declare -r sbt_launch_ivy_snapshot_repo="https://repo.scala-sbt.org/scalasbt/ivy-snapshots"
+declare -r sbt_launch_mvn_release_repo="http://repo.scala-sbt.org/scalasbt/maven-releases"
+declare -r sbt_launch_mvn_snapshot_repo="http://repo.scala-sbt.org/scalasbt/maven-snapshots"
+
+declare -r default_jvm_opts_common="-Xms512m -Xss2m"
+declare -r noshare_opts="-Dsbt.global.base=project/.sbtboot -Dsbt.boot.directory=project/.boot -Dsbt.ivy.home=project/.ivy"
+
+declare sbt_jar sbt_dir sbt_create sbt_version sbt_script sbt_new
+declare sbt_explicit_version
+declare verbose noshare batch trace_level
+declare debugUs
+
+declare java_cmd="java"
+declare sbt_launch_dir="$HOME/.sbt/launchers"
+declare sbt_launch_repo
+
+# pull -J and -D options to give to java.
+declare -a java_args scalac_args sbt_commands residual_args
+
+# args to jvm/sbt via files or environment variables
+declare -a extra_jvm_opts extra_sbt_opts
+
+echoerr () { echo >&2 "$@"; }
+vlog ()    { [[ -n "$verbose" ]] && echoerr "$@"; }
+die ()     { echo "Aborting: $*" ; exit 1; }
+
+setTrapExit () {
+  # save stty and trap exit, to ensure echo is re-enabled if we are interrupted.
+  SBT_STTY="$(stty -g 2>/dev/null)"
+  export SBT_STTY
+
+  # restore stty settings (echo in particular)
+  onSbtRunnerExit() {
+    [ -t 0 ] || return
+    vlog ""
+    vlog "restoring stty: $SBT_STTY"
+    stty "$SBT_STTY"
+  }
+
+  vlog "saving stty: $SBT_STTY"
+  trap onSbtRunnerExit EXIT
+}
+
+# this seems to cover the bases on OSX, and someone will
+# have to tell me about the others.
+get_script_path () {
+  local path="$1"
+  [[ -L "$path" ]] || { echo "$path" ; return; }
+
+  local -r target="$(readlink "$path")"
+  if [[ "${target:0:1}" == "/" ]]; then
+    echo "$target"
+  else
+    echo "${path%/*}/$target"
+  fi
+}
+
+script_path="$(get_script_path "${BASH_SOURCE[0]}")"
+declare -r script_path
+script_name="${script_path##*/}"
+declare -r script_name
+
+init_default_option_file () {
+  local overriding_var="${!1}"
+  local default_file="$2"
+  if [[ ! -r "$default_file" && "$overriding_var" =~ ^@(.*)$ ]]; then
+    local envvar_file="${BASH_REMATCH[1]}"
+    if [[ -r "$envvar_file" ]]; then
+      default_file="$envvar_file"
+    fi
+  fi
+  echo "$default_file"
+}
+
+sbt_opts_file="$(init_default_option_file SBT_OPTS .sbtopts)"
+jvm_opts_file="$(init_default_option_file JVM_OPTS .jvmopts)"
+
+build_props_sbt () {
+  [[ -r "$buildProps" ]] && \
+    grep '^sbt\.version' "$buildProps" | tr '=\r' ' ' | awk '{ print $2; }'
+}
+
+set_sbt_version () {
+  sbt_version="${sbt_explicit_version:-$(build_props_sbt)}"
+  [[ -n "$sbt_version" ]] || sbt_version=$sbt_release_version
+  export sbt_version
+}
+
+url_base () {
+  local version="$1"
+
+  case "$version" in
+        0.7.*) echo "http://simple-build-tool.googlecode.com" ;;
+      0.10.* ) echo "$sbt_launch_ivy_release_repo" ;;
+    0.11.[12]) echo "$sbt_launch_ivy_release_repo" ;;
+    0.*-[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]-[0-9][0-9][0-9][0-9][0-9][0-9]) # ie "*-yyyymmdd-hhMMss"
+               echo "$sbt_launch_ivy_snapshot_repo" ;;
+          0.*) echo "$sbt_launch_ivy_release_repo" ;;
+    *-[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]-[0-9][0-9][0-9][0-9][0-9][0-9]) # ie "*-yyyymmdd-hhMMss"
+               echo "$sbt_launch_mvn_snapshot_repo" ;;
+            *) echo "$sbt_launch_mvn_release_repo" ;;
+  esac
+}
+
+make_url () {
+  local version="$1"
+
+  local base="${sbt_launch_repo:-$(url_base "$version")}"
+
+  case "$version" in
+        0.7.*) echo "$base/files/sbt-launch-0.7.7.jar" ;;
+      0.10.* ) echo "$base/org.scala-tools.sbt/sbt-launch/$version/sbt-launch.jar" ;;
+    0.11.[12]) echo "$base/org.scala-tools.sbt/sbt-launch/$version/sbt-launch.jar" ;;
+          0.*) echo "$base/org.scala-sbt/sbt-launch/$version/sbt-launch.jar" ;;
+            *) echo "$base/org/scala-sbt/sbt-launch/$version/sbt-launch.jar" ;;
+  esac
+}
+
+addJava ()     { vlog "[addJava] arg = '$1'"   ;     java_args+=("$1"); }
+addSbt ()      { vlog "[addSbt] arg = '$1'"    ;  sbt_commands+=("$1"); }
+addScalac ()   { vlog "[addScalac] arg = '$1'" ;   scalac_args+=("$1"); }
+addResidual () { vlog "[residual] arg = '$1'"  ; residual_args+=("$1"); }
+
+addResolver () { addSbt "set resolvers += $1"; }
+addDebugger () { addJava "-Xdebug" ; addJava "-Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=$1"; }
+setThisBuild () {
+  vlog "[addBuild] args = '$*'"
+  local key="$1" && shift
+  addSbt "set $key in ThisBuild := $*"
+}
+setScalaVersion () {
+  [[ "$1" == *"-SNAPSHOT" ]] && addResolver 'Resolver.sonatypeRepo("snapshots")'
+  addSbt "++ $1"
+}
+setJavaHome () {
+  java_cmd="$1/bin/java"
+  setThisBuild javaHome "_root_.scala.Some(file(\"$1\"))"
+  export JAVA_HOME="$1"
+  export JDK_HOME="$1"
+  export PATH="$JAVA_HOME/bin:$PATH"
+}
+
+getJavaVersion() {
+  local -r str=$("$1" -version 2>&1 | grep -E -e '(java|openjdk) version' | awk '{ print $3 }' | tr -d '"')
+
+  # java -version on java8 says 1.8.x
+  # but on 9 and 10 it's 9.x.y and 10.x.y.
+  if [[ "$str" =~ ^1\.([0-9]+)\..*$ ]]; then
+    echo "${BASH_REMATCH[1]}"
+  elif [[ "$str" =~ ^([0-9]+)\..*$ ]]; then
+    echo "${BASH_REMATCH[1]}"
+  elif [[ -n "$str" ]]; then
+    echoerr "Can't parse java version from: $str"
+  fi
+}
+
+checkJava() {
+  # Warn if there is a Java version mismatch between PATH and JAVA_HOME/JDK_HOME
+
+  [[ -n "$JAVA_HOME" && -e "$JAVA_HOME/bin/java"     ]] && java="$JAVA_HOME/bin/java"
+  [[ -n "$JDK_HOME"  && -e "$JDK_HOME/lib/tools.jar" ]] && java="$JDK_HOME/bin/java"
+
+  if [[ -n "$java" ]]; then
+    pathJavaVersion=$(getJavaVersion java)
+    homeJavaVersion=$(getJavaVersion "$java")
+    if [[ "$pathJavaVersion" != "$homeJavaVersion" ]]; then
+      echoerr "Warning: Java version mismatch between PATH and JAVA_HOME/JDK_HOME, sbt will use the one in PATH"
+      echoerr "  Either: fix your PATH, remove JAVA_HOME/JDK_HOME or use -java-home"
+      echoerr "  java version from PATH:               $pathJavaVersion"
+      echoerr "  java version from JAVA_HOME/JDK_HOME: $homeJavaVersion"
+    fi
+  fi
+}
+
+java_version () {
+  local -r version=$(getJavaVersion "$java_cmd")
+  vlog "Detected Java version: $version"
+  echo "$version"
+}
+
+# MaxPermSize critical on pre-8 JVMs but incurs noisy warning on 8+
+default_jvm_opts () {
+  local -r v="$(java_version)"
+  if [[ $v -ge 8 ]]; then
+    echo "$default_jvm_opts_common"
+  else
+    echo "-XX:MaxPermSize=384m $default_jvm_opts_common"
+  fi
+}
+
+build_props_scala () {
+  if [[ -r "$buildProps" ]]; then
+    versionLine="$(grep '^build.scala.versions' "$buildProps")"
+    versionString="${versionLine##build.scala.versions=}"
+    echo "${versionString%% .*}"
+  fi
+}
+
+execRunner () {
+  # print the arguments one to a line, quoting any containing spaces
+  vlog "# Executing command line:" && {
+    for arg; do
+      if [[ -n "$arg" ]]; then
+        if printf "%s\n" "$arg" | grep -q ' '; then
+          printf >&2 "\"%s\"\n" "$arg"
+        else
+          printf >&2 "%s\n" "$arg"
+        fi
+      fi
+    done
+    vlog ""
+  }
+
+  setTrapExit
+
+  if [[ -n "$batch" ]]; then
+    "$@" < /dev/null
+  else
+    "$@"
+  fi
+}
+
+jar_url ()  { make_url "$1"; }
+
+is_cygwin () { [[ "$(uname -a)" == "CYGWIN"* ]]; }
+
+jar_file () {
+  is_cygwin \
+  && cygpath -w "$sbt_launch_dir/$1/sbt-launch.jar" \
+  || echo "$sbt_launch_dir/$1/sbt-launch.jar"
+}
+
+download_url () {
+  local url="$1"
+  local jar="$2"
+
+  echoerr "Downloading sbt launcher for $sbt_version:"
+  echoerr "  From  $url"
+  echoerr "    To  $jar"
+
+  mkdir -p "${jar%/*}" && {
+    if command -v curl > /dev/null 2>&1; then
+      curl --fail --silent --location "$url" --output "$jar"
+    elif command -v wget > /dev/null 2>&1; then
+      wget -q -O "$jar" "$url"
+    fi
+  } && [[ -r "$jar" ]]
+}
+
+acquire_sbt_jar () {
+  {
+    sbt_jar="$(jar_file "$sbt_version")"
+    [[ -r "$sbt_jar" ]]
+  } || {
+    sbt_jar="$HOME/.ivy2/local/org.scala-sbt/sbt-launch/$sbt_version/jars/sbt-launch.jar"
+    [[ -r "$sbt_jar" ]]
+  } || {
+    sbt_jar="$(jar_file "$sbt_version")"
+    download_url "$(make_url "$sbt_version")" "$sbt_jar"
+  }
+}
+
+usage () {
+  set_sbt_version
+  cat <<EOM
+Usage: $script_name [options]
+Note that options which are passed along to sbt begin with -- whereas
+options to this runner use a single dash. Any sbt command can be scheduled
+to run first by prefixing the command with --, so --warn, --error and so on
+are not special.
+Output filtering: if there is a file in the home directory called .sbtignore
+and this is not an interactive sbt session, the file is treated as a list of
+bash regular expressions. Output lines which match any regex are not echoed.
+One can see exactly which lines would have been suppressed by starting this
+runner with the -x option.
+  -h | -help         print this message
+  -v                 verbose operation (this runner is chattier)
+  -d, -w, -q         aliases for --debug, --warn, --error (q means quiet)
+  -x                 debug this script
+  -trace <level>     display stack traces with a max of <level> frames (default: -1, traces suppressed)
+  -debug-inc         enable debugging log for the incremental compiler
+  -no-colors         disable ANSI color codes
+  -sbt-create        start sbt even if current directory contains no sbt project
+  -sbt-dir   <path>  path to global settings/plugins directory (default: ~/.sbt/<version>)
+  -sbt-boot  <path>  path to shared boot directory (default: ~/.sbt/boot in 0.11+)
+  -ivy       <path>  path to local Ivy repository (default: ~/.ivy2)
+  -no-share          use all local caches; no sharing
+  -offline           put sbt in offline mode
+  -jvm-debug <port>  Turn on JVM debugging, open at the given port.
+  -batch             Disable interactive mode
+  -prompt <expr>     Set the sbt prompt; in expr, 's' is the State and 'e' is Extracted
+  -script <file>     Run the specified file as a scala script
+  # sbt version (default: sbt.version from $buildProps if present, otherwise $sbt_release_version)
+  -sbt-force-latest         force the use of the latest release of sbt: $sbt_release_version
+  -sbt-version  <version>   use the specified version of sbt (default: $sbt_release_version)
+  -sbt-dev                  use the latest pre-release version of sbt: $sbt_unreleased_version
+  -sbt-jar      <path>      use the specified jar as the sbt launcher
+  -sbt-launch-dir <path>    directory to hold sbt launchers (default: $sbt_launch_dir)
+  -sbt-launch-repo <url>    repo url for downloading sbt launcher jar (default: $(url_base "$sbt_version"))
+  # scala version (default: as chosen by sbt)
+  -28                       use $latest_28
+  -29                       use $latest_29
+  -210                      use $latest_210
+  -211                      use $latest_211
+  -212                      use $latest_212
+  -213                      use $latest_213
+  -scala-home <path>        use the scala build at the specified directory
+  -scala-version <version>  use the specified version of scala
+  -binary-version <version> use the specified scala version when searching for dependencies
+  # java version (default: java from PATH, currently $(java -version 2>&1 | grep version))
+  -java-home <path>         alternate JAVA_HOME
+  # passing options to the jvm - note it does NOT use JAVA_OPTS due to pollution
+  # The default set is used if JVM_OPTS is unset and no -jvm-opts file is found
+  <default>        $(default_jvm_opts)
+  JVM_OPTS         environment variable holding either the jvm args directly, or
+                   the reference to a file containing jvm args if given path is prepended by '@' (e.g. '@/etc/jvmopts')
+                   Note: "@"-file is overridden by local '.jvmopts' or '-jvm-opts' argument.
+  -jvm-opts <path> file containing jvm args (if not given, .jvmopts in project root is used if present)
+  -Dkey=val        pass -Dkey=val directly to the jvm
+  -J-X             pass option -X directly to the jvm (-J is stripped)
+  # passing options to sbt, OR to this runner
+  SBT_OPTS         environment variable holding either the sbt args directly, or
+                   the reference to a file containing sbt args if given path is prepended by '@' (e.g. '@/etc/sbtopts')
+                   Note: "@"-file is overridden by local '.sbtopts' or '-sbt-opts' argument.
+  -sbt-opts <path> file containing sbt args (if not given, .sbtopts in project root is used if present)
+  -S-X             add -X to sbt's scalacOptions (-S is stripped)
+EOM
+}
+
+process_args () {
+  require_arg () {
+    local type="$1"
+    local opt="$2"
+    local arg="$3"
+
+    if [[ -z "$arg" ]] || [[ "${arg:0:1}" == "-" ]]; then
+      die "$opt requires <$type> argument"
+    fi
+  }
+  while [[ $# -gt 0 ]]; do
+    case "$1" in
+          -h|-help) usage; exit 0 ;;
+                -v) verbose=true && shift ;;
+                -d) addSbt "--debug" && shift ;;
+                -w) addSbt "--warn"  && shift ;;
+                -q) addSbt "--error" && shift ;;
+                -x) debugUs=true && shift ;;
+            -trace) require_arg integer "$1" "$2" && trace_level="$2" && shift 2 ;;
+              -ivy) require_arg path "$1" "$2" && addJava "-Dsbt.ivy.home=$2" && shift 2 ;;
+        -no-colors) addJava "-Dsbt.log.noformat=true" && shift ;;
+         -no-share) noshare=true && shift ;;
+         -sbt-boot) require_arg path "$1" "$2" && addJava "-Dsbt.boot.directory=$2" && shift 2 ;;
+          -sbt-dir) require_arg path "$1" "$2" && sbt_dir="$2" && shift 2 ;;
+        -debug-inc) addJava "-Dxsbt.inc.debug=true" && shift ;;
+          -offline) addSbt "set offline in Global := true" && shift ;;
+        -jvm-debug) require_arg port "$1" "$2" && addDebugger "$2" && shift 2 ;;
+            -batch) batch=true && shift ;;
+           -prompt) require_arg "expr" "$1" "$2" && setThisBuild shellPrompt "(s => { val e = Project.extract(s) ; $2 })" && shift 2 ;;
+           -script) require_arg file "$1" "$2" && sbt_script="$2" && addJava "-Dsbt.main.class=sbt.ScriptMain" && shift 2 ;;
+
+       -sbt-create) sbt_create=true && shift ;;
+          -sbt-jar) require_arg path "$1" "$2" && sbt_jar="$2" && shift 2 ;;
+      -sbt-version) require_arg version "$1" "$2" && sbt_explicit_version="$2" && shift 2 ;;
+ -sbt-force-latest) sbt_explicit_version="$sbt_release_version" && shift ;;
+          -sbt-dev) sbt_explicit_version="$sbt_unreleased_version" && shift ;;
+   -sbt-launch-dir) require_arg path "$1" "$2" && sbt_launch_dir="$2" && shift 2 ;;
+  -sbt-launch-repo) require_arg path "$1" "$2" && sbt_launch_repo="$2" && shift 2 ;;
+    -scala-version) require_arg version "$1" "$2" && setScalaVersion "$2" && shift 2 ;;
+   -binary-version) require_arg version "$1" "$2" && setThisBuild scalaBinaryVersion "\"$2\"" && shift 2 ;;
+       -scala-home) require_arg path "$1" "$2" && setThisBuild scalaHome "_root_.scala.Some(file(\"$2\"))" && shift 2 ;;
+        -java-home) require_arg path "$1" "$2" && setJavaHome "$2" && shift 2 ;;
+         -sbt-opts) require_arg path "$1" "$2" && sbt_opts_file="$2" && shift 2 ;;
+         -jvm-opts) require_arg path "$1" "$2" && jvm_opts_file="$2" && shift 2 ;;
+
+               -D*) addJava "$1" && shift ;;
+               -J*) addJava "${1:2}" && shift ;;
+               -S*) addScalac "${1:2}" && shift ;;
+               -28) setScalaVersion "$latest_28" && shift ;;
+               -29) setScalaVersion "$latest_29" && shift ;;
+              -210) setScalaVersion "$latest_210" && shift ;;
+              -211) setScalaVersion "$latest_211" && shift ;;
+              -212) setScalaVersion "$latest_212" && shift ;;
+              -213) setScalaVersion "$latest_213" && shift ;;
+               new) sbt_new=true && : ${sbt_explicit_version:=$sbt_release_version} && addResidual "$1" && shift ;;
+                 *) addResidual "$1" && shift ;;
+    esac
+  done
+}
+
+# process the direct command line arguments
+process_args "$@"
+
+# skip #-styled comments and blank lines
+readConfigFile() {
+  local end=false
+  until $end; do
+    read -r || end=true
+    [[ $REPLY =~ ^# ]] || [[ -z $REPLY ]] || echo "$REPLY"
+  done < "$1"
+}
+
+# if there are file/environment sbt_opts, process again so we
+# can supply args to this runner
+if [[ -r "$sbt_opts_file" ]]; then
+  vlog "Using sbt options defined in file $sbt_opts_file"
+  while read -r opt; do extra_sbt_opts+=("$opt"); done < <(readConfigFile "$sbt_opts_file")
+elif [[ -n "$SBT_OPTS" && ! ("$SBT_OPTS" =~ ^@.*) ]]; then
+  vlog "Using sbt options defined in variable \$SBT_OPTS"
+  IFS=" " read -r -a extra_sbt_opts <<< "$SBT_OPTS"
+else
+  vlog "No extra sbt options have been defined"
+fi
+
+[[ -n "${extra_sbt_opts[*]}" ]] && process_args "${extra_sbt_opts[@]}"
+
+# reset "$@" to the residual args
+set -- "${residual_args[@]}"
+argumentCount=$#
+
+# set sbt version
+set_sbt_version
+
+checkJava
+
+# only exists in 0.12+
+setTraceLevel() {
+  case "$sbt_version" in
+    "0.7."* | "0.10."* | "0.11."* ) echoerr "Cannot set trace level in sbt version $sbt_version" ;;
+                                 *) setThisBuild traceLevel "$trace_level" ;;
+  esac
+}
+
+# set scalacOptions if we were given any -S opts
+[[ ${#scalac_args[@]} -eq 0 ]] || addSbt "set scalacOptions in ThisBuild += \"${scalac_args[*]}\""
+
+[[ -n "$sbt_explicit_version" && -z "$sbt_new" ]] && addJava "-Dsbt.version=$sbt_explicit_version"
+vlog "Detected sbt version $sbt_version"
+
+if [[ -n "$sbt_script" ]]; then
+  residual_args=( "$sbt_script" "${residual_args[@]}" )
+else
+  # no args - alert them there's stuff in here
+  (( argumentCount > 0 )) || {
+    vlog "Starting $script_name: invoke with -help for other options"
+    residual_args=( shell )
+  }
+fi
+
+# verify this is an sbt dir, -create was given or user attempts to run a scala script
+[[ -r ./build.sbt || -d ./project || -n "$sbt_create" || -n "$sbt_script" || -n "$sbt_new" ]] || {
+  cat <<EOM
+$(pwd) doesn't appear to be an sbt project.
+If you want to start sbt anyway, run:
+  $0 -sbt-create
+EOM
+  exit 1
+}
+
+# pick up completion if present; todo
+# shellcheck disable=SC1091
+[[ -r .sbt_completion.sh ]] && source .sbt_completion.sh
+
+# directory to store sbt launchers
+[[ -d "$sbt_launch_dir" ]] || mkdir -p "$sbt_launch_dir"
+[[ -w "$sbt_launch_dir" ]] || sbt_launch_dir="$(mktemp -d -t sbt_extras_launchers.XXXXXX)"
+
+# no jar? download it.
+[[ -r "$sbt_jar" ]] || acquire_sbt_jar || {
+  # still no jar? uh-oh.
+  echo "Download failed. Obtain the jar manually and place it at $sbt_jar"
+  exit 1
+}
+
+if [[ -n "$noshare" ]]; then
+  for opt in ${noshare_opts}; do
+    addJava "$opt"
+  done
+else
+  case "$sbt_version" in
+    "0.7."* | "0.10."* | "0.11."* | "0.12."* )
+      [[ -n "$sbt_dir" ]] || {
+        sbt_dir="$HOME/.sbt/$sbt_version"
+        vlog "Using $sbt_dir as sbt dir, -sbt-dir to override."
+      }
+    ;;
+  esac
+
+  if [[ -n "$sbt_dir" ]]; then
+    addJava "-Dsbt.global.base=$sbt_dir"
+  fi
+fi
+
+if [[ -r "$jvm_opts_file" ]]; then
+  vlog "Using jvm options defined in file $jvm_opts_file"
+  while read -r opt; do extra_jvm_opts+=("$opt"); done < <(readConfigFile "$jvm_opts_file")
+elif [[ -n "$JVM_OPTS" && ! ("$JVM_OPTS" =~ ^@.*) ]]; then
+  vlog "Using jvm options defined in \$JVM_OPTS variable"
+  IFS=" " read -r -a extra_jvm_opts <<< "$JVM_OPTS"
+else
+  vlog "Using default jvm options"
+  IFS=" " read -r -a extra_jvm_opts <<< "$(default_jvm_opts)"
+fi
+
+# traceLevel is 0.12+
+[[ -n "$trace_level" ]] && setTraceLevel
+
+main () {
+  execRunner "$java_cmd" \
+    "${extra_jvm_opts[@]}" \
+    "${java_args[@]}" \
+    -jar "$sbt_jar" \
+    "${sbt_commands[@]}" \
+    "${residual_args[@]}"
+}
+
+# sbt inserts this string on certain lines when formatting is enabled:
+#   val OverwriteLine = "\r\u001BM\u001B[2K"
+# ...in order not to spam the console with a million "Resolving" lines.
+# Unfortunately that makes it that much harder to work with when
+# we're not going to print those lines anyway. We strip that bit of
+# line noise, but leave the other codes to preserve color.
+mainFiltered () {
+  local -r excludeRegex=$(grep -E -v '^#|^$' ~/.sbtignore | paste -sd'|' -)
+
+  echoLine () {
+    local -r line="$1"
+    local -r line1="${line//\r\x1BM\x1B\[2K//g}"       # This strips the OverwriteLine code.
+    local -r line2="${line1//\x1B\[[0-9;]*[JKmsu]//g}" # This strips all codes - we test regexes against this.
+
+    if [[ $line2 =~ $excludeRegex ]]; then
+      [[ -n $debugUs ]] && echo "[X] $line1"
+    else
+      [[ -n $debugUs ]] && echo "    $line1" || echo "$line1"
+    fi
+  }
+
+  echoLine "Starting sbt with output filtering enabled."
+  main | while read -r line; do echoLine "$line"; done
+}
+
+# Only filter if there's a filter file and we don't see a known interactive command.
+# Obviously this is super ad hoc but I don't know how to improve on it. Testing whether
+# stdin is a terminal is useless because most of my use cases for this filtering are
+# exactly when I'm at a terminal, running sbt non-interactively.
+shouldFilter () { [[ -f ~/.sbtignore ]] && ! grep -E -q '\b(shell|console|consoleProject)\b' <<<"${residual_args[@]}"; }
+
+# run sbt
+if shouldFilter; then mainFiltered; else main; fi