feat: basic msp encode/decode

.github/workflows/test.yml

···
+name: test
+
+on:
+  push:
+    branches:
+      - master
+      - main
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: "28"
+          gleam-version: "1.13.0"
+          rebar3-version: "3"
+          # elixir-version: "1"
+      - run: gleam deps download
+      - run: gleam test
+      - run: gleam format --check src test

.gitignore

···
+*.beam
+*.ez
+/build
+erl_crash.dump
+
+#Added automatically by Lustre Dev Tools
+/.lustre
+/dist

.mise.toml

···
+[tools]
+bun = "latest"
+gleam = "latest"
+erlang = "latest"
+rebar = "latest"

README.md

···
+# betaflight_wizard
+
+[![Package Version](https://img.shields.io/hexpm/v/betaflight_wizard)](https://hex.pm/packages/betaflight_wizard)
+[![Hex Docs](https://img.shields.io/badge/hex-docs-ffaff3)](https://hexdocs.pm/betaflight_wizard/)
+
+```sh
+gleam add betaflight_wizard@1
+```
+```gleam
+import betaflight_wizard
+
+pub fn main() -> Nil {
+  // TODO: An example of the project in use
+}
+```
+
+Further documentation can be found at <https://hexdocs.pm/betaflight_wizard>.
+
+## Development
+
+```sh
+gleam run   # Run the project
+gleam test  # Run the tests
+```

gleam.toml

···
+name = "betaflight_wizard"
+version = "1.0.0"
+
+target = "javascript"
+
+[dependencies]
+gleam_stdlib = ">= 0.44.0 and < 2.0.0"
+lustre = ">= 5.4.0 and < 6.0.0"
+
+[dev-dependencies]
+gleeunit = ">= 1.0.0 and < 2.0.0"
+lustre_dev_tools = ">= 2.3.1 and < 3.0.0"
+
+[tools.lustre]
+bin.bun = "system"

manifest.toml

···
+# This file was generated by Gleam
+# You typically do not need to edit this file
+
+packages = [
+  { name = "argv", version = "1.0.2", build_tools = ["gleam"], requirements = [], otp_app = "argv", source = "hex", outer_checksum = "BA1FF0929525DEBA1CE67256E5ADF77A7CDDFE729E3E3F57A5BDCAA031DED09D" },
+  { name = "booklet", version = "1.1.0", build_tools = ["gleam"], requirements = [], otp_app = "booklet", source = "hex", outer_checksum = "08E0FDB78DC4D8A5D3C80295B021505C7D2A2E7B6C6D5EAB7286C36F4A53C851" },
+  { name = "directories", version = "1.2.0", build_tools = ["gleam"], requirements = ["envoy", "gleam_stdlib", "platform", "simplifile"], otp_app = "directories", source = "hex", outer_checksum = "D13090CFCDF6759B87217E8DDD73A75903A700148A82C1D33799F333E249BF9E" },
+  { name = "envoy", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "envoy", source = "hex", outer_checksum = "850DA9D29D2E5987735872A2B5C81035146D7FE19EFC486129E44440D03FD832" },
+  { name = "exception", version = "2.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "exception", source = "hex", outer_checksum = "329D269D5C2A314F7364BD2711372B6F2C58FA6F39981572E5CA68624D291F8C" },
+  { name = "filepath", version = "1.1.2", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "filepath", source = "hex", outer_checksum = "B06A9AF0BF10E51401D64B98E4B627F1D2E48C154967DA7AF4D0914780A6D40A" },
+  { name = "gleam_community_ansi", version = "1.4.3", build_tools = ["gleam"], requirements = ["gleam_community_colour", "gleam_regexp", "gleam_stdlib"], otp_app = "gleam_community_ansi", source = "hex", outer_checksum = "8A62AE9CC6EA65BEA630D95016D6C07E4F9973565FA3D0DE68DC4200D8E0DD27" },
+  { name = "gleam_community_colour", version = "2.0.2", build_tools = ["gleam"], requirements = ["gleam_json", "gleam_stdlib"], otp_app = "gleam_community_colour", source = "hex", outer_checksum = "E34DD2C896AC3792151EDA939DA435FF3B69922F33415ED3C4406C932FBE9634" },
+  { name = "gleam_crypto", version = "1.5.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_crypto", source = "hex", outer_checksum = "50774BAFFF1144E7872814C566C5D653D83A3EBF23ACC3156B757A1B6819086E" },
+  { name = "gleam_erlang", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "1124AD3AA21143E5AF0FC5CF3D9529F6DB8CA03E43A55711B60B6B7B3874375C" },
+  { name = "gleam_http", version = "4.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_http", source = "hex", outer_checksum = "82EA6A717C842456188C190AFB372665EA56CE13D8559BF3B1DD9E40F619EE0C" },
+  { name = "gleam_httpc", version = "5.0.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_http", "gleam_stdlib"], otp_app = "gleam_httpc", source = "hex", outer_checksum = "C545172618D07811494E97AAA4A0FB34DA6F6D0061FDC8041C2F8E3BE2B2E48F" },
+  { name = "gleam_json", version = "3.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_json", source = "hex", outer_checksum = "44FDAA8847BE8FC48CA7A1C089706BD54BADCC4C45B237A992EDDF9F2CDB2836" },
+  { name = "gleam_otp", version = "1.2.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_stdlib"], otp_app = "gleam_otp", source = "hex", outer_checksum = "BA6A294E295E428EC1562DC1C11EA7530DCB981E8359134BEABC8493B7B2258E" },
+  { name = "gleam_regexp", version = "1.1.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_regexp", source = "hex", outer_checksum = "9C215C6CA84A5B35BB934A9B61A9A306EC743153BE2B0425A0D032E477B062A9" },
+  { name = "gleam_stdlib", version = "0.67.1", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "6CE3E4189A8B8EC2F73AB61A2FBDE49F159D6C9C61C49E3B3082E439F260D3D0" },
+  { name = "gleam_time", version = "1.6.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_time", source = "hex", outer_checksum = "0DF3834D20193F0A38D0EB21F0A78D48F2EC276C285969131B86DF8D4EF9E762" },
+  { name = "gleam_yielder", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_yielder", source = "hex", outer_checksum = "8E4E4ECFA7982859F430C57F549200C7749823C106759F4A19A78AEA6687717A" },
+  { name = "gleeunit", version = "1.9.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "DA9553CE58B67924B3C631F96FE3370C49EB6D6DC6B384EC4862CC4AAA718F3C" },
+  { name = "glint", version = "1.2.1", build_tools = ["gleam"], requirements = ["gleam_community_ansi", "gleam_community_colour", "gleam_stdlib", "snag"], otp_app = "glint", source = "hex", outer_checksum = "2214C7CEFDE457CEE62140C3D4899B964E05236DA74E4243DFADF4AF29C382BB" },
+  { name = "glisten", version = "8.0.1", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_otp", "gleam_stdlib", "logging", "telemetry"], otp_app = "glisten", source = "hex", outer_checksum = "534BB27C71FB9E506345A767C0D76B17A9E9199934340C975DC003C710E3692D" },
+  { name = "gramps", version = "6.0.0", build_tools = ["gleam"], requirements = ["gleam_crypto", "gleam_erlang", "gleam_http", "gleam_stdlib"], otp_app = "gramps", source = "hex", outer_checksum = "8B7195978FBFD30B43DF791A8A272041B81E45D245314D7A41FC57237AA882A0" },
+  { name = "group_registry", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_otp", "gleam_stdlib"], otp_app = "group_registry", source = "hex", outer_checksum = "BC798A53D6F2406DB94E27CB45C57052CB56B32ACF7CC16EA20F6BAEC7E36B90" },
+  { name = "houdini", version = "1.2.0", build_tools = ["gleam"], requirements = [], otp_app = "houdini", source = "hex", outer_checksum = "5DB1053F1AF828049C2B206D4403C18970ABEF5C18671CA3C2D2ED0DD64F6385" },
+  { name = "hpack_erl", version = "0.3.0", build_tools = ["rebar3"], requirements = [], otp_app = "hpack", source = "hex", outer_checksum = "D6137D7079169D8C485C6962DFE261AF5B9EF60FBC557344511C1E65E3D95FB0" },
+  { name = "justin", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "justin", source = "hex", outer_checksum = "7FA0C6DB78640C6DC5FBFD59BF3456009F3F8B485BF6825E97E1EB44E9A1E2CD" },
+  { name = "logging", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "logging", source = "hex", outer_checksum = "1098FBF10B54B44C2C7FDF0B01C1253CAFACDACABEFB4B0D027803246753E06D" },
+  { name = "lustre", version = "5.4.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_json", "gleam_otp", "gleam_stdlib", "houdini"], otp_app = "lustre", source = "hex", outer_checksum = "40E097BABCE65FB7C460C073078611F7F5802EB07E1A9BFB5C229F71B60F8E50" },
+  { name = "lustre_dev_tools", version = "2.3.1", build_tools = ["gleam"], requirements = ["argv", "booklet", "filepath", "gleam_community_ansi", "gleam_crypto", "gleam_erlang", "gleam_http", "gleam_httpc", "gleam_json", "gleam_otp", "gleam_regexp", "gleam_stdlib", "glint", "group_registry", "justin", "lustre", "mist", "polly", "simplifile", "tom", "wisp"], otp_app = "lustre_dev_tools", source = "hex", outer_checksum = "2C8C646FF45087C31C2DE8088C2F6DB26E8CEE52B3A883F47F6B2C4F5A16C9C6" },
+  { name = "marceau", version = "1.3.0", build_tools = ["gleam"], requirements = [], otp_app = "marceau", source = "hex", outer_checksum = "2D1C27504BEF45005F5DFB18591F8610FB4BFA91744878210BDC464412EC44E9" },
+  { name = "mist", version = "5.0.3", build_tools = ["gleam"], requirements = ["exception", "gleam_erlang", "gleam_http", "gleam_otp", "gleam_stdlib", "gleam_yielder", "glisten", "gramps", "hpack_erl", "logging"], otp_app = "mist", source = "hex", outer_checksum = "7C4BE717A81305323C47C8A591E6B9BA4AC7F56354BF70B4D3DF08CC01192668" },
+  { name = "platform", version = "1.0.0", build_tools = ["gleam"], requirements = [], otp_app = "platform", source = "hex", outer_checksum = "8339420A95AD89AAC0F82F4C3DB8DD401041742D6C3F46132A8739F6AEB75391" },
+  { name = "polly", version = "2.1.0", build_tools = ["gleam"], requirements = ["filepath", "gleam_stdlib", "simplifile"], otp_app = "polly", source = "hex", outer_checksum = "1BA4D0ACE9BCF52AEA6AD9DE020FD8220CCA399A379E50A1775FC5C1204FCF56" },
+  { name = "simplifile", version = "2.3.1", build_tools = ["gleam"], requirements = ["filepath", "gleam_stdlib"], otp_app = "simplifile", source = "hex", outer_checksum = "957E0E5B75927659F1D2A1B7B75D7B9BA96FAA8D0C53EA71C4AD9CD0C6B848F6" },
+  { name = "snag", version = "1.2.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "snag", source = "hex", outer_checksum = "274F41D6C3ECF99F7686FDCE54183333E41D2C1CA5A3A673F9A8B2C7A4401077" },
+  { name = "telemetry", version = "1.3.0", build_tools = ["rebar3"], requirements = [], otp_app = "telemetry", source = "hex", outer_checksum = "7015FC8919DBE63764F4B4B87A95B7C0996BD539E0D499BE6EC9D7F3875B79E6" },
+  { name = "tom", version = "2.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib", "gleam_time"], otp_app = "tom", source = "hex", outer_checksum = "74D0C5A3761F7A7D06994755D4D5AD854122EF8E9F9F76A3E7547606D8C77091" },
+  { name = "wisp", version = "2.1.0", build_tools = ["gleam"], requirements = ["directories", "exception", "filepath", "gleam_crypto", "gleam_erlang", "gleam_http", "gleam_json", "gleam_stdlib", "houdini", "logging", "marceau", "mist", "simplifile"], otp_app = "wisp", source = "hex", outer_checksum = "362BDDD11BF48EB38CDE51A73BC7D1B89581B395CA998E3F23F11EC026151C54" },
+]
+
+[requirements]
+gleam_stdlib = { version = ">= 0.44.0 and < 2.0.0" }
+gleeunit = { version = ">= 1.0.0 and < 2.0.0" }
+lustre = { version = ">= 5.4.0 and < 6.0.0" }
+lustre_dev_tools = { version = ">= 2.3.1 and < 3.0.0" }

src/betaflight_wizard.gleam

···
+import gleam/io
+import lustre/element/html
+
+import lustre
+import lustre/element.{type Element}
+
+pub fn main() -> Nil {
+  let app = lustre.simple(init, update, view)
+  let assert Ok(_) = lustre.start(app, "#app", Nil)
+
+  Nil
+}
+
+type Model =
+  Int
+
+fn init(_args) -> Model {
+  0
+}
+
+type Msg {
+  UserClicked
+}
+
+fn update(model: Model, msg: Msg) -> Model {
+  case msg {
+    UserClicked -> model + 1
+  }
+}
+
+fn view(model: Model) -> Element(msg) {
+  html.div([], [
+    html.h1([], [html.text("Waiting for FC...")]),
+    html.button([], [html.text("Select your port")]),
+  ])
+}

src/betaflight_wizard/msp/msp.gleam

···
+import gleam/bit_array
+import gleam/bool
+import gleam/int
+import gleam/io
+import gleam/string
+
+const baud_rates = [
+  "AUTO",
+  "9600",
+  "19200",
+  "38400",
+  "57600",
+  "115200",
+  "230400",
+  "250000",
+  "400000",
+  "460800",
+  "500000",
+  "921600",
+  "1000000",
+  "1500000",
+  "2000000",
+  "2470000",
+]
+
+pub type PacketDirection {
+  ToFc
+  FromFc
+  ErrorReport
+}
+
+pub type Packet {
+  Packet
+}
+
+pub type ParseError {
+  Incomplete
+  Crc(expected: Int, actual: Int)
+}
+
+@internal
+pub fn calculate_crc_v1(
+  size size: Int,
+  cmd cmd: Int,
+  data data: BitArray,
+  crc crc: Int,
+) -> Int {
+  case data {
+    <<b:size(8), rest:bytes>> ->
+      calculate_crc_v1(size, cmd, rest, int.bitwise_exclusive_or(crc, b))
+    <<b:size(8)>> ->
+      calculate_crc_v1(size, cmd, <<>>, int.bitwise_exclusive_or(crc, b))
+    _ ->
+      size
+      |> int.bitwise_exclusive_or(cmd)
+      |> int.bitwise_exclusive_or(crc)
+  }
+}
+
+@internal
+pub fn calculate_crc_v2(
+  size size: Int,
+  flag flag: Int,
+  cmd cmd: Int,
+  data data: BitArray,
+) -> Int {
+  0
+  |> crc_dvb_s2(flag)
+  |> crc_dvb_s2(int.bitwise_and(cmd, 0xff))
+  |> crc_dvb_s2(cmd |> int.bitwise_and(0xff00) |> int.bitwise_shift_right(8))
+  |> crc_dvb_s2(int.bitwise_and(size, 0xff))
+  |> crc_dvb_s2(size |> int.bitwise_and(0xff00) |> int.bitwise_shift_right(8))
+  |> calculate_crc_v2_loop(data)
+}
+
+fn calculate_crc_v2_loop(crc: Int, data: BitArray) -> Int {
+  case data {
+    <<>> -> crc
+    <<b:size(8)>> -> crc_dvb_s2(crc, b)
+    <<b:size(8), rest:bytes>> ->
+      crc_dvb_s2(crc, b) |> calculate_crc_v2_loop(rest)
+    what ->
+      panic as {
+        "OOPS got invalid state while calculating crcv2 "
+        <> string.inspect(what)
+      }
+  }
+}
+
+// what?
+fn crc_dvb_s2(crc: Int, byte: Int) -> Int {
+  let crc = int.bitwise_exclusive_or(crc, byte)
+  crc_dvb_s2_loop(crc, 0)
+}
+
+fn crc_dvb_s2_loop(crc: Int, i: Int) -> Int {
+  case i {
+    8 -> crc
+    i -> {
+      case int.bitwise_and(crc, 0x80) == 0 {
+        True -> crc |> int.bitwise_shift_left(1) |> int.bitwise_and(0xff)
+        False ->
+          crc
+          |> int.bitwise_shift_left(1)
+          |> int.bitwise_and(0xff)
+          |> int.bitwise_exclusive_or(0xd5)
+      }
+    }
+  }
+}
+
+fn parse_direction(dir: Int) -> Result(PacketDirection, Nil) {
+  case dir {
+    // <
+    0x3c -> Ok(ToFc)
+    // >
+    0x3e -> Ok(FromFc)
+    // !
+    0x21 -> Ok(ErrorReport)
+    _ -> Error(Nil)
+  }
+}
+
+/// returns #(Result(Packet, ErrorReason), DataRest)
+fn parse_packet(packet: BitArray) -> #(Result(Packet, ParseError), BitArray) {
+  case packet {
+    // V1 Packet ($M header)
+    <<"$M":utf8, dir:size(8), size:size(8), cmd:int-size(8), rest:bits>> ->
+      case rest {
+        <<data:bits-size(size), crc:size(8), rest:bits>> -> {
+          let actual_crc =
+            calculate_crc_v1(cmd: cmd, size: size, data: data, crc: 0)
+          use <- bool.guard(when: crc != actual_crc, return: #(
+            Error(Crc(expected: crc, actual: actual_crc)),
+            rest,
+          ))
+          let assert Ok(dir) = parse_direction(dir)
+          io.println(
+            "got command "
+            <> int.to_string(cmd)
+            <> " with direction "
+            <> string.inspect(dir)
+            <> " with data "
+            <> string.inspect(data),
+          )
+          todo
+        }
+        _ -> #(Error(Incomplete), packet)
+      }
+    // V2 Packet ($X header)
+    <<
+      "$X":utf8,
+      dir:size(8),
+      flag:size(8),
+      cmd:little-size(16),
+      size:little-size(16),
+      rest:bits,
+    >> ->
+      case rest {
+        <<data:bits-size(size), crc:size(8), rest:bits>> -> {
+          let actual_crc = calculate_crc_v2(cmd:, size:, data:, flag:)
+          use <- bool.guard(when: crc != actual_crc, return: #(
+            Error(Crc(expected: crc, actual: actual_crc)),
+            rest,
+          ))
+          let assert Ok(dir) = parse_direction(dir)
+          io.println(
+            "got v2 command "
+            <> int.to_string(cmd)
+            <> " with direction "
+            <> string.inspect(dir)
+            <> " with data "
+            <> string.inspect(data),
+          )
+          todo
+        }
+        _ -> #(Error(Incomplete), packet)
+      }
+    <<b:size(8), rest:bits>> -> {
+      io.println_error("invalid packet, discarding byte " <> int.to_string(b))
+      parse_packet(rest)
+    }
+    _ -> #(Error(Incomplete), packet)
+  }
+}
+
+@internal
+pub fn encode_v1_raw(command: Int, data: BitArray) -> BitArray {
+  // preamble, direction, data size, command, data, crc
+  let size = bit_array.byte_size(data)
+  <<
+    "$M",
+    "<",
+    size,
+    command,
+    data:bits,
+    calculate_crc_v1(command, size, data, 0),
+  >>
+}
+
+@internal
+pub fn encode_v2_raw(
+  command command: Int,
+  flag flag: Int,
+  data data: BitArray,
+) -> BitArray {
+  // preamble, direction, flag, cmd, size, data, crc
+  let size = bit_array.byte_size(data)
+  <<
+    "$X",
+    "<",
+    flag,
+    command:little-size(16),
+    size:little-size(16),
+    data:bits,
+    calculate_crc_v2(size:, data:, flag:, cmd: command),
+  >>
+}

test/betaflight_wizard_test.gleam

···
+import gleeunit
+
+pub fn main() -> Nil {
+  gleeunit.main()
+}

test/msp_test.gleam

···
+import betaflight_wizard/msp/msp
+import gleam/bit_array
+import gleam/int
+
+pub fn msp_encode_v1_empty_test() {
+  do_msp_encode_v1_empty(0)
+}
+
+pub fn encode_random_v1_message_test() {
+  let op_code = int.random(256)
+  let input_data_length = 100 + int.random(100)
+  let input_data = fill_input_data(input_data_length, 0, <<>>)
+
+  let encoded = msp.encode_v1_raw(op_code, input_data)
+  let encoded_length = bit_array.byte_size(encoded)
+
+  assert bit_array.slice(encoded, 0, 3) == Ok(<<"$M":utf8, "<":utf8>>)
+  assert bit_array.slice(encoded, 3, 1) == Ok(<<input_data_length:size(8)>>)
+  assert bit_array.slice(encoded, 4, 1) == Ok(<<op_code:size(8)>>)
+  assert bit_array.slice(encoded, 5, input_data_length) == Ok(input_data)
+  assert bit_array.slice(encoded, encoded_length - 1, 1)
+    == Ok(<<
+      msp.calculate_crc_v1(input_data_length, op_code, input_data, 0):size(8),
+    >>)
+}
+
+pub fn msp_encode_v2_empty_test() {
+  do_msp_encode_v2_empty(0)
+}
+
+pub fn encode_random_v2_message_test() {
+  let op_code = int.random(65_536)
+  let flag = int.random(256)
+  let input_data_length = int.random(65_536)
+  let input_data = fill_input_data(input_data_length, 0, <<>>)
+
+  let encoded = msp.encode_v2_raw(command: op_code, flag:, data: input_data)
+  let encoded_length = bit_array.byte_size(encoded)
+
+  // preamble, direction, flag, cmd low, cmd high, size, data, crc
+  // preamble, direction
+  assert bit_array.slice(encoded, 0, 3) == Ok(<<"$X", "<">>)
+  // flag
+  assert bit_array.slice(encoded, 3, 1) == Ok(<<flag>>)
+  // cmd
+  assert bit_array.slice(encoded, 4, 2) == Ok(<<op_code:little-size(16)>>)
+  // size
+  assert bit_array.slice(encoded, 6, 2)
+    == Ok(<<input_data_length:little-size(16)>>)
+  // data 
+  assert bit_array.slice(encoded, 8, input_data_length) == Ok(input_data)
+  // crc
+  assert bit_array.slice(encoded, encoded_length - 1, 1)
+    == Ok(<<
+      msp.calculate_crc_v2(
+        size: input_data_length,
+        flag:,
+        cmd: op_code,
+        data: input_data,
+      ),
+    >>)
+}
+
+fn do_msp_encode_v1_empty(cmd: Int) {
+  case cmd {
+    256 -> Nil
+    _ -> {
+      let encoded = msp.encode_v1_raw(cmd, <<>>)
+      // preamble, direction, data size, command, data, crc
+      assert encoded == <<"$M", "<", 0, cmd, cmd>>
+      do_msp_encode_v1_empty(cmd + 1)
+    }
+  }
+}
+
+fn fill_input_data(input_data_length: Int, n: Int, data: BitArray) -> BitArray {
+  case n {
+    n if n >= input_data_length -> data
+    n ->
+      fill_input_data(input_data_length, n + 1, <<data:bits, int.random(256)>>)
+  }
+}
+
+fn do_msp_encode_v2_empty(cmd: Int) {
+  case cmd {
+    // MSPv2 commands are 16bit rather than 8bit
+    65_536 -> Nil
+    _ -> {
+      let encoded = msp.encode_v2_raw(command: cmd, flag: 0, data: <<>>)
+      // preamble, direction, flag, cmd low, cmd high, size, data, crc
+      assert encoded
+        == <<
+          "$X",
+          "<",
+          0,
+          cmd:little-size(16),
+          0:size(16),
+          // skip data
+          msp.calculate_crc_v2(size: 0, cmd: cmd, flag: 0, data: <<>>),
+        >>
+      do_msp_encode_v2_empty(cmd + 1)
+    }
+  }
+}