FreeMASTER Web Application

Builds browser-based or Node.js applications that talk to a running FreeMASTER Lite instance through the freemaster-client.js library and its PCM API. The web app must be served from the FreeMASTER Lite web_root so the browser can load the client libraries from the same origin.

When to use

• Building an HTML, JavaScript, or Node.js client for FreeMASTER Lite.
• Using freemaster-client.js, simple-jsonrpc-js.js, or the PCM API.
• Reading or writing variables from a browser-side application.
• Hosting the app in FreeMASTER Lite web_root.

Do not use this skill for direct MCP JSON-RPC calls (freemaster-lite-jsonrpc-api), .fmcfg file creation (freemaster-lite-configuration-file), or launching the service (freemaster-lite-start-server).

Quick start

<script src="/simple-jsonrpc-js.js"></script>
<script src="/freemaster-client.js"></script>
<script>
  var pcm;
  window.onload = function() {
    pcm = new PCM('127.0.0.1:8090', function() {
      pcm.StartComm('RS232;port=COM3;speed=115200')
        .then(function() { return pcm.IsBoardDetected(); })
        .then(function() { return pcm.ReadVariable('g_speed'); })
        .then(function(r) { console.log('speed:', r.data); })
        .catch(function(e) { console.error(e); });
    });
  };
</script>

Both libraries are served automatically at http://localhost:8090/ when FreeMASTER Lite is running. Files in the configured web_root override the built-in copies.

Step-by-step Workflow

1. Include libraries

<script type="text/javascript" src="/simple-jsonrpc-js.js"></script>
<script type="text/javascript" src="/freemaster-client.js"></script>

2. Instantiate PCM

pcm = new PCM('127.0.0.1:8090', on_connect);

First argument: host:port (not a full URL). Second argument: callback invoked when the WebSocket connection to FreeMASTER Lite is established.

3. Check board and load symbols

Inside on_connect, start communication and confirm the board is detected before reading variables:

function on_connect() {
  pcm.StartComm('RS232;port=COM3;speed=115200')
    .then(() => pcm.IsBoardDetected())
    .then(() => pcm.ReadELF())           // or pcm.ReadTSA()
    .then(() => pcm.ReadVariable('g_motorSpeed'))
    .then(r => console.log('speed:', r.data))
    .catch(e => console.error(e));
}

All PCM methods return a Promise. Actual data is in response.data.

PCM API Summary

Category	Key methods
Communication	StartComm, StopComm, IsCommPortOpen, EnumCommPorts
Board	IsBoardDetected, GetDetectedBoardInfo
Symbols	ReadELF, ReadTSA, EnumSymbols, GetSymbolInfo
Variables	DefineVariable, GetVariableInfo, EnumVariables, ReadVariable, WriteVariable, DeleteVariable
Oscilloscope	SetupOscilloscope, GetOscilloscopeData
Recorder	SetupRecorder, StartRecorder, StopRecorder, GetRecorderData

See references/examples.md for periodic polling, async/await, dynamic variable definition, and Node.js npm usage patterns.

Guardrails

Scope

• This skill covers browser-side and Node.js application code only.
• The web app must reside in or be served from the FreeMASTER Lite web_root; cross-origin setups require additional server configuration outside this skill.

Destructive actions

• WriteVariable modifies live target memory. Confirm the target variable and value with the user before writing, especially for safety-critical state.

Secrets

• No credentials involved. If SSL is enabled in .fmcfg, the browser connects over wss:// automatically.

Refuse-and-escalate

• If IsBoardDetected fails after StartComm, stop and direct the user to check the .fmcfg connection settings and target hardware before continuing to variable access.

Validation loop

1. Open the app in a browser; confirm no 404 errors for the client library scripts.
2. on_connect callback must fire — if it does not, the PCM WebSocket connection to FreeMASTER Lite failed.
3. IsBoardDetected must resolve (not reject) before variable access.
4. ReadVariable result response.data must be a number, not undefined.
5. After WriteVariable, read back the value to confirm the write succeeded.

Out of scope

• Direct MCP JSON-RPC calls — use freemaster-lite-jsonrpc-api.
• Building the FreeMASTER Lite service or .fmcfg — use freemaster-lite-start-server and freemaster-lite-configuration-file.
• Generic web application help unrelated to FreeMASTER Lite.

See Also

• references/examples.md — complete HTML page, polling, async/await, Node.js, and mock-API usage patterns
• freemaster-lite-start-server — launch FreeMASTER Lite before loading the app
• freemaster-lite-configuration-file — configure web_root and connections
• freemaster-lite-jsonrpc-api — low-level MCP JSON-RPC alternative
• freemaster-lite-command-line-arguments — --mock_api and --web_root flags