API Fundamentals: IP & Serial Commands, Drivers & Feedback Parsing

Est. 65 minCompetency: Use device APIs and drivers and parse feedback.

Learning objectives

Explain what an AV device API is.
Distinguish IP and serial command patterns.
Use a driver to encapsulate a device's command set.
Parse feedback strings into state.

Vocabulary

API: The set of commands and responses a device accepts and returns.
Driver: A module that wraps a device's command set so logic can use it generically.
Command string: The bytes sent to a device (e.g. 'PON\r' to power on).
Feedback parsing: Turning a device's response string into usable state.
Delimiter: A character marking the end of a command or response (e.g. \r or \n).

Lesson content

Every controllable device speaks an API: a set of commands it accepts and responses it returns. You program by sending commands and reading responses — over serial or IP.

Command patterns

Serial display:
  send  "PON\r"          // power on
  send  "POF\r"          // power off
  send  "INP 1\r"        // select input 1
  reply "OK"             // ack

IP codec (illustrative):
  send JSON  { "cmd": "dial", "uri": "meet@..." }
  reply JSON { "ok": true, "callId": 123 }

Drivers

A driver wraps a device's commands and feedback so your logic can say display.powerOn() instead of formatting strings.
Drivers handle delimiters, retries, and feedback parsing.
Use the manufacturer's driver where available; write a clean one if not.
Keep the driver's interface generic so you can swap device models with minimal logic changes.

Feedback parsing

1Read the response bytes as they arrive.
2Split on the delimiter to get complete messages.
3Match each message to a state field (power, input, volume).
4Update variables and the UI from the parsed state.

Field caution — partial messages

Serial/IP responses can arrive in fragments (one response split across packets). Buffer until the delimiter, then parse. Parsing a fragment drops state and causes the panel to lie.

Worked example

A display driver sends 'PON\r', waits for 'OK' or the power-state query response, sets displayPower = ON, and updates the panel. If no response in 3 seconds, it retries once, then reports a display error to the panel.

Implementation checklist

✓Device API documented per device.
✓Driver wraps commands and parsing; logic uses generic calls.
✓Feedback buffered until delimiter, then parsed.
✓Non-response handled with retry then error.

Downloadable study guide

study-guide.txtcopy-paste ready

01. API = commands + responses over serial or IP.
02. Driver wraps a device so logic calls display.powerOn(), not raw strings.
03. Buffer fragments until the delimiter; parse complete messages only.
04. Handle non-response with retry then a clear error state.