State-Machine Based Decimation Filter for LiDAR UART Streaming

Gian Fajardo, SPaRA Research

A state machine for reading a continuous stream of 5-byte UART messages from a LiDAR scanner into an embedded system — in real time, with configurable decimation. Rather than capturing everything and filtering later, this design processes bytes as they arrive and skips every Mth message on the fly. Five states handle the full lifecycle: idle, pattern detection, offset alignment, recording, and skipping. Built for embedded systems engineers, robotics researchers, and anyone working with sensor data pipelines where memory is constrained and throughput matters.

How to create a State-Machine Based Decimation Filter for LiDAR UART Streaming

To create a state-machine based decimation filter for LiDAR UART streaming, follow these steps:

01.

Define your states before your transitions

List every mode the system can be in: HOLD (idle), FIND_PATTERN (sync detection), ADD_OFFSET (byte alignment), RECORD (capture), SKIP (discard). Each state has exactly one job.

02.

Assign a limit to each state

Every state runs until a counter reaches a state-specific limit — WAIT_INDEX for HOLD, FIND_INDEX for FIND_PATTERN, offset for ADD_OFFSET, MSG_LENGTH for RECORD, SKIP_INDEX for SKIP. Document these as notes on each state node.

03.

Model the init transition

Start from [*] and arrow into HOLD — this represents system initialization and makes the entry point explicit.

04.

Use a choice node for branching logic

After FIND_PATTERN detects a candidate pattern, there are two possible next states depending on whether an offset correction is needed. A <<choice>> node makes this branch readable without cluttering the state definitions.

05.

Close the decimation loop

RECORD → SKIP → RECORD is the core cycle. The counter inside each state determines how many bytes get captured vs. discarded, implementing the 1-in-M message decimation.

06.

Add the buffer-full exit

SKIP → HOLD fires when interm_buffer_counter > PROCESS_BUFFER_SIZE — the system has filled its output buffer and resets to wait for the next read cycle. Model this as a guarded transition with the condition labeled on the arrow.

07.

Use notes to carry implementation details

State diagrams communicate structure, not values. Use note left of and note right of to attach the specific limit constants to each state without cluttering the transition arrows.

Share with others

Project Timeline Gantt Chart

Track project tasks, dependencies, and timelines in one visual schedule. This template shows what needs to happen when, helping teams coordinate work, spot scheduling conflicts, and keep stakeholders informed on progress. Essential for project planning, resource allocation, sprint planning, or communicating delivery timelines to clients.

Mermaid

P2P Process Flow (detailed)

Map the full Procure-to-Pay lifecycle across four swimlanes: from purchase requisition through goods receipt and supplier invoice to final payment. Built for finance and operations teams who need to document, audit, or onboard staff to procurement workflows. Each decision point and approval gate is explicit, so there's no ambiguity about who owns what.

Aditya Kumar, Finance Analyst

System State Diagram

Map how systems, objects, or processes transition between different states based on events or conditions. This template shows all possible states and the triggers that cause transitions — helping teams design robust behavior, catch edge cases, and document how things should work. Essential for software design, workflow automation, or explaining any system that changes over time.

Mermaid

System Timeline Diagram

Track events and processes over time with a visual timeline. This diagram helps teams see sequences, responsibilities, and parallel activities clearly for planning, reporting, or retrospectives.

State-Machine Based Decimation Filter for LiDAR UART Streaming

How to create a State-Machine Based Decimation Filter for LiDAR UART Streaming

Define your states before your transitions

List every mode the system can be in: HOLD (idle), FIND_PATTERN (sync detection), ADD_OFFSET (byte alignment), RECORD (capture), SKIP (discard). Each state has exactly one job.

Assign a limit to each state

Every state runs until a counter reaches a state-specific limit — WAIT_INDEX for HOLD, FIND_INDEX for FIND_PATTERN, offset for ADD_OFFSET, MSG_LENGTH for RECORD, SKIP_INDEX for SKIP. Document these as notes on each state node.

Model the init transition

Start from [*] and arrow into HOLD — this represents system initialization and makes the entry point explicit.

Use a choice node for branching logic

After FIND_PATTERN detects a candidate pattern, there are two possible next states depending on whether an offset correction is needed. A <<choice>> node makes this branch readable without cluttering the state definitions.

Close the decimation loop

RECORD → SKIP → RECORD is the core cycle. The counter inside each state determines how many bytes get captured vs. discarded, implementing the 1-in-M message decimation.

Add the buffer-full exit

SKIP → HOLD fires when interm_buffer_counter > PROCESS_BUFFER_SIZE — the system has filled its output buffer and resets to wait for the next read cycle. Model this as a guarded transition with the condition labeled on the arrow.

Use notes to carry implementation details

State diagrams communicate structure, not values. Use note left of and note right of to attach the specific limit constants to each state without cluttering the transition arrows.

Share with others

Tags

You might also like

Project Timeline Gantt Chart

Mermaid

P2P Process Flow (detailed)

Aditya Kumar, Finance Analyst

System State Diagram

Mermaid

System Timeline Diagram

Track events and processes over time with a visual timeline. This diagram helps teams see sequences, responsibilities, and parallel activities clearly for planning, reporting, or retrospectives.

Mermaid