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Serial Processing & Packet Handling

Serial Processing Overview

Ultra-Fast Interrupt Context

UART Byte Available
↓
Store Single Byte & Exit
(No Frame Processing)

Critical Points:

  • Absolute minimum time in interrupt!
  • Single byte storage only
  • Doesn't care about partial frames
  • Next interrupt will continue frame
  • No processing or validation here

Frame Reception Example:

Interrupt 1: Bytes 1-3
→
Store & Exit
Interrupt 2: Bytes 4-5
→
Store & Exit
Interrupt 3: Bytes 6-8
→
Store & Exit
Frame assembly happens later in main loop

Main Loop Processing

Check Buffer for New Data
↓
Build Packet Buffer
(If new data available)
↓
Validate Packet Type
(Modbus or 0x7E)
↓
Check CRC & Length

Continuous Timeout Check:

Time since last byte greater than 9/baudrate?
Example: greater than 9ms @9600
Clear Buffer
+
Reset Packet Array

Key Points:

  • Runs continuously in main loop
  • Handles packet assembly
  • Validates packet integrity
  • Clears all buffers if timeout occurs
    (No data received for 1 byte period)

Timeout Handling

No UART Activity
→
Clear Buffers
→
Reset State

Important:

  • Timeout based on baud rate period
  • Prevents partial packet processing
  • Ensures clean state for next message

Circular Buffer Operation