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deploy-preemption.md

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Deploy Preemption Protocol

State Machine

MONITOR ATTACHED (reading lines)
        │
    Deploy starts
        │
        ▼
PREEMPTION PHASE
  1. Force-close serial session in SharedSerialManager
  2. All readers receive "preempted" message via WebSocket
  3. auto_reconnect=true → pause (don't raise exception)
  4. auto_reconnect=false → raise MonitorPreemptedException
        │
        ▼
FLASH PHASE
  1. esptool/avrdude acquires exclusive OS serial handle
  2. Flash firmware
  3. Reset device (RTS/DTR sequence)
  4. Release serial handle
        │
        ▼
POST-DEPLOY PHASE
  1. Clear preemption notification
  2. 2-second delay for USB-CDC driver + device reboot
  3. if monitor_after: re-open port, send "reconnected" message
        │
        ▼
MONITOR RESUMED (seamless to client)

Timing

Step Duration Notes
Preemption notify <10ms WebSocket message to all readers
Serial close <100ms Force-close, no graceful flush
Flash (ESP32) 10-30s Depends on firmware size
Flash (AVR) 2-5s Smaller firmware
USB re-enumeration 1-30s Windows worst case; Linux <2s
Boot sequence 1-3s Bootloader + app init
Monitor reconnect <1s Auto-reattach after preemption clear

FastLED Integration

FastLED sets monitor_after=False in deploy requests and manages serial attachment itself:

# Phase 1: Build
conn.build(clean=False, verbose=True)

# Phase 2: Deploy (no auto-monitor)
conn.deploy(port=upload_port, skip_build=True, monitor_after=False)

# Phase 3: Custom RPC attach
with SerialMonitor(port=monitor_port, baud_rate=115200, auto_reconnect=True) as mon:
    await asyncio.sleep(3.0)      # boot_wait
    drain_boot_output()            # clear stale buffer
    mon.write('{"method":"ping","params":[{}],"id":1}\n')
    # Wait for: REMOTE: {"id":1,"result":{...}}

The 3-second boot wait and boot output draining are critical for reliable JSON-RPC communication after flash.