Future Phases: BLE GATT Server Integration¶

Power Management Compatibility Notes¶

Date: November 4, 2025
Status: Planning for Post-Phase 4
Context: BLE GATT server role for remote control/monitoring

Overview¶

After completing Phase 0.4 (Full JPL Compliance), the next major feature will be BLE GATT server functionality. This document outlines power management considerations for BLE integration.

BLE + Light Sleep Compatibility ✅¶

Good news: ESP32-C6 supports BLE connections during light sleep!

How It Works:¶

// Phase 2/3 light sleep (current)
vTaskDelay(pdMS_TO_TICKS(375));  // Auto light sleep
// → CPU sleeps, BLE would disconnect ❌

// BLE-compatible light sleep (future)
CONFIG_PM_ENABLE=y                          // Power management
CONFIG_BT_ENABLED=y                         // BLE stack
CONFIG_BTDM_CTRL_MODE_BLE_ONLY=y           // BLE only (no classic)
CONFIG_PM_POWER_DOWN_CPU_IN_LIGHT_SLEEP=y  // CPU can sleep
CONFIG_BT_SLEEP_ENABLE=y                   // BLE light sleep mode
CONFIG_BTDM_MODEM_SLEEP_MODE_ORIG=y        // Modem sleep during idle

// Then in code:
vTaskDelay(pdMS_TO_TICKS(375));
// → CPU enters light sleep
// → BLE modem stays active (low power mode)
// → BLE connections maintained ✅
// → Wakes on BLE events OR timer

Power Consumption with BLE:¶

State	Current (No BLE)	Current (with BLE)	Notes
Motor active	80mA	85mA	+5mA for BLE radio
Coast (light sleep)	2-5mA	8-12mA	BLE modem active
Advertising only	N/A	10-15mA	No connections
Connected idle	N/A	8-12mA	Connection maintained
Deep sleep	<1mA	N/A	❌ BLE disconnects

Key Point: Light sleep is perfect for BLE. Deep sleep disconnects!

Architecture Changes Needed¶

Phase ⅔ (Current): Device-Only Operation¶

┌─────────────────────────────────────┐
│         EMDR Pulser Device          │
├─────────────────────────────────────┤
│ Button Control (GPIO1)              │
│  → Mode changes                     │
│  → Emergency shutdown               │
│                                     │
│ Motor Task                          │
│  → 4 modes (bilateral stimulation) │
│  → Light sleep during coast         │
│                                     │
│ Battery Task                        │
│  → Voltage monitoring               │
│  → LVO protection                   │
└─────────────────────────────────────┘

Future: BLE GATT Server Integration¶

┌─────────────────────────────────────┐    ┌──────────────────┐
│         EMDR Pulser Device          │◄──►│  Phone/Tablet    │
│           (GATT Server)             │    │  (GATT Client)   │
├─────────────────────────────────────┤    ├──────────────────┤
│ BLE Task (NEW)                      │    │ Custom App       │
│  → GATT server                      │    │  → Mode select   │
│  → Characteristics:                 │    │  → Session start │
│    • Mode (R/W)                     │    │  → Battery level │
│    • Session control (W)            │    │  → Statistics    │
│    • Battery level (R/Notify)       │    └──────────────────┘
│    • Motor status (R/Notify)        │
│                                     │
│ Button Control (GPIO1)              │
│  → Fallback if BLE disconnected     │
│  → Emergency shutdown (always)      │
│                                     │
│ Motor Task                          │
│  → Receives commands from:          │
│    • BLE task queue (remote)        │
│    • Button task queue (local)      │
│  → Light sleep during coast ✅      │
│                                     │
│ Battery Task                        │
│  → Sends notifications to BLE       │
│  → LVO protection                   │
└─────────────────────────────────────┘

Configuration Changes for BLE¶

Additional sdkconfig Settings:¶

#
# Bluetooth
#
CONFIG_BT_ENABLED=y
CONFIG_BT_BLE_ENABLED=y
CONFIG_BTDM_CTRL_MODE_BLE_ONLY=y       # BLE only (no BR/EDR)
CONFIG_BT_NIMBLE_ENABLED=y              # Use NimBLE stack

#
# NimBLE Options
#
CONFIG_BT_NIMBLE_ROLE_PERIPHERAL=y      # GATT server role
CONFIG_BT_NIMBLE_ROLE_BROADCASTER=y     # Advertising
CONFIG_BT_NIMBLE_MAX_CONNECTIONS=1      # Single connection

#
# BLE Power Management
#
CONFIG_BT_SLEEP_ENABLE=y                # Enable BLE sleep
CONFIG_BTDM_MODEM_SLEEP_MODE_ORIG=y    # Modem sleep during idle
CONFIG_PM_ENABLE=y                      # Required for BLE sleep
CONFIG_FREERTOS_USE_TICKLESS_IDLE=y    # Light sleep

#
# BLE Security (Optional)
#
CONFIG_BT_NIMBLE_SM_LEGACY=y            # Pairing support
CONFIG_BT_NIMBLE_SM_SC=y                # Secure connections

platformio.ini Changes:¶

[env:single_device_ble_gatt]
extends = env:single_device_battery_bemf_queued_test

build_flags = 
    ${env:single_device_battery_bemf_queued_test.build_flags}
    -DBLE_GATT_SERVER=1                # Enable BLE features
    -DBLE_DEVICE_NAME="EMDR_Pulser"   # BLE advertising name

GATT Service Design (Draft)¶

EMDR Therapy Service (Primary)¶

UUID: 0000FE00-0000-1000-8000-00805F9B34FB (custom service)

Characteristics:¶

Mode Control (Read/Write)
UUID: 0000FE01-...-34FB
Type: uint8
Values: 0=Mode1, 1=Mode2, 2=Mode3, 3=Mode4
Permissions: Read, Write
Action: Sends message to motor task queue
Session Control (Write)
UUID: 0000FE02-...-34FB
Type: uint8
Values: 0=Stop, 1=Start, 2=Pause
Permissions: Write
Action: Controls session state
Battery Level (Read/Notify)
UUID: 0000FE03-...-34FB
Type: uint8
Values: 0-100 (percentage)
Permissions: Read, Notify
Update: Every 10 seconds (from battery task)
Motor Status (Read/Notify)
UUID: 0000FE04-...-34FB
Type: uint8
Values: 0=Stopped, 1=Forward, 2=Reverse, 3=Coast
Permissions: Read, Notify
Update: On state change
Session Time Remaining (Read/Notify)
UUID: 0000FE05-...-34FB
Type: uint16
Values: Seconds remaining
Permissions: Read, Notify
Update: Every second

Battery Service (Standard)¶

UUID: 0x180F (org.bluetooth.service.battery_service)

Characteristics:¶

Battery Level (Read/Notify)
UUID: 0x2A19 (org.bluetooth.characteristic.battery_level)
Type: uint8
Values: 0-100 (percentage)
Standard battery service

Message Queue Architecture (BLE Integration)¶

New Queue: BLE → Motor¶

// Add new queue
static QueueHandle_t ble_to_motor_queue = NULL;

// In ble_task:
void handle_mode_write(uint8_t new_mode) {
    task_message_t msg = {
        .type = MSG_MODE_CHANGE,
        .data.new_mode = new_mode
    };
    xQueueSend(ble_to_motor_queue, &msg, pdMS_TO_TICKS(100));
}

// In motor_task (modified):
while (session_active) {
    // Check ALL queues (priority order)
    task_message_t msg;

    // 1. Button (highest priority - local control)
    if (xQueueReceive(button_to_motor_queue, &msg, 0) == pdPASS) {
        handle_motor_command(&msg);
    }

    // 2. BLE (medium priority - remote control)
    else if (xQueueReceive(ble_to_motor_queue, &msg, 0) == pdPASS) {
        handle_motor_command(&msg);
    }

    // 3. Battery (lowest priority - warnings)
    else if (xQueueReceive(battery_to_motor_queue, &msg, 0) == pdPASS) {
        handle_battery_warning(&msg);
    }

    // Run motor cycle...
}

New Queue: Motor → BLE (Status Updates)¶

// Add new queue
static QueueHandle_t motor_to_ble_queue = NULL;

// In motor_task:
void update_motor_state(motor_state_t state) {
    ble_notification_t notif = {
        .type = NOTIF_MOTOR_STATUS,
        .data.motor_state = state
    };
    xQueueSend(motor_to_ble_queue, &notif, 0);  // Non-blocking
}

// In ble_task:
void ble_task(void *pvParameters) {
    while (1) {
        ble_notification_t notif;
        if (xQueueReceive(motor_to_ble_queue, &notif, pdMS_TO_TICKS(100)) == pdPASS) {
            // Send BLE notification to connected client
            ble_gatts_notify(notif.characteristic, notif.data);
        }
    }
}

Power Budget with BLE¶

Current (Phase 2 - No BLE):¶

Component	Active	Light Sleep	Notes
ESP32-C6 CPU	60mA	2mA	Tickless idle
Motor (avg)	10mA	0mA	25% duty cycle
Peripherals	3mA	0.5mA	ADC, LEDC, etc.
Total	73mA	2.5mA
Average (Mode 2)	25mA		75% idle time

Future (with BLE):¶

Component	Active	Light Sleep	Notes
ESP32-C6 CPU	60mA	2mA	Tickless idle
BLE Radio	5mA	6mA	Always on for connections
Motor (avg)	10mA	0mA	25% duty cycle
Peripherals	3mA	0.5mA	ADC, LEDC, etc.
Total	78mA	8.5mA
Average (Mode 2)	32mA		+7mA vs no BLE

Battery Life Impact:¶

Configuration	Mode 2 Current	Battery Life (dual 320mAh - 640mAh total)	vs Phase 2
Phase 2 (No BLE)	25mA	~50 minutes	Baseline
Future (with BLE)	32mA	~40 minutes	-20%

Tradeoff: Remote control costs ~10 minutes of battery life, but adds significant UX value.

Implementation Phases¶

Phase 5: Basic BLE (After Phase 4)¶

Effort: 1-2 weeks
Goal: Minimal BLE GATT server

Features: - ✅ BLE advertising - ✅ Single connection - ✅ Mode control characteristic (R/W) - ✅ Battery level characteristic (R/Notify) - ✅ Light sleep with BLE maintained - ✅ Button control still works (fallback)

Phase 6: Advanced BLE (Optional)¶

Effort: 2-3 weeks
Goal: Full remote control and monitoring

Features: - ✅ Session control (start/stop/pause) - ✅ Motor status notifications - ✅ Session timer - ✅ Statistics (total sessions, battery cycles) - ✅ BLE security (pairing, encryption) - ✅ Firmware update over BLE (OTA)

Testing Strategy¶

BLE + Light Sleep Verification:¶

Connection Stability:
Connect phone to EMDR pulser via BLE
Start motor (enters light sleep during coast)
Verify BLE connection maintained for 20 minutes
Expected: No disconnections
Command Responsiveness:
Connect via BLE
Send mode change command during coast (device in light sleep)
Measure response latency
Expected: <100ms wake + command processing
Power Consumption:
Measure current with BLE connected vs disconnected
Verify BLE sleep mode active during coast
Expected: ~6-8mA additional (BLE modem)
Notification Throughput:
Subscribe to battery + motor status notifications
Run 20-minute session
Verify all notifications received
Expected: 100% delivery rate

Compatibility Matrix¶

Feature	Deep Sleep	Light Sleep (No BLE)	Light Sleep (BLE)
Motor control	✅	✅	✅
Button wake	✅	✅	✅
Battery monitoring	✅	✅	✅
Power savings	⭐⭐⭐⭐⭐	⭐⭐⭐⭐	⭐⭐⭐
BLE connections	❌	❌	✅
Remote control	❌	❌	✅
Use case	Standalone only	Standalone only	Remote + Standalone

Security Considerations¶

BLE Security Features:¶

Pairing (Optional):
Numeric comparison (most secure)
Prevents unauthorized control
Configurable: Open vs Paired
Encryption:
Link-layer encryption
Protects command/data transmission
Standard BLE security
Access Control:
Emergency shutdown always via button
Critical safety functions not BLE-controlled
BLE for convenience only

Recommended Security Policy:¶

// Default: Open (no pairing required)
// User can enable pairing via button sequence
// Critical functions (emergency stop) always via button

Conclusion¶

BLE + Light Sleep = Perfect Match ✅

Key Points: - Light sleep maintains BLE connections (deep sleep doesn't) - Power cost: ~7mA additional for BLE - Battery life: ~40 minutes (vs 50 without BLE) - User experience: Significantly improved with remote control - Architecture: Message queues already support BLE integration - Implementation: Straightforward after Phase 4 complete

Phase ⅔ light sleep architecture is BLE-ready!

References¶

ESP32-C6 BLE Power Management: https://docs.espressif.com/projects/esp-idf/en/v5.5/esp32c6/api-guides/low-power-mode.html
NimBLE Stack: https://docs.espressif.com/projects/esp-idf/en/v5.5/esp32c6/api-reference/bluetooth/nimble/index.html
GATT Services: https://www.bluetooth.com/specifications/gatt/
ESP32 BLE Examples: https://github.com/espressif/esp-idf/tree/v5.5/examples/bluetooth/nimble

Next Steps: Complete Phase 2-4, then implement BLE in Phase 5! 🚀