Bluetooth Low Energy Controller

Overview

../../_images/ctlr_overview.png

  1. HCI

    • Host Controller Interface, Bluetooth standard

    • Provides Zephyr Bluetooth HCI Driver

  2. HAL

    • Hardware Abstraction Layer

    • Vendor Specific, and Zephyr Driver usage

  3. Ticker

    • Soft real time radio/resource scheduling

  4. LL_SW

    • Software-based Link Layer implementation

    • States and roles, control procedures, packet controller

  5. Util

    • Bare metal memory pool management

    • Queues of variable count, lockless usage

    • FIFO of fixed count, lockless usage

    • Mayfly concept based deferred ISR executions

Architecture

Execution Overview

../../_images/ctlr_exec_overview.png

Architecture Overview

../../_images/ctlr_arch_overview.png

Scheduling

../../_images/ctlr_sched.png

Ticker

../../_images/ctlr_sched_ticker.png

Scheduling Variants

../../_images/ctlr_sched_variant.png

ULL and LLL Timing

../../_images/ctlr_sched_ull_lll_timing.png

Event Handling

../../_images/ctlr_sched_event_handling.png

Scheduling Closely Spaced Events

../../_images/ctlr_sched_msc_close_events.png

Aborting Active Event

../../_images/ctlr_sched_msc_event_abort.png

Cancelling Pending Event

../../_images/ctlr_sched_msc_event_cancel.png

Pre-emption of Active Event

../../_images/ctlr_sched_msc_event_preempt.png

Data Flow

Transmit Data Flow

../../_images/ctlr_dataflow_tx.png

Receive Data Flow

../../_images/ctlr_dataflow_rx.png

Execution Priorities

../../_images/ctlr_exec_prio.png

  • Event handle (0, 1) < Event preparation (2, 3) < Event/Rx done (4) < Tx request (5) < Role management (6) < Host (7).

  • LLL is vendor ISR, ULL is Mayfly ISR concept, Host is kernel thread.

Bare metal utilities

Memory FIFO and Memory Queue

../../_images/ctlr_mfifo_memq.png

Mayfly

../../_images/ctlr_mayfly.png

  • Mayfly are multi-instance scalable ISR execution contexts

  • What a Work is to a Thread, Mayfly is to an ISR

  • List of functions executing in ISRs

  • Execution priorities map to IRQ priorities

  • Facilitate cross execution context scheduling

  • Race-to-idle execution

  • Lock-less, bare metal

Legacy Controller

../../_images/ctlr_legacy.png

Bluetooth Low Energy Controller - Vendor Specific Details

Hardware Requirements

Nordic Semiconductor

The Nordic Semiconductor Bluetooth Low Energy Controller implementation requires the following hardware peripherals.

SoC Peripheral Use

Resource

nRF Peripheral

# instances

Zephyr Driver Accessible

Description

Clock

NRF_CLOCK

1

Yes

  • A Low Frequency Clock (LFCLOCK) or sleep clock, for low power consumption between Bluetooth radio events

  • A High Frequency Clock (HFCLOCK) or active clock, for high precision packet timing and software based transceiver state switching with inter-frame space (tIFS) timing inside Bluetooth radio events

RTC [a]

NRF_RTC0

1

No

  • Uses 2 capture/compare registers

Timer

NRF_TIMER0 or NRF_TIMER4 [1], and NRF_TIMER1 [0]

2 or 1 [1]

No

  • 2 instances, one each for packet timing and tIFS software switching, respectively

  • 7 capture/compare registers (3 mandatory, 1 optional for ISR profiling, 4 for single timer tIFS switching) on first instance

  • 4 capture/compare registers for second instance, if single tIFS timer is not used.

PPI [b]

NRF_PPI

21 channels (20 [2]), and 2 channel groups [3]

Yes [4]

  • Used for radio mode switching to achieve tIFS timings, for PA/LNA control

DPPI [c]

NRF_DPPI

20 channels, and 2 channel groups [3]

Yes [4]

  • Used for radio mode switching to achieve tIFS timings, for PA/LNA control

SWI [d]

NRF_SWI4 and NRF_SWI5, or NRF_SWI2 and NRF_SWI3 [5]

2

No

  • 2 instances, for Lower Link Layer and Upper Link Layer Low priority execution context

Radio

NRF_RADIO

1

No

  • 2.4 GHz radio transceiver with multiple radio standards such as 1 Mbps, 2 Mbps and Coded PHY S2/S8 Long Range Bluetooth Low Energy technology

RNG [e]

NRF_RNG

1

Yes

ECB [f]

NRF_ECB

1

No

CBC-CCM [g]

NRF_CCM

1

No

AAR [h]

NRF_AAR

1

No

GPIO [i]

NRF_GPIO

2 GPIO pins for PA and LNA, 1 each

Yes

  • Additionally, 10 Debug GPIO pins (optional)

GPIOTE [j]

NRF_GPIOTE

1

Yes

  • Used for PA/LNA

TEMP [k]

NRF_TEMP

1

Yes

  • For RC sourced LFCLOCK calibration

UART [l]

NRF_UART0

1

Yes

  • For HCI interface in Controller only builds

IPC [m]

NRF_IPC [5]

1

Yes

  • For HCI interface in Controller only builds
[a]

Real Time Counter (RTC)

[b]

Programmable Peripheral Interconnect (PPI)

[c]

Distributed Programmable Peripheral Interconnect (DPPI)

[d]

Software Interrupt (SWI)

[e]

Random Number Generator (RNG)

[f]

AES Electronic Codebook Mode Encryption (ECB)

[g]

Cipher Block Chaining (CBC) - Message Authentication Code with Counter Mode encryption (CCM)

[h]

Accelerated Address Resolver (AAR)

[i]

General Purpose Input Output (GPIO)

[j]

GPIO tasks and events (GPIOTE)

[k]

Temperature sensor (TEMP)

[l]

Universal Asynchronous Receiver Transmitter (UART)

[m]

Interprocess Communication peripheral (IPC)