LE Controller

Overview

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

Architecture Overview

Scheduling

Ticker

Upper Link Layer and Lower Link Layer

Scheduling Variants

ULL and LLL Timing

Event Handling

Scheduling Closely Spaced Events

Aborting Active Event

Cancelling Pending Event

Pre-emption of Active Event

Data Flow

Transmit Data Flow

Receive Data Flow

Execution Priorities

• 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.

Link Layer Control Procedures

Following is a brief fly in on the main concepts in the implementation of control procedures handling in ULL.

Three main execution contexts

• HCI/LLCP API

  • Miscellaneous procedure initiation API

  • From ull_llcp.c::ull_cp_<proc>() for initiating local procedures

  • Interface with running procedures, local and remote

• lll_prepare context to drive ull_cp_run()

  • LLCP main state machine entry/tick’er

  • From ull_peripheral.c/ull_central.c::ticker_cb via ull_conn_llcp()

• rx_demux context to drive ull_cp_tx_ack() and ull_cp_rx()

  • LLCP tx ack handling and PDU reception

  • From ull_conn.c::ull_conn_rx()

  • Handles passing PDUs into running procedures as well as possibly initiating remote procedures

Data structures and PDU helpers

• struct llcp_struct

  • Main LLCP data store

  • Defined in ull_conn_types.h and declared as part of struct ll_conn

  • Holds local and remote procedure request queues as well as conn specific LLCP data

  • Basic conn-level abstraction

• struct proc_ctx

  • General procedure context data, contains miscellaneous procedure data and state as well as sys_snode_t for queueing

  • Defined in ull_llcp_internal.h, declared/instantiated through ull_llcp.c::create_procedure()

  • Also holds node references used in tx_ack as well as rx_node retention mechanisms

• struct llcp_mem_pool

  • Mem pool used to implement procedure contexts resource - instantiated in both a local and a remote version

  • Used through ull_llcp.c::create_procedure()

• Miscellaneous pdu gymnastics

  • Encoding and decoding of control pdus done by ull_llcp_pdu.c::llcp_pdu_encode/decode_<PDU>()

  • Miscellaneous pdu validation handled by ull_llcp.c::pdu_validate_<PDU>() via ull_llcp.c::pdu_is_valid()

LLCP local and remote request/procedure state machines

• ull_llcp_local.c

  • State machine handling local initiated procedures

  • Naming concept: lr _<…> => local request machine

  • Local procedure queue handling

  • Local run/rx/tx_ack switch

• ull_llcp_remote.c

  • Remote versions of the above

  • Naming concept: rr_<…> => remote request machine

  • Also handling of remote procedure initiation by llcp_rx_new()

  • Miscellaneous procedure collision handling (in rr_st_idle())

• ull_llcp_common/conn_upd/phy/enc/cc/chmu.c

  • Individual procedure implementations (ull_llcp_common.c collects the simpler ones)

  • Naming concept: lp_<…> => local initiated procedure, rp_<…> => remote initiated procedure

  • Handling of procedure flow from init (possibly through instant) to completion and host notification if applicable

Miscellaneous concepts

• Procedure collision handling

  • See BT spec for explanation

  • Basically some procedures can exist in parallel but some can’t - for instance only one instant based at a time

  • Spec states rules for how to handle/resolve collisions when they happen

• Termination handling

  • Specific rules apply re. how termination is handled.

  • Since we have resource handling re. procedure contexts and terminate must always be available this is handled as a special case

  • Note also - there are miscellaneous cases where connection termination is triggered on invalid peer behavior

• New remote procedure handling

  • Table new_proc_lut[] maps LLCP PDUs to procedures/roles used in llcp_rr_new()

  • Note - for any given connection, there can only ever be ONE remote procedure in the remote procedure queue

• Miscellaneous minors

  • pause/resume concepts - there are two (see spec for details)

  • procedure execution can be paused by the encryption procedure

  • data TX can be paused by PHY, DLE and ENC procedure

  • RX node retention - ensures no waiting for allocation of RX node when needed for notification

Miscellaneous unit test concepts

• Individual ZTEST unit test for each procedure

  • zephyr/tests/bluetooth/controller/ctrl_<proc>

• Rx node handling is mocked

  • Different configs are handled by separate conf files (see ctrl_conn_update for example)

  • ZTEST(periph_rem_no_param_req, test_conn_update_periph_rem_accept_no_param_req)

• Emulated versions of rx_demux/prepare context used in unit tests - testing ONLY procedure PDU flow

  • event_prepare()/event_done() helpers emulating LLL prepare/done flow

  • lt_rx()/lt_tx() ‘lower tester’ emulation of rx/tx

  • ut_rx_node() ‘upper tester’ emulation of notification flow handling

  • Bunch of helpers to generate and parse PDUs, as well as miscellaneous mocked ull_stuff()

Lower Link Layer

LLL Execution

LLL Resume

Bare metal utilities

Memory FIFO and Memory Queue

Mayfly

• 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

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)

[0]

CONFIG_BT_CTLR_TIFS_HW =n

[1] (1,2)

CONFIG_BT_CTLR_SW_SWITCH_SINGLE_TIMER =y

[2]

When not using pre-defined PPI channels

[3] (1,2)

For software-based tIFS switching

[4] (1,2)

Drivers that use nRFx interfaces

[5] (1,2)

For nRF53x Series