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//! Link-Layer. //! //! Note that a hardware BLE radio will already implement a few aspects of the link layer (such as //! CRC calculation, preamble generation, etc.). Consider this module to be a construction kit for //! BLE Link-Layers: Take whatever your hardware can do, supplement it with a few condiments from //! this module, and you get a (hopefully) working Link-Layer. //! //! Refer to the official *Link Layer Specification* for details and more graphics and tables. //! //! # Packet Format //! //! All following graphics are based on the Bluetooth specification. If a field is marked with `-`, //! it should be set to 0 when sending such a packet, and ignored when receiving it (the spec calls //! these "RFU" = Reserved for Future Use). //! //! All values are transmitted in little-endian bit order unless otherwise noted. All fields in //! graphics are ordered starting with the field transmitted first (LSB). //! //! The following graphic illustrates the raw in-air packet format. The packet transfers a PDU whose //! format depends on whether it is sent on an *advertising channel* or a *data channel*. //! //! ```notrust //! LSB MSB //! +-----------+----------------+---------------+------------+ //! | Preamble | Access Address | PDU | CRC | //! | (1 octet) | (4 octets) | (2-39 octets) | (3 octets) | //! +-----------+----------------+---------------+------------+ //! \---------------/ ^ //! | | //! +--------------+ //! CRC is calculated //! over the PDU //! //! \----------------------------/ //! Data Whitening is //! applied to PDU and CRC //! ``` //! //! The 24-bit CRC value is transmitted MSb first. Length of the PDU depends on the kind of PDU //! (advertising or data channel). //! //! ## Advertising Channel PDU //! //! Each advertising channel PDU consists of a 16-bit header and a variably-sized payload, the //! length of which is stored in a header field. //! //! ```notrust //! LSB MSB //! +-------------+---------------------------------+ //! | Header | Payload | //! | (16 bits) | (length stored in header) | //! +-------------+---------------------------------+ //! ``` //! //! The header looks like this: //! //! ```notrust //! LSB MSB //! +------------+------------+---------+---------+--------------+------------+ //! | PDU Type | - | TxAdd | RxAdd | Length | - | //! | (4 bits) | (2 bits) | (1 bit) | (1 bit) | (6 bits) | (2 bits) | //! +------------+------------+---------+---------+--------------+------------+ //! ``` //! //! The `TxAdd` and `RxAdd` field are only used for some payloads, for all others, they should be //! set to 0. //! //! Length may be in range 6 to 36 (inclusive). //! //! The data in `Payload` depends on the PDU Type. Refer to the spec or [`advertising::PduType`] for //! details. //! //! [`advertising::PduType`]: advertising/enum.PduType.html //! //! ## Data Channel PDU //! //! A data channel PDU also contains a 16-bit header (but with a different layout) and a //! variably-sized payload. //! //! If the connection is encrypted and the payload contains at least 1 octet, a Message Integrity //! Check (MIC) is appended at the end. //! //! ```notrust //! LSB MSB //! +-----------+----------------------+ - - - - - + //! | Header | Payload | MIC | //! | (16 bits) | (0..=27 octets) | (32 bits) | //! +-----------+----------------------+ - - - - - + //! ``` //! //! Layout (in Bluetooth 4.2): //! //! ```notrust //! LSB MSB //! +----------+---------+---------+---------+------------+--------------+ //! | LLID | NESN | SN | MD | - | Length | //! | (2 bits) | (1 bit) | (1 bit) | (1 bit) | (3 bits) | (8 bits) | //! +----------+---------+---------+---------+------------+--------------+ //! ``` //! //! Payload format depends on the value of the 2-bit `LLID` field: //! //! * `0b00`: Reserved value. //! * `0b01`: LL Data PDU Continuation fragment or empty PDU. //! * `0b10`: LL Data PDU Start of L2CAP message (or complete message if no fragmentation //! necessary). //! * `0b11`: LL Control PDU. //! //! The `NESN` field specifies the **N**ext **E**xpected **S**equence **N**umber. The `SN` field //! specifies the **S**equence **N**umber of this PDU. //! //! The `MD` field specifies that the device sending the packet has more data to send during this //! *connection event*. When both slave and master send a packet with the `MD` bit set to 0, the //! connection event ends. //! //! The `Length` field specifies the length of payload **and `MIC`**. For Bluetooth versions <4.2, //! its maximum value is 31, resulting in a 27 octet Payload (the maximum) and a 32-bit `MIC`. 4.2 //! added the possibility of larger packets. pub mod ad_structure; pub mod advertising; mod comp_id; mod connection; pub mod data; mod device_address; mod features; pub mod filter; pub mod queue; mod responder; mod seq_num; pub use self::comp_id::*; pub use self::device_address::*; pub use self::features::*; pub use self::responder::*; use { self::{ ad_structure::AdStructure, advertising::{Pdu, PduBuf}, connection::Connection, queue::{Consumer, Producer}, seq_num::SeqNum, }, crate::{ bytes::ByteReader, crc::ble_crc24, phy::{AdvertisingChannel, DataChannel, Radio}, time::{Duration, Instant, Timer}, utils::HexSlice, Error, }, byteorder::{ByteOrder, LittleEndian}, core::ops::Range, }; /// The CRC polynomial to use for CRC24 generation. /// /// If your radio has hardware support for CRC generation, you may use (parts of) this value to /// configure it (if necessary). The CRC should be computed only over the PDU. Also note that the /// CRC, unlike every other field, is transmitted MSb first. /// /// Counting from the least-significant bit (bit 0), bit `k` in this value is set if the term `x^k` /// occurs in the CRC polynomial. This includes bit 24, which is usually not explicitly specified. /// /// Written out, the polynomial is: /// /// `x^24 + x^10 + x^9 + x^6 + x^4 + x^3 + x + 1` pub const CRC_POLY: u32 = 0b00000001_00000000_00000110_01011011; /// Max. PDU payload size in Bytes (for both advertising and data channels). pub const MAX_PAYLOAD_SIZE: usize = 255; /// Max. PDU size in octets (header + payload). pub const MAX_PDU_SIZE: usize = MAX_PAYLOAD_SIZE + 2; // data & adv. have a 16-bit header /// Max. total Link-Layer packet size in octets. pub const MAX_PACKET_SIZE: usize = 1 /* preamble */ + 4 /* access addr */ + MAX_PDU_SIZE + 3 /* crc */; /// Defines types that provide platform-dependent functionality. pub trait HardwareInterface { /// A timesource with microsecond accuracy. type Timer: Timer; /// The BLE packet transmitter. type Tx: Transmitter; } /// Link-Layer state machine, according to the Bluetooth spec. enum State<HW: HardwareInterface> { /// Radio silence: Not listening, not transmitting anything. Standby, /// Device is advertising and wants to establish a connection. Advertising { /// Advertising interval. // TODO: check spec for allowed/recommended values and check for them next_adv: Instant, interval: Duration, /// Precomputed PDU payload to copy into the transmitter's buffer. pdu: advertising::PduBuf, /// Next advertising channel to use for a message. // FIXME: spec check; no idea what order or change delay channel: AdvertisingChannel, data_queues: Option<(Consumer, Producer)>, }, /// Connected with another device. Connection(Connection<HW>), } /// Implementation of the real-time BLE Link-Layer logic. /// /// Users of this struct must provide an interface to the platform's hardware by implementing /// `HardwareInterface`. pub struct LinkLayer<HW: HardwareInterface> { dev_addr: DeviceAddress, state: State<HW>, timer: HW::Timer, } impl<HW: HardwareInterface> LinkLayer<HW> { /// Creates a new Link-Layer. /// /// # Parameters /// /// * **`dev_addr`**: The device address to broadcast as. /// * **`timer`**: A `Timer` implementation. /// * **`tx`**: Input queue of packets to transmit when connected. /// * **`rx`**: Output queue of received packets when connected. pub fn new(dev_addr: DeviceAddress, timer: HW::Timer) -> Self { trace!("new LinkLayer, dev={:?}", dev_addr); Self { dev_addr, state: State::Standby, timer, } } /// Returns a reference to the timer instance used by the Link-Layer. pub fn timer(&mut self) -> &mut HW::Timer { &mut self.timer } /// Starts advertising this device, optionally sending data along with the advertising PDU. pub fn start_advertise( &mut self, interval: Duration, data: &[AdStructure], transmitter: &mut HW::Tx, tx: Consumer, rx: Producer, ) -> Result<NextUpdate, Error> { // TODO tear down existing connection? let pdu = PduBuf::discoverable(self.dev_addr, data)?; debug!("start_advertise: adv_data = {:?}", data); debug!("start_advertise: PDU = {:?}", pdu); self.state = State::Advertising { next_adv: self.timer().now(), interval, pdu, channel: AdvertisingChannel::first(), data_queues: Some((tx, rx)), }; Ok(self.update(transmitter).next_update) } /// Process an incoming packet from an advertising channel. /// /// The access address of the packet must be `ADVERTISING_ADDRESS`. /// /// # Parameters /// /// * **`rx_end`**: A timestamp indicating when the packet was fully received. /// * **`tx`**: A packet transmitter. /// * **`header`**: The header of the received packet. /// * **`payload`**: The packet payload following the header. /// * **`crc_ok`**: Whether the packet's CRC is correct. pub fn process_adv_packet( &mut self, rx_end: Instant, tx: &mut HW::Tx, header: advertising::Header, payload: &[u8], crc_ok: bool, ) -> Cmd { let pdu = advertising::Pdu::from_header_and_payload(header, &mut ByteReader::new(payload)); if let Ok(pdu) = pdu { if let State::Advertising { channel, data_queues, .. } = &mut self.state { if crc_ok && pdu.receiver() == Some(&self.dev_addr) { // Got a packet addressed at us, can be a scan or connect request match pdu { Pdu::ScanRequest { .. } => { let scan_data = &[]; // TODO make this configurable let response = PduBuf::scan_response(self.dev_addr, scan_data).unwrap(); tx.transmit_advertising(response.header(), *channel); // Log after responding to meet timing debug!("-> SCAN RESP: {:?}", response); } Pdu::ConnectRequest { lldata, .. } => { trace!("ADV<- CONN! {:?}", pdu); let (tx, rx) = data_queues.take().unwrap(); let (conn, cmd) = Connection::create(&lldata, rx_end, tx, rx); self.state = State::Connection(conn); return cmd; } _ => {} } } } } trace!( "ADV<- {}{:?}, {:?}\n{:?}\n", if crc_ok { "" } else { "BADCRC " }, header, HexSlice(payload), pdu, ); match self.state { State::Standby => unreachable!("standby, can't receive packets"), State::Connection { .. } => unimplemented!(), State::Advertising { channel, .. } => { Cmd { radio: RadioCmd::ListenAdvertising { channel }, // no change next_update: NextUpdate::Keep, } } } } /// Process an incoming data channel packet. pub fn process_data_packet( &mut self, rx_end: Instant, tx: &mut HW::Tx, header: data::Header, payload: &[u8], crc_ok: bool, ) -> Cmd { if let State::Connection(conn) = &mut self.state { match conn.process_data_packet(rx_end, tx, &mut self.timer, header, payload, crc_ok) { Ok(cmd) => cmd, Err(()) => { debug!("connection ended, standby"); self.state = State::Standby; Cmd { next_update: NextUpdate::Disable, radio: RadioCmd::Off, } } } } else { unreachable!("received data channel PDU while not in connected state"); } } /// Update the Link-Layer state. /// /// This should be called in regular intervals, independent of whether packets were received and /// processed. /// /// # Parameters /// /// * `tx`: A `Transmitter` for sending packets. /// * `elapsed`: Time since the last `update` call or creation of this `LinkLayer`. pub fn update(&mut self, tx: &mut HW::Tx) -> Cmd { match &mut self.state { State::Advertising { next_adv, interval, pdu, channel, .. } => { *channel = channel.cycle(); let payload = pdu.payload(); let buf = tx.tx_payload_buf(); buf[..payload.len()].copy_from_slice(payload); // FIXME According to the spec, this has to broadcast on all advertising channels tx.transmit_advertising(pdu.header(), *channel); *next_adv += *interval; Cmd { radio: RadioCmd::ListenAdvertising { channel: *channel }, next_update: NextUpdate::At(*next_adv), } } State::Connection(conn) => match conn.timer_update(&mut self.timer) { Ok(cmd) => cmd, Err(()) => { debug!("connection ended (timer), standby"); self.state = State::Standby; Cmd { next_update: NextUpdate::Disable, radio: RadioCmd::Off, } } }, State::Standby => unreachable!("LL in standby received timer event"), } } pub fn is_advertising(&self) -> bool { if let State::Advertising { .. } = self.state { true } else { false } } } /// Command returned by the Link-Layer to the user. /// /// Specifies how the radio should be configured and when/if to call `LinkLayer::update` again. #[must_use] #[derive(Debug, Clone)] pub struct Cmd { /// Radio configuration request. pub radio: RadioCmd, /// Time until `LinkLayer::update` should be called. /// /// If this is `None`, `update` doesn't need to be called because the Link-Layer is in Standby /// state. pub next_update: NextUpdate, } /// Specifies when the Link Layer's `update` method should be called the next time. #[derive(Debug, Clone)] pub enum NextUpdate { /// Disable timer and do not call `update`. Disable, /// Keep the previously configured time. Keep, /// Call `update` at the given `Instant`. /// /// If `Instant` is in the past, this is a bug and the implementation may panic. At(Instant), } /// Specifies if and how the radio should listen for transmissions. /// /// Returned by the Link-Layer update and processing methods to reconfigure the radio as needed. #[derive(Debug, Clone)] pub enum RadioCmd { /// Turn the radio off and don't call `LinkLayer::process_*` methods. /// /// `LinkLayer::update` must still be called according to `Cmd`'s `next_update` field. Off, /// Listen on an advertising channel. If a packet is received, pass it to /// `LinkLayer::process_adv_packet`. ListenAdvertising { /// The advertising channel to listen on. channel: AdvertisingChannel, }, /// Listen on a data channel. If a matching packet is received, pass it to /// `LinkLayer::process_data_packet`. ListenData { /// The data channel to listen on. channel: DataChannel, /// The Access Address to listen for. /// /// Packets with a different Access Address must not be passed to the Link-Layer. You may be /// able to use your Radio's hardware address matching for this. access_address: u32, /// Initialization value of the CRC-24 calculation. /// /// Only the least significant 24 bits are relevant. crc_init: u32, }, } /// Trait for Link Layer packet transmission. /// /// The specifics of sending a Link-Layer packet depend on the underlying hardware. The `link` /// module provides building blocks that enable implementations without any BLE hardware support, /// just a compatible radio is needed. pub trait Transmitter { /// Get a reference to the Transmitter's PDU payload buffer. /// /// The buffer must hold at least 37 Bytes, as that is the maximum length of advertising channel /// payloads. While data channel payloads can be up to 251 Bytes in length (resulting in a /// "length" field of 255 with the MIC), devices are allowed to use smaller buffers and report /// the supported payload length. /// /// Both advertising and data channel packets also use an additional 2-Byte header preceding /// this payload. /// /// This buffer must not be changed. The BLE stack relies on the buffer to retain its old /// contents after transmitting a packet. A separate buffer must be used for received packets. fn tx_payload_buf(&mut self) -> &mut [u8]; /// Transmit an Advertising Channel PDU. /// /// For Advertising Channel PDUs, the CRC initialization value is always `CRC_PRESET`, and the /// Access Address is always `ADVERTISING_ADDRESS`. /// /// The implementor is expected to send the preamble and access address, and assemble the rest /// of the packet, and must apply data whitening and do the CRC calculation. The inter-frame /// spacing also has to be upheld by the implementor (`T_IFS`). /// /// # Parameters /// /// * `header`: Advertising Channel PDU Header to prepend to the Payload in `payload_buf()`. /// * `channel`: Advertising Channel Index to transmit on. fn transmit_advertising(&mut self, header: advertising::Header, channel: AdvertisingChannel); /// Transmit a Data Channel PDU. /// /// The implementor is expected to send the preamble and assemble the rest of the packet, and /// must apply data whitening and do the CRC calculation. /// /// # Parameters /// /// * `access_address`: The Access Address of the Link-Layer packet. /// * `crc_iv`: CRC calculation initial value (`CRC_PRESET` for advertising channel). /// * `header`: Data Channel PDU Header to be prepended to the Payload in `payload_buf()`. /// * `channel`: Data Channel Index to transmit on. fn transmit_data( &mut self, access_address: u32, crc_iv: u32, header: data::Header, channel: DataChannel, ); } /// A `Transmitter` that lowers Link-Layer packets to raw byte arrays that can be directly /// transmitted over the air, given a suitable radio. /// /// This implements preamble generation, CRC calculation and whitening in software. pub struct RawTransmitter<R: Radio> { tx_buf: [u8; MAX_PACKET_SIZE], radio: R, } // First 5 octets are Preamble and Access Address const PDU_START: usize = 5; const HEADER_RANGE: Range<usize> = PDU_START..PDU_START + 2; const PAYLOAD_RANGE: Range<usize> = PDU_START + 2..PDU_START + MAX_PDU_SIZE; impl<R: Radio> RawTransmitter<R> { pub fn new(radio: R) -> Self { Self { tx_buf: [0; MAX_PACKET_SIZE as usize], radio, } } fn transmit(&mut self, access_address: u32, payload_length: u8, crc_iv: u32, freq: u16) { let preamble = if access_address & 1 == 1 { 0b01010101 } else { 0b10101010 }; self.tx_buf[0] = preamble; LittleEndian::write_u32(&mut self.tx_buf[1..5], access_address); let crc = ble_crc24( &self.tx_buf[PDU_START..PDU_START + 2 + payload_length as usize], crc_iv, ); LittleEndian::write_u24(&mut self.tx_buf[MAX_PACKET_SIZE - 3..], crc); // TODO whitening if true { unimplemented!(); } self.radio.transmit(&mut self.tx_buf, freq); } } impl<R: Radio> Transmitter for RawTransmitter<R> { fn tx_payload_buf(&mut self) -> &mut [u8] { &mut self.tx_buf[PAYLOAD_RANGE] } fn transmit_advertising(&mut self, header: advertising::Header, channel: AdvertisingChannel) { LittleEndian::write_u16(&mut self.tx_buf[HEADER_RANGE], header.to_u16()); self.transmit( advertising::ACCESS_ADDRESS, header.payload_length(), advertising::CRC_PRESET, channel.freq(), ); } fn transmit_data( &mut self, access_address: u32, crc_iv: u32, header: data::Header, channel: DataChannel, ) { LittleEndian::write_u16(&mut self.tx_buf[HEADER_RANGE], header.to_u16()); self.transmit( access_address, header.payload_length(), crc_iv, channel.freq(), ); } }