1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197
//! This is a portable minimal implementation of the [System Management Bus (SMBus)][smbus] //! [Packet Error Code][smbus-pec] calculation algorithm intended for use in `no_std`. //! //! SMBus 1.1 and later defines an optional Packet Error Checking mode. When used, an extra byte //! is appended to all transmissions containing a Packet Error Code (PEC). //! //! The PEC is calculated over the whole transmission including address and read/write bit. //! The polynomial used is `x^8 + x^2 + x + 1`, which corresponds to [CRC-8-ATM HEC][crc8] //! initialized to zero. //! //! [crc8]: https://en.wikipedia.org/wiki/CRC-8 //! [smbus]: https://en.wikipedia.org/wiki/System_Management_Bus //! [smbus-pec]: https://en.wikipedia.org/wiki/System_Management_Bus#Packet_Error_Checking //! //! # How this crate compares to others //! //! There is a number of crates implementing CRC algorithms but their intention is to //! be configurable, generic, use acceleration via SIMD instructions, etc. //! //! This crate provides a portable and non-configurable implementation of exactly one //! algorithm: The one used for SMBus PEC (optionally using a pre-calculated lookup table). //! //! This should allow the compiler to make good optimizations and allows for use of the //! algorithm in any target architecture with minimal code bloat. //! //! This makes this crate specially well suited for use in `no_std` environments. //! //! # Pre-calculated lookup table //! //! A faster version of the algorithm is provided through the use of a pre-calculated //! lookup table. This can be enabled through the `lookup-table` feature. //! //! With this feature enabled a table of 256 pre-calculated `u8` values will be included //! which avoids bit-by-bit calculation at the cost of the space needed to store it. //! //! # Usage //! //! ## Send command with a value to an address using function //! //! A typical use case for this would be writing the value to a register //! //! ```rust //! # struct Smbus; //! # impl Smbus { //! # fn write(&mut self, address: u8, data: &[u8]) {} //! # } //! # //! # let mut smbus = Smbus {}; //! # //! use smbus_pec::pec; //! const ADDR: u8 = 0x5A; //! let command = 0x06; //! let value = 0xAB; //! //! let checksum = pec(&[ADDR << 1, command, value]); //! smbus.write(ADDR, &[command, value, checksum]); //! ``` //! //! ## Perform request-response using function //! //! A typical use case for this would be reading the value of a register. //! To do this, a write with the register address is sent, followed by a read. //! //! ```rust //! # struct Smbus; //! # impl Smbus { //! # fn write_read(&mut self, address: u8, data: &[u8], buffer: &mut [u8]) {} //! # } //! # //! # let mut smbus = Smbus {}; //! # //! use smbus_pec::pec; //! const ADDR: u8 = 0x5A; //! let register = 0x06; //! let mut data = [0; 2]; //! //! smbus.write_read(ADDR, &[register], &mut data); //! let checksum = pec(&[ADDR << 1, register, (ADDR << 1) | 1, data[0]]); //! if checksum != data[1] { //! println!("Packet Error Code mismatch."); //! } //! let value = data[0]; //! ``` //! //! ## Send command with a value to an address using hasher //! //! A typical use case for this would be writing the value to a register //! //! ```rust //! # struct Smbus; //! # impl Smbus { //! # fn write(&mut self, address: u8, data: &[u8]) {} //! # } //! # //! # let mut smbus = Smbus {}; //! # //! use core::hash::Hasher; //! use smbus_pec::Pec; //! const ADDR: u8 = 0x5A; //! let command = 0x06; //! let value = 0xAB; //! //! let mut hasher = Pec::new(); //! hasher.write(&[ADDR << 1, command, value]); //! let checksum = hasher.finish() as u8; //! smbus.write(ADDR, &[command, value, checksum]); //! ``` //! //! ## Perform request-response using hasher //! //! A typical use case for this would be reading the value of a register. //! To do this, a write with the register address is sent, followed by a read. //! //! ```rust //! # struct Smbus; //! # impl Smbus { //! # fn write_read(&mut self, address: u8, data: &[u8], buffer: &mut [u8]) {} //! # } //! # //! # let mut smbus = Smbus {}; //! # //! use core::hash::Hasher; //! use smbus_pec::Pec; //! const ADDR: u8 = 0x5A; //! let register = 0x06; //! let mut data = [0; 2]; //! //! smbus.write_read(ADDR, &[register], &mut data); //! let mut hasher = Pec::new(); //! hasher.write(&[ADDR << 1, register, (ADDR << 1) | 1, data[0]]); //! let checksum = hasher.finish(); //! if checksum != data[1] as u64 { //! println!("Packet Error Code mismatch."); //! } //! let value = data[0]; //! ``` //! #![doc(html_root_url = "https://docs.rs/smbus-pec/1.0.0")] #![deny(unsafe_code, missing_docs)] #![no_std] #[cfg(not(feature = "lookup-table"))] mod default_impl { use embedded_crc_macros::{crc8, crc8_hasher}; crc8!( fn pec, 7, 0, "Calculate SMBus Packet Error Code over transmitted data.\ \n\nThe input data array must contain the complete message including address and read/write bit." ); crc8_hasher!( struct Pec, 7, 0, "Calculate SMBus Packet Error Code over transmitted data. `core::hash::Hasher` implementation.\ \n\nThe input data array must contain the complete message including address and read/write bit.\ \n\nNote that the hasher holds an internal state so that it is possible to call `write()` \ several times. A new instance must be created for each independent calculation." ); } #[cfg(not(feature = "lookup-table"))] pub use crate::default_impl::{pec, Pec}; #[cfg(feature = "lookup-table")] mod lookup_table_impl { use crate::LOOKUP_TABLE; use embedded_crc_macros::{crc8_hasher_lookup_table, crc8_lookup_table}; crc8_lookup_table!( fn pec, 0, LOOKUP_TABLE, "Calculate SMBus Packet Error Code over transmitted data.\ \n\nThe input data array must contain the complete message including address and read/write bit. \n\nThis implementation uses a lookup table and is much faster at the cost of some space." ); crc8_hasher_lookup_table!( struct Pec, 0, LOOKUP_TABLE, "Calculate SMBus Packet Error Code over transmitted data. `core::hash::Hasher` implementation.\ \n\nThe input data array must contain the complete message including address and read/write bit.\ \n\nNote that the hasher holds an internal state so that it is possible to call `write()` \ several times. A new instance must be created for each independent calculation." ); } #[cfg(feature = "lookup-table")] pub use crate::lookup_table_impl::{pec, Pec}; #[cfg(feature = "lookup-table")] include!(concat!(env!("OUT_DIR"), "/lookup_table.rs"));