svd2rust 0.2.1

Generate Rust register maps (`struct`s) from SVD files

Generate Rust register maps (structs) from SVD files

Changelog

Installation

$ cargo install svd2rust

Usage

  • Get the start/base address of each peripheral's register block.
$ svd2rust -i STM32F30x.svd
const GPIOA: usize = 0x48000000;
const GPIOB: usize = 0x48000400;
const GPIOC: usize = 0x48000800;
const GPIOD: usize = 0x48000c00;
const GPIOE: usize = 0x48001000;
const GPIOF: usize = 0x48001400;
const TSC: usize = 0x40024000;
const CRC: usize = 0x40023000;
const Flash: usize = 0x40022000;
const RCC: usize = 0x40021000;
  • Generate a register map for a single peripheral.
$ svd2rust -i STM32F30x.svd rcc | head
/// Reset and clock control
#[repr(C)]
pub struct Rcc {
    /// 0x00 - Clock control register
    pub cr: Cr,
    /// 0x04 - Clock configuration register (RCC_CFGR)
    pub cfgr: Cfgr,
    /// 0x08 - Clock interrupt register (RCC_CIR)
    pub cir: Cir,
    /// 0x0c - APB2 peripheral reset register (RCC_APB2RSTR)

API

The svd2rust generates the following API for each peripheral:

Register block

A register block "definition" as a struct. Example below:

/// Inter-integrated circuit
#[repr(C)]
pub struct I2c1 {
    /// 0x00 - Control register 1
    pub cr1: Cr1,
    /// 0x04 - Control register 2
    pub cr2: Cr2,
    /// 0x08 - Own address register 1
    pub oar1: Oar1,
    /// 0x0c - Own address register 2
    pub oar2: Oar2,
    /// 0x10 - Timing register
    pub timingr: Timingr,
    /// 0x14 - Status register 1
    pub timeoutr: Timeoutr,
    /// 0x18 - Interrupt and Status register
    pub isr: Isr,
    /// 0x1c - Interrupt clear register
    pub icr: Icr,
    /// 0x20 - PEC register
    pub pecr: Pecr,
    /// 0x24 - Receive data register
    pub rxdr: Rxdr,
    /// 0x28 - Transmit data register
    pub txdr: Txdr,
}

The user has to "instantiate" this definition for each peripheral the microcontroller has. They have two choices:

  • static variables. Example below:
extern "C" {
    // I2C1 can be accessed in read-write mode
    pub static mut I2C1: I2c;
    // whereas I2C2 can only be accessed in "read-only" mode
    pub static I2C1: I2c;
}

here the addresses of these register blocks must be provided by a linker script:

/* layout.ld */
I2C1 = 0x40005400;
I2C2 = 0x40005800;

This has the side effect that the I2C1 and I2C2 symbols get "taken" so no other C/Rust symbol (static, function, etc.) can have the same name.

  • "constructor" functions. Example below:
// Base addresses of the register blocks. These are private.
const I2C1: usize = 0x40005400;
const I2C2: usize = 0x40005800;

// NOTE(unsafe) hands out aliased `&mut-` references
pub unsafe fn i2c1() -> &'static mut I2C {
    unsafe { &mut *(I2C1 as *mut I2c) }
}

pub fn i2c2() -> &'static I2C {
    unsafe { &*(I2C2 as *const I2c) }
}

read / modify / write

Each register in the register block, e.g. the cr1 field in the I2c struct, exposes a combination of the read, modify and write methods. Which methods exposes each register depends on whether the register is read-only, read-write or write-only:

  • read-only registers only expose the read method.
  • write-only registers only expose the write method.
  • read-write registers expose all the methods: read, modify and write.

This is signature of each of these methods:

(using the CR2 register as an example)

impl Cr2 {
    pub fn modify<F>(&mut self, f: F)
        where for<'w> F: FnOnce(&Cr2R, &'w mut Cr2W) -> &'w mut Cr2W
    {
        ..
    }

    pub fn read(&self) -> Cr2R { .. }

    pub fn write<F>(&mut self, f: F)
        where F: FnOnce(&mut Cr2W) -> &mut Cr2W,
    {
        ..
    }
}

The read method "reads" the register using a single, volatile LDR instruction and returns a proxy Cr2R struct that allows access to only the readable bits (i.e. not to the reserved or write-only bits) of the CR2 register:

impl Cr2R {
    /// Bit 0 - Slave address bit 0 (master mode)
    pub fn sadd0(&self) -> bool { .. }

    /// Bits 1:7 - Slave address bit 7:1 (master mode)
    pub fn sadd1(&self) -> u8 { .. }

    (..)
}

Usage looks like this:

// is the SADD0 bit of the CR2 register set?
if i2c1.c2r.read().sadd0() {
    // something
} else {
    // something else
}

The write method writes some value to the register using a single, volatile STR instruction. This method involves a Cr2W struct that only allows constructing valid states of the CR2 register.

The only constructor that Cr2W provides is reset_value which returns the value of the CR2 register after a reset. The rest of Cr2W methods are "builder-like" and can be used to set or reset the writable bits of the CR2 register.

impl Cr2W {
    /// Reset value
    pub fn reset_value() -> Self {
        Cr2W { bits: 0 }
    }

    /// Bits 1:7 - Slave address bit 7:1 (master mode)
    pub fn sadd1(&mut self, value: u8) -> &mut Self { .. }

    /// Bit 0 - Slave address bit 0 (master mode)
    pub fn sadd0(&mut self, value: bool) -> &mut Self { .. }
}

The write method takes a closure with signature &mut Cr2W -> &mut Cr2W. If the "identity closure", |w| w, is passed then write method will set the CR2 register to its reset value. Otherwise, the closure specifies how that reset value will be modified before it's written to CR2.

Usage looks like this:

// Write to CR2, its reset value (`0x0000_0000`) but with its SADD0 and
// SADD1 fields set to `true` and `0b0011110` respectively
i2c1.cr2.write(|w| w.sadd0(true).sadd1(0b0011110));

Finally, the modify method performs a single read-modify-write operation that involves reading (LDR) the register, modifying the fetched value and then writing (STR) the modified value to the register. This method accepts a closure that specifies how the CR2 register will be modified (the w argument) and also provides access to the state of the register before it's modified (the r argument).

Usage looks like this:

// Set the START bit to 1 while KEEPING the state of the other bits intact
i2c1.cr2.modify(|_, w| w.start(true));

// TOGGLE the STOP bit
i2c1.cr2.modify(|r, w| w.stop(!r.stop()));