[−][src]Crate bounded_registers
Bounded Registers
A high-assurance memory-mapped register code generation and interaction library.
Install
$ git clone git@github.com:auxoncorp/registers.git
$ cd registers && cargo install
Use
There are two core pieces to bounded-registers
:
I. The macro
register! { Status, u8, RW, Fields [ On WIDTH(U1) OFFSET(U0), Dead WIDTH(U1) OFFSET(U1), Color WIDTH(U3) OFFSET(U2) [ Red = U1, Blue = U2, Green = U3, Yellow = U4 ] ] }
The register!
macro generates the code necessary for ergonomic
register access and manipulation. The expected input for the macro is
as follows:
- The register name.
- Its numeric type.
- Its mode, either
RO
(read only),RW
(read write), orWO
(write only). - The register's fields, beginning with
Fields [
, and then a closing]
at the end.
A field constists of its name, its width, and its offset within the
register. Optionally, one may also state enum-like key/value pairs for
the values of the field, nested within the field declaration with
[]
's
The code which this macro generates is a tree of nested modules where
the root is a module called $register_name
. Within $register_name
,
there will be the register itself, as $register_name::Register
, as
well as a child module for each field.
Within each field module, one can find the field itself, as
$register_name::$field_name::Field
, as well as a few helpful aliases
and constants.
$register_name::$field_name::Read
: In order to read a field, an instance of that field must be given to have access to its mask and offset.Read
can be used as an argument toget_field
so one does not have to construct an arbitrary one when doing a read.$register_name::$field_name::Clear
: A field whose value is zero. Passing it tomodify
will clear that field in the register.$register_name::$field_name::Set
: A field whose value is$field_max
. Passing it tomodify
will set that field to its max value in the register. This is useful particularly in the case of single-bit wide fields.$register_name::$field_name::$enum_kvs
: constants mapping the enum like field names to values.
II. Interacting with registers
Through a constructor
fn main() { let mut reg = Status::Register::new(0); reg.modify(Status::Dead::Set); assert_eq!(reg.read(), 2); }
In this example, we initialize a register with the value 0
and then
set the Dead
bit—the second field—which should produce the value 2
when interpreting this word-sized register as a u32
.
Through a register block
Here we take a known address, one we may find in a developer's manual, and interpret that address as a register block. We can then dereference that pointer and use the register API to access the registers in the block.
You can then implement Deref
and DerefMut
for a type which holds
onto the address of such a register block. This fills in the gaps for
method lookup (during typechecking) so that you can ergonomically use
this type to interact with the register block:
#[macro_use] extern crate bounded_registers; #[macro_use] extern crate typenum; use core::ops::{Deref, DerefMut}; register! { UartRX, u32, RO, Fields [ Data WIDTH(U8) OFFSET(U0), ParityError WIDTH(U1) OFFSET(U10), Brk WIDTH(U1) OFFSET(U11), FrameError WIDTH(U1) OFFSET(U12), Overrrun WIDTH(U1) OFFSET(U13), Error WIDTH(U1) OFFSET(U14), ChrRdy WIDTH(U1) OFFSET(U15) ] } register! { UartTX, u32, WO, Fields [ Data WIDTH(U8) OFFSET(U0) ] } register! { UartControl1, u32, RW, Fields [ Enable WIDTH(U1) OFFSET(U0), Doze WIDTH(U1) OFFSET(U1), AgingDMATimerEnable WIDTH(U1) OFFSET(U2), TxRdyDMAENable WIDTH(U1) OFFSET(U3), SendBreak WIDTH(U1) OFFSET(U4), RTSDeltaInterrupt WIDTH(U1) OFFSET(U5), TxEmptyInterrupt WIDTH(U1) OFFSET(U6), Infrared WIDTH(U1) OFFSET(U7), RecvReadyDMA WIDTH(U1) OFFSET(U8), RecvReadyInterrupt WIDTH(U1) OFFSET(U9), IdleCondition WIDTH(U2) OFFSET(U10), IdleInterrupt WIDTH(U1) OFFSET(U12), TxReadyInterrupt WIDTH(U1) OFFSET(U13), AutoBaud WIDTH(U1) OFFSET(U14), AutoBaudInterrupt WIDTH(U1) OFFSET(U15) ] } #[repr(C)] pub struct UartBlock { rx: UartRX::Register, _padding1: [u32; 15], tx: UartTX::Register, _padding2: [u32; 15], control1: UartControl1::Register, } pub struct Regs { addr: usize, } impl Deref for Regs { type Target = UartBlock; fn deref(&self) -> &UartBlock { unsafe { &*(self.addr as *const UartBlock) } } } impl DerefMut for Regs { fn deref_mut(&mut self) -> &mut UartBlock { unsafe { &mut *(self.addr as *mut UartBlock) } } } fn main() { let mut x = [0_u32; 33]; let mut regs = Regs { // Some shenanigans to get at `x` as though it were a // pointer. Normally you'd be given some address like // `0xDEADBEEF` over which you'd instantiate a `Regs`. addr: &mut x as *mut [u32; 33] as usize, }; assert_eq!(regs.rx.read(), 0); regs.control1 .modify(UartControl1::Enable::Set + UartControl1::RecvReadyInterrupt::Set); // The first bit and the 10th bit should be set. assert_eq!(regs.control1.read(), 0b_10_0000_0001); }
The Register API
The register API code is generated with docs, but you'll have to build
the rustdoc documentation for your library that uses
bounded-registers
to be able to see it. For convenience, I've
extrapolated it here:
/// `new` constructs a read-write register around the /// given pointer. fn new(init: Width) -> Self; /// `get_field` takes a field and sets the value of that /// field to its value in the register. fn get_field<M: Unsigned, O: Unsigned, U: Unsigned>( &self, f: Field<Width, M, O, U, Register>, ) -> Option<Field<Width, M, O, U, Register>> where U: IsGreater<U0, Output = True> + ReifyTo<Width>, M: ReifyTo<Width>, O: ReifyTo<Width>, U0: ReifyTo<Width>; /// `read` returns the current state of the register as a `Width`. fn read(&self) -> Width; /// `extract` pulls the state of a register out into a wrapped /// read-only register. fn extract(&self) -> ReadOnlyCopy<Width, Register>; /// `is_set` takes a field and returns true if that field's value /// is equal to its upper bound or not. This is of particular use /// in single-bit fields. fn is_set<M: Unsigned, O: Unsigned, U: Unsigned>( &self, f: Field<Width, M, O, U, Register>, ) -> bool where U: IsGreater<U0, Output = True>, U: ReifyTo<Width>, M: ReifyTo<Width>, O: ReifyTo<Width>; // `Positioned` is a special trait that all fields implement, as // well as a type used as an accumulator when reading from or // writing to multiple fields. To use these functions with // multiple fields, join them together with `+`. An `Add` // implementation for fields has been provided for this purpose. /// `matches_any` returns whether or not any of the given fields /// match those fields values inside the register. fn matches_any<V: Positioned<Width = Width>>(&self, val: V) -> bool; /// `matches_all` returns whether or not all of the given fields /// match those fields values inside the register. fn matches_all<V: Positioned<Width = Width>>(&self, val: V) -> bool; /// `modify` takes one or more fields, joined by `+`, and /// sets those fields in the register, leaving the others /// as they were. fn modify<V: Positioned<Width = Width>>(&mut self, val: V); /// `write` sets the value of the whole register to the /// given `Width` value. fn write(&mut self, val: Width);
Theory
bounded-registers
employs values—specifically numbers—at the
type-level in order to get compile time assertions on interactions
with a register. Each field's width is used to determine a maximum
value, and then reading from and writing to those fields is either
checked at compile time, through the checked
function, or is
expected to carry a proof, which uses the aforementioned bound
to construct a value at runtime which is known to not contravene
it.
Modules
bounds | |
macros |
Macros
register | The |
Structs
Field | A field in a register parameterized by its mask, offset, and upper
bound. To construct a field, its |
FieldDisj |
|
ReadOnlyCopy |
Traits
Pointer | |
Positioned |
|