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84 lines
2.5 KiB
Rust
84 lines
2.5 KiB
Rust
//! Implement the Field structure.
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/// Structure representing the location of a register.
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/// This structure does not provide any kind of safety, it
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/// is only descriptif.
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///
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/// Fields represent a continuous set of bits in an alligned
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/// `u32`. This means that the address is a multiple of 4,
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/// the offset is < 32, and offset + size <= 32.
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///
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/// The constructor of the is class ensure that the field is
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/// always inside the `u32` at `address`, and that `address`
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/// is alligned.
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pub struct Field {
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/// The address of the discribed field.
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address: usize,
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/// The offset of the first bit of the field relative to the
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/// address.
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offset: usize,
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/// The size of the field in bit.
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size: usize,
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/// The mask for the field in the `u32` at `address`.
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mask: u32
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}
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// TODO: test
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impl Field {
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/// Constructor for a Field.
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/// The field is defined by the `size` bits at `offset` bits after
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/// `address`. (**`address` is in bytes, not bits**)
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pub const fn new(address: usize, offset: usize, size: usize) -> Self {
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// align the address
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let offset = offset + 8 * (address % 4);
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let address = address - (address % 4);
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// make sure the field is in the u32 at address
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let address = address + 4 * (offset / 32);
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let offset = offset % 32;
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// make sure the field does not overlap with the next u32
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if offset + size > 32 {
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panic!("A field can not overlap two aligned `u32`");
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}
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let mask = Self::compute_mask(offset, size);
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Self { address, offset, size, mask }
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}
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/// Compute mask for the field.
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const fn compute_mask(offset: usize, size: usize) -> u32 {
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let mut mask = 0u32;
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// Const functions don't allow for loops.
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let mut i = 0;
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while i < size {
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mask <<= 1;
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mask |= 1;
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i += 1;
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}
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mask <<= offset;
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mask
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}
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/// Return the address of the `u32` containing the field.
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pub const fn get_address(&self) -> usize {
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self.address
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}
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/// Return the offset of the field in relation to the address, in bits.
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#[allow(dead_code)]
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pub const fn get_offset(&self) -> usize {
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self.offset
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}
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/// Return the size of the field in bit.
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#[allow(dead_code)]
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pub const fn get_size(&self) -> usize {
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self.size
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}
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/// Return the mask of the field in the `u32` at `address`.
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pub const fn get_mask(&self) -> u32 {
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self.mask
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}
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}
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