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218 lines
6.4 KiB
Rust
218 lines
6.4 KiB
Rust
//! Implement the Field structure.
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use core::ptr::{read_volatile, write_volatile};
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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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///
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/// TODO: Mark write method as unsafe?
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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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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 {
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address,
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offset,
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size,
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mask,
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}
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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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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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/// Set the value of the field in the provided u32.
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#[inline]
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pub fn read_and_write_to_u32(&self, val: u32, register: u32) -> u32 {
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assert_eq!(
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val & !(self.mask >> self.offset),
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0,
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"Value greater than the field"
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);
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register & !self.mask | (val << self.offset)
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}
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/// Get the value of the field from the provided u32.
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#[inline]
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pub fn read_from_u32(&self, register: u32) -> u32 {
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(register & self.mask) >> self.offset
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}
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/// Write the value in memory.
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pub fn read_and_write(&self, val: u32) {
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let register = unsafe { read_volatile(self.address as *mut u32) };
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let register = self.read_and_write_to_u32(val, register);
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unsafe { write_volatile(self.address as *mut u32, register) };
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}
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/// Write the value in memory but override every other value of the
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/// u32 (replace them by 0s).
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pub fn write_without_read(&self, val: u32) {
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let register = self.read_and_write_to_u32(val, 0);
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unsafe { write_volatile(self.address as *mut u32, register) };
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}
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/// Read the value from memory.
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pub fn read(&self) -> u32 {
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let register = unsafe { read_volatile(self.address as *mut u32) };
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self.read_from_u32(register)
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}
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}
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn test_get_address() {
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// Test when the address is alligned
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assert_eq!(Field::new(0x1234_5678, 0, 1).get_address(), 0x1234_5678,);
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}
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#[test]
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fn test_get_offset() {
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assert_eq!(Field::new(0x1234_5678, 18, 1).get_offset(), 18,);
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}
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#[test]
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fn test_get_size() {
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assert_eq!(Field::new(0x1234_5678, 18, 1).get_size(), 1,);
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}
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#[test]
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fn test_alignment_enforcement() {
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let field = Field::new(0x1111_1110, 0, 1);
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assert_eq!(field.get_address(), 0x1111_1110);
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assert_eq!(field.get_offset(), 0);
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let field = Field::new(0x1111_1111, 0, 1);
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assert_eq!(field.get_address(), 0x1111_1110);
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assert_eq!(field.get_offset(), 8);
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let field = Field::new(0x1111_1112, 0, 1);
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assert_eq!(field.get_address(), 0x1111_1110);
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assert_eq!(field.get_offset(), 16);
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let field = Field::new(0x1111_1113, 0, 1);
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assert_eq!(field.get_address(), 0x1111_1110);
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assert_eq!(field.get_offset(), 24);
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}
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#[test]
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fn test_closeness_enforcement() {
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let field = Field::new(0x1111_1110, 32, 1);
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assert_eq!(field.get_address(), 0x1111_1114);
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assert_eq!(field.get_offset(), 0);
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let field = Field::new(0x1111_1111, 32, 1);
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assert_eq!(field.get_address(), 0x1111_1114);
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assert_eq!(field.get_offset(), 8);
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let field = Field::new(0x1111_1112, 32 + 16, 1);
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assert_eq!(field.get_address(), 0x1111_1118);
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assert_eq!(field.get_offset(), 0);
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}
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#[test]
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#[should_panic]
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fn test_prevent_overlaps() {
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let _ = Field::new(0, 24, 16);
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}
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#[test]
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fn test_get_mask() {
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assert_eq!(Field::new(0, 0, 1).get_mask(), 0b0000_0001,);
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assert_eq!(Field::new(0, 0, 3).get_mask(), 0b0000_0111,);
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assert_eq!(Field::new(0, 4, 1).get_mask(), 0b0001_0000,);
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assert_eq!(Field::new(0, 4, 3).get_mask(), 0b0111_0000,);
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}
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#[test]
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fn test_read_and_write_to_u32() {
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let field = Field::new(0, 3, 4);
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let val = 0b0101_0101;
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assert_eq!(field.read_and_write_to_u32(0b0101, val), 0b0010_1101,);
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}
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#[test]
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#[should_panic]
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fn test_read_and_write_to_u32_too_big() {
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let field = Field::new(0, 0, 3);
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let _ = field.read_and_write_to_u32(0b1111, 0);
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}
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#[test]
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fn test_read_from_u32() {
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let field = Field::new(0, 3, 4);
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let val = 0b1100_1111;
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assert_eq!(field.read_from_u32(val), 0b1001,);
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}
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}
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