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riscv: define mvendorid CSR with macro helpers #255

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riscv: define mvendorid CSR with macro helpers #255

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1 change: 1 addition & 0 deletions riscv/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
- Use CSR helper macros to define `mstatus` register
- Use CSR helper macros to define `mstatush` register
- Use CSR helper macros to define `mtvec` register
- Use CSR helper macros to define `mtvendorid` register

## [v0.12.1] - 2024-10-20

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48 changes: 22 additions & 26 deletions riscv/src/register/mvendorid.rs
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@@ -1,34 +1,30 @@
//! mvendorid register

use core::num::NonZeroUsize;

/// mvendorid register
#[derive(Clone, Copy, Debug)]
pub struct Mvendorid {
bits: NonZeroUsize,
read_only_csr! {
/// `mvendorid` register
Mvendorid: 0xF11,
mask: 0xffff_ffff,
sentinel: 0,
}

impl Mvendorid {
/// Returns the contents of the register as raw bits
#[inline]
pub fn bits(&self) -> usize {
self.bits.get()
}

/// Returns the JEDEC manufacturer ID
#[inline]
pub fn jedec_manufacturer(&self) -> usize {
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Should we add the jedec_manufacturer field?

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Good question, I missed that function when converting to the CSR macro.

After reading the ISA again, it looks like the jedec_manufacturer implementation was incorrect.

mvendorid encodes the number of one-byte continuation codes in the Bank field, and
encodes the final byte in the Offset field, discarding the parity bit. For example, the JEDEC
manufacturer ID 0x7f 0x7f 0x7f 0x7f 0x7f 0x7f 0x7f 0x7f 0x7f 0x7f 0x7f 0x7f 0x8a (twelve
continuation codes followed by 0x8a) would be encoded in the mvendorid CSR as 0x60a.

So, we would probably want to add bank and offset fields, along with a correct jedec_manufacturer function that decodes the ID:

pub const fn jedec_manufacturer(&self) -> (usize, usize) {
    (self.bank(), 0x80 | self.offset())
}

self.bits() >> 7
}
read_only_csr_field! {
Mvendorid,
/// Represents the number of continuation bytes (`0x7f`) in the JEDEC manufacturer ID.
bank: [7:31],
}

read_csr!(0xF11);
read_only_csr_field! {
Mvendorid,
/// Represents the final offset field in the JEDEC manufacturer ID.
offset: [0:6],
}

/// Reads the CSR
#[inline]
pub fn read() -> Option<Mvendorid> {
let r = unsafe { _read() };
// When mvendorid is hardwired to zero it means that the mvendorid
// csr isn't implemented.
NonZeroUsize::new(r).map(|bits| Mvendorid { bits })
impl Mvendorid {
/// Gets the JEDEC manufacturer ID decoded into parts:
///
/// - `bank`: the number of continuation bytes (`0x7f`)
/// - `offset`: specific offset in the JEDEC bank number
pub fn jedec_manufacturer(&self) -> (usize, usize) {
(self.bank(), (0x80 | self.offset()))
}
}
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