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✨ Implement read-only and write-only fields
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This is useful when implement drivers for memory mapped I/O. Some of the
device registers should only be read/written, but not the opposite.

Fixes #27
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@paul1999 @wrenger
paul1999 authored and wrenger committed Dec 10, 2023
1 parent 85df1f6 commit 6a4adab
Showing 1 changed file with 121 additions and 40 deletions.
161 changes: 121 additions & 40 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -410,6 +410,7 @@ struct Member {
bits: usize,
base_ty: syn::Type,
default: TokenStream,
access: AccessMode,
inner: Option<MemberInner>,
}

Expand Down Expand Up @@ -449,6 +450,7 @@ impl Member {
mut default,
into,
from,
access,
} = parse_field(&base_ty, &attrs, &ty, ignore)?;

if bits > 0 && !ignore {
Expand Down Expand Up @@ -485,6 +487,7 @@ impl Member {
bits,
base_ty,
default,
access,
inner: Some(MemberInner {
ident,
ty,
Expand All @@ -504,31 +507,39 @@ impl Member {
bits,
base_ty,
default,
access,
inner: None,
})
}
}

fn debug(&self) -> TokenStream {
if let Some(inner) = &self.inner {
let ident_str = inner.ident.to_string();
let ident = &inner.ident;
quote!(.field(#ident_str, &self.#ident()))
} else {
quote!()
match (&self.inner, self.access) {
(Some(inner), AccessMode::ReadWrite | AccessMode::ReadOnly) => {
let ident_str = inner.ident.to_string();
let ident = &inner.ident;
quote!(.field(#ident_str, &self.#ident()))
},
_ => {
quote!()
}
}
}

fn default(&self) -> TokenStream {
let default = &self.default;
if let Some(inner) = &self.inner {
let ident = &inner.ident;
let with_ident = format_ident!("with_{ident}");
quote!(this = this.#with_ident(#default);)
} else {
let offset = self.offset;
let base_ty = &self.base_ty;
quote!(this.0 |= (#default as #base_ty) << #offset;)

match (&self.inner, self.access) {
(Some(inner), AccessMode::ReadWrite | AccessMode::WriteOnly) => {
let ident = &inner.ident;
let with_ident = format_ident!("with_{ident}");
quote!(this = this.#with_ident(#default);)
}
_ => {
let offset = self.offset;
let base_ty = &self.base_ty;
quote!(this.0 |= (#default as #base_ty) << #offset;)
}
}
}
}
Expand All @@ -540,6 +551,7 @@ impl ToTokens for Member {
bits,
base_ty,
default: _,
access,
inner:
Some(MemberInner {
ident,
Expand Down Expand Up @@ -572,36 +584,46 @@ impl ToTokens for Member {
let mask = u128::MAX >> (u128::BITS - *bits as u32);
let mask = syn::LitInt::new(&format!("0x{mask:x}"), Span::mixed_site());

let code = quote! {
let mut code = quote! {
const #bits_ident: usize = #bits;
const #offset_ident: usize = #offset;
};

#doc
#[doc = #location]
#[cfg_attr(debug_assertions, track_caller)]
#vis const fn #with_ident(self, value: #ty) -> Self {
let value: #base_ty = {
let this = value;
#into
};
#[allow(unused_comparisons)]
debug_assert!(value <= #mask, "value out of bounds");
Self(self.0 & !(#mask << #offset) | (value & #mask) << #offset)
}
#doc
#[doc = #location]
#vis const fn #ident(&self) -> #ty {
let this = (self.0 >> #offset) & #mask;
#from
}
#doc
#[doc = #location]
#[cfg_attr(debug_assertions, track_caller)]
#vis fn #set_ident(&mut self, value: #ty) {
*self = self.#with_ident(value);
}
if matches!(access, AccessMode::ReadWrite | AccessMode::ReadOnly) {
code.extend(quote! {
#doc
#[doc = #location]
#vis const fn #ident(&self) -> #ty {
let this = (self.0 >> #offset) & #mask;
#from
}
});
}

if matches!(access, AccessMode::ReadWrite | AccessMode::WriteOnly) {
code.extend(quote! {
#doc
#[doc = #location]
#[cfg_attr(debug_assertions, track_caller)]
#vis const fn #with_ident(self, value: #ty) -> Self {
let value: #base_ty = {
let this = value;
#into
};
#[allow(unused_comparisons)]
debug_assert!(value <= #mask, "value out of bounds");
Self(self.0 & !(#mask << #offset) | (value & #mask) << #offset)
}

#doc
#[doc = #location]
#[cfg_attr(debug_assertions, track_caller)]
#vis fn #set_ident(&mut self, value: #ty) {
*self = self.#with_ident(value);
}
});
}

};
tokens.extend(code);
}
}
Expand All @@ -627,6 +649,8 @@ struct Field {
default: TokenStream,
into: TokenStream,
from: TokenStream,

access: AccessMode,
}

/// Parses the `bits` attribute that allows specifying a custom number of bits.
Expand All @@ -641,6 +665,12 @@ fn parse_field(
e
}

let default_access = if ignore {
AccessMode::None
} else {
AccessMode::ReadWrite
};

// Defaults for the different types
let (class, ty_bits) = type_bits(ty);
let mut ret = match class {
Expand All @@ -650,27 +680,31 @@ fn parse_field(
default: quote!(false),
into: quote!(this as _),
from: quote!(this != 0),
access: default_access,
},
TypeClass::SInt => Field {
bits: ty_bits,
ty: ty.clone(),
default: quote!(0),
into: quote!(),
from: quote!(),
access: default_access,
},
TypeClass::UInt => Field {
bits: ty_bits,
ty: ty.clone(),
default: quote!(0),
into: quote!(this as _),
from: quote!(this as _),
access: default_access,
},
TypeClass::Other => Field {
bits: ty_bits,
ty: ty.clone(),
default: quote!(),
into: quote!(#ty::into_bits(this)),
from: quote!(#ty::from_bits(this)),
access: default_access,
},
};

Expand All @@ -691,6 +725,7 @@ fn parse_field(
default,
into,
from,
access,
} = syn::parse2(tokens.clone()).map_err(|e| malformed(e, attr))?;

// bit size
Expand All @@ -711,6 +746,14 @@ fn parse_field(
));
}

// Ensure padding fields remain inaccesible
if ignore && access.is_some_and(|mode| mode != AccessMode::None) {
return Err(syn::Error::new(
default.span(),
"'access' may only be 'None' (or unset) for padding",
));
}

// conversion
if let Some(into) = into {
ret.into = quote!(#into(this));
Expand All @@ -726,6 +769,11 @@ fn parse_field(
if let Some(default) = default {
ret.default = default.into_token_stream();
}

// access mode
if let Some(access) = access {
ret.access = access;
}
}
}

Expand Down Expand Up @@ -769,6 +817,7 @@ struct BitsAttr {
default: Option<syn::Expr>,
into: Option<syn::Path>,
from: Option<syn::Path>,
access: Option<AccessMode>,
}

impl Parse for BitsAttr {
Expand All @@ -778,6 +827,7 @@ impl Parse for BitsAttr {
default: None,
into: None,
from: None,
access: None,
};
if let Ok(bits) = syn::LitInt::parse(input) {
attr.bits = Some(bits.base10_parse()?);
Expand All @@ -798,6 +848,8 @@ impl Parse for BitsAttr {
attr.into = Some(input.parse()?);
} else if ident == "from" {
attr.from = Some(input.parse()?);
} else if ident == "access" {
attr.access = Some(input.parse()?);
}

if input.is_empty() {
Expand All @@ -811,6 +863,35 @@ impl Parse for BitsAttr {
}
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum AccessMode {
ReadWrite,
ReadOnly,
WriteOnly,
None,
}

impl Parse for AccessMode {
fn parse(input: ParseStream) -> syn::Result<Self> {
let mode = input.parse::<Ident>()?;

if mode == "RW" {
Ok(AccessMode::ReadWrite)
} else if mode == "RO" {
Ok(AccessMode::ReadOnly)
} else if mode == "WO" {
Ok(AccessMode::WriteOnly)
} else if mode == "None" {
Ok(AccessMode::None)
} else {
Err(syn::Error::new(
mode.span(),
"Invalid access mode, only RW/RO/WO/None are allowed",
))
}
}
}

#[derive(Clone, Copy, PartialEq)]
enum Order {
Lsb,
Expand Down

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