use ConstDefault instead of Default

ci/script.sh

@@ -43,6 +43,7 @@ main() {
     echo 'cortex-m = "0.7.7"'    >> $td/Cargo.toml
     echo 'cortex-m-rt = "0.7.3"' >> $td/Cargo.toml
     echo 'vcell = "0.1.3"'       >> $td/Cargo.toml
+    echo 'const-default = "1.0"' >> $td/Cargo.toml
     if [[ "$options" == *"--atomics"* ]]; then
         echo 'portable-atomic = { version = "1.4", default-features = false }' >> $td/Cargo.toml
     fi

ci/svd2rust-regress/src/svd_test.rs

@@ -11,7 +11,11 @@ use std::{
     path::Path,
 };
 
-const CRATES_ALL: &[&str] = &["critical-section = \"1.0\"", "vcell = \"0.1.2\""];
+const CRATES_ALL: &[&str] = &[
+    "critical-section = \"1.0\"",
+    "vcell = \"0.1.2\"",
+    "const-default = \"1.0\"",
+];
 const CRATES_MSP430: &[&str] = &["msp430 = \"0.4.0\"", "msp430-rt = \"0.4.0\""];
 const CRATES_ATOMICS: &[&str] =
     &["portable-atomic = { version = \"0.3.16\", default-features = false }"];

src/generate/generic.rs

@@ -1,9 +1,10 @@
 use core::marker;
+use const_default::ConstDefault;
 
 /// Raw register type (`u8`, `u16`, `u32`, ...)
 pub trait RawReg:
     Copy
-    + Default
+    + ConstDefault
     + From<bool>
     + core::ops::BitOr<Output = Self>
     + core::ops::BitAnd<Output = Self>
@@ -74,10 +75,10 @@ pub trait Writable: RegisterSpec {
     type Safety;
 
     /// Specifies the register bits that are not changed if you pass `1` and are changed if you pass `0`
-    const ZERO_TO_MODIFY_FIELDS_BITMAP: Self::Ux;
+    const ZERO_TO_MODIFY_FIELDS_BITMAP: Self::Ux = Self::Ux::DEFAULT;
 
     /// Specifies the register bits that are not changed if you pass `0` and are changed if you pass `1`
-    const ONE_TO_MODIFY_FIELDS_BITMAP: Self::Ux;
+    const ONE_TO_MODIFY_FIELDS_BITMAP: Self::Ux = Self::Ux::DEFAULT;
 }
 
 /// Reset value of the register.
@@ -86,7 +87,7 @@ pub trait Writable: RegisterSpec {
 /// register by using the `reset` method.
 pub trait Resettable: RegisterSpec {
     /// Reset value of the register.
-    const RESET_VALUE: Self::Ux;
+    const RESET_VALUE: Self::Ux = Self::Ux::DEFAULT;
 
     /// Reset value of the register.
     #[inline(always)]
@@ -201,7 +202,7 @@ impl<REG: Writable> Reg<REG> {
     {
         self.register.set(
             f(&mut W {
-                bits: REG::Ux::default(),
+                bits: REG::Ux::DEFAULT,
                 _reg: marker::PhantomData,
             })
             .bits,

src/generate/generic_atomic.rs

@@ -39,7 +39,7 @@ mod atomic {
 
     impl<REG: Readable + Writable> Reg<REG>
     where
-        REG::Ux: AtomicOperations + Default + core::ops::Not<Output = REG::Ux>,
+        REG::Ux: AtomicOperations,
     {
         /// Set high every bit in the register that was set in the write proxy. Leave other bits
         /// untouched. The write is done in a single atomic instruction.
@@ -53,7 +53,7 @@ mod atomic {
             F: FnOnce(&mut W<REG>) -> &mut W<REG>,
         {
             let bits = f(&mut W {
-                bits: Default::default(),
+                bits: REG::Ux::DEFAULT,
                 _reg: marker::PhantomData,
             })
             .bits;
@@ -72,7 +72,7 @@ mod atomic {
             F: FnOnce(&mut W<REG>) -> &mut W<REG>,
         {
             let bits = f(&mut W {
-                bits: !REG::Ux::default(),
+                bits: !REG::Ux::DEFAULT,
                 _reg: marker::PhantomData,
             })
             .bits;
@@ -91,7 +91,7 @@ mod atomic {
             F: FnOnce(&mut W<REG>) -> &mut W<REG>,
         {
             let bits = f(&mut W {
-                bits: Default::default(),
+                bits: REG::Ux::DEFAULT,
                 _reg: marker::PhantomData,
             })
             .bits;

src/generate/register.rs

@@ -413,24 +413,31 @@ pub fn render_register_mod(
 
         let doc = format!("`write(|w| ..)` method takes [`{mod_ty}::W`](W) writer structure",);
 
-        let zero_to_modify_fields_bitmap = util::hex(zero_to_modify_fields_bitmap);
-        let one_to_modify_fields_bitmap = util::hex(one_to_modify_fields_bitmap);
+        let zero_to_modify_fields_bitmap = util::hex_nonzero(zero_to_modify_fields_bitmap)
+            .map(|bm| quote!(const ZERO_TO_MODIFY_FIELDS_BITMAP: #rty = #bm;));
+        let one_to_modify_fields_bitmap = util::hex_nonzero(one_to_modify_fields_bitmap)
+            .map(|bm| quote!(const ONE_TO_MODIFY_FIELDS_BITMAP: #rty = #bm;));
 
         mod_items.extend(quote! {
             #[doc = #doc]
             impl crate::Writable for #regspec_ty {
                 type Safety = crate::#safe_ty;
-                const ZERO_TO_MODIFY_FIELDS_BITMAP: #rty = #zero_to_modify_fields_bitmap;
-                const ONE_TO_MODIFY_FIELDS_BITMAP: #rty = #one_to_modify_fields_bitmap;
+                #zero_to_modify_fields_bitmap
+                #one_to_modify_fields_bitmap
             }
         });
     }
-    if let Some(rv) = properties.reset_value.map(util::hex) {
-        let doc = format!("`reset()` method sets {} to value {rv}", register.name);
+    if let Some(rv) = properties.reset_value.map(util::hex_nonzero) {
+        let doc = if let Some(rv) = &rv {
+            format!("`reset()` method sets {} to value {rv}", register.name)
+        } else {
+            format!("`reset()` method sets {} to value 0", register.name)
+        };
+        let rv = rv.map(|rv| quote!(const RESET_VALUE: #rty = #rv;));
         mod_items.extend(quote! {
             #[doc = #doc]
             impl crate::Resettable for #regspec_ty {
-                const RESET_VALUE: #rty = #rv;
+                #rv
             }
         });
     }

src/lib.rs

@@ -62,6 +62,7 @@
 //! - [`cortex-m`](https://crates.io/crates/cortex-m) >=v0.7.6
 //! - [`cortex-m-rt`](https://crates.io/crates/cortex-m-rt) >=v0.6.13
 //! - [`vcell`](https://crates.io/crates/vcell) >=v0.1.2
+//! - [`const-default`](https://crates.io/crates/const-default) >=v1.0
 //!
 //! Furthermore, the "device" feature of `cortex-m-rt` must be enabled when the `rt` feature
 //! is enabled. The `Cargo.toml` of the device crate will look like this:
@@ -126,6 +127,7 @@
 //! - [`msp430`](https://crates.io/crates/msp430) v0.4.x
 //! - [`msp430-rt`](https://crates.io/crates/msp430-rt) v0.4.x
 //! - [`vcell`](https://crates.io/crates/vcell) v0.1.x
+//! - [`const-default`](https://crates.io/crates/const-default) v1.x.x
 //!
 //! The "device" feature of `msp430-rt` must be enabled when the `rt` feature is
 //! enabled. The `Cargo.toml` of the device crate will look like this:
@@ -152,6 +154,7 @@
 //! - [`riscv`](https://crates.io/crates/riscv) v0.9.x (if target is RISC-V)
 //! - [`riscv-rt`](https://crates.io/crates/riscv-rt) v0.9.x (if target is RISC-V)
 //! - [`vcell`](https://crates.io/crates/vcell) v0.1.x
+//! - [`const-default`](https://crates.io/crates/const-default) v1.x.x
 //!
 //! The `*-rt` dependencies must be optional only enabled when the `rt` feature is enabled. The
 //! `Cargo.toml` of the device crate will look like this for a RISC-V target:
@@ -162,6 +165,7 @@
 //! riscv = "0.9.0"
 //! riscv-rt = { version = "0.9.0", optional = true }
 //! vcell = "0.1.0"
+//! const-default = "1.0"
 //!
 //! [features]
 //! rt = ["riscv-rt"]

src/util.rs

@@ -253,6 +253,11 @@ pub fn hex(n: u64) -> LitInt {
     )
 }
 
+/// Turns non-zero `n` into an unsuffixed separated hex token
+pub fn hex_nonzero(n: u64) -> Option<LitInt> {
+    (n != 0).then(|| hex(n))
+}
+
 /// Turns `n` into an unsuffixed token
 pub fn unsuffixed(n: impl Into<u64>) -> LitInt {
     LitInt::new(&n.into().to_string(), Span::call_site())