From af06b4421c935040b1ad53a79586c95f0567ef68 Mon Sep 17 00:00:00 2001
From: Andrey Zgarbul <zgarbul.andrey@gmail.com>
Date: Sat, 18 Apr 2026 12:38:18 +0300
Subject: [PATCH] Reg::prepare

---
 CHANGELOG.md                      |  1 +
 src/generate/generic_reg_vcell.rs | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4d1e2974..c28580d5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
 - Use marker struct instead of address in `Periph` with `PeripheralSpec` trait
 - Add `--skip-peripherals-struct` flag to skip generating the `Peripherals`
   struct, its `take`/`steal` impl and the `DEVICE_PERIPHERALS` static
+- Add `Reg::prepare`.
 
 ## [v0.37.1] - 2025-10-17
 
diff --git a/src/generate/generic_reg_vcell.rs b/src/generate/generic_reg_vcell.rs
index 9e436334..2dd3aeeb 100644
--- a/src/generate/generic_reg_vcell.rs
+++ b/src/generate/generic_reg_vcell.rs
@@ -88,6 +88,20 @@ impl<REG: Resettable + Writable> Reg<REG> {
         value
     }
 
+    /// Prepare bits for delayed write to register.
+    #[inline(always)]
+    pub fn prepare<F>(&self, f: F) -> REG::Ux
+    where
+        F: FnOnce(&mut W<REG>) -> &mut W<REG>,
+    {
+        f(&mut W {
+            bits: REG::RESET_VALUE & !REG::ONE_TO_MODIFY_FIELDS_BITMAP
+                | REG::ZERO_TO_MODIFY_FIELDS_BITMAP,
+            _reg: marker::PhantomData,
+        })
+        .bits
+    }
+
     /// Writes bits to a `Writable` register and produce a value.
     ///
     /// You can write raw bits into a register: