Merge #365

365: fix docs+examples, work without reset, fixes r=therealprof a=burrbull

r? @therealprof 

Add more docs as @Disasm proposed.

Restore `unsafe` on `W::bits()` I somewhere lost.

Don't generate `write` if `reset_value` is not present. #258 

Co-authored-by: Andrey Zgarbul <zgarbul.andrey@gmail.com>

Author: bors[bot]

CHANGELOG.md

@@ -11,11 +11,17 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - `variant()` method for field reader and `Variant` enum for fields with reserved values
 
+- Update documentation, add examples for register access methods
+
+- Add `write_with_zero` method for registers without reset value
+
 ### Changed
 
-  - Field readers and writers use one enum where it is possible
+- Field readers and writers use one enum where it is possible
+
+- Replace register and its reader/writer by generic types
 
-  - Replace register and its reader/writer by generic types
+- Restore `unsafe` marker on register writer `bits()` method
 
 ## [v0.15.2] - 2019-07-29
 

src/generate/generic.rs

@@ -42,7 +42,16 @@ where
 {
     ///Reads the contents of `Readable` register
     ///
-    ///See [reading](https://rust-embedded.github.io/book/start/registers.html#reading) in book.
+    ///You can read the contents of a register in such way:
+    ///```ignore
+    ///let bits = periph.reg.read().bits();
+    ///```
+    ///or get the content of a particular field of a register.
+    ///```ignore
+    ///let reader = periph.reg.read();
+    ///let bits = reader.field1().bits();
+    ///let flag = reader.field2().bit_is_set();
+    ///```
     #[inline(always)]
     pub fn read(&self) -> R<U, Self> {
         R {bits: self.register.get(), _reg: marker::PhantomData}
@@ -55,6 +64,8 @@ where
     U: Copy,
 {
     ///Writes the reset value to `Writable` register
+    ///
+    ///Resets the register to its initial state
     #[inline(always)]
     pub fn reset(&self) {
         self.register.set(Self::reset_value())
@@ -68,7 +79,19 @@ where
 {
     ///Writes bits to `Writable` register
     ///
-    ///See [writing](https://rust-embedded.github.io/book/start/registers.html#writing) in book.
+    ///You can write raw bits into a register:
+    ///```ignore
+    ///periph.reg.write(|w| unsafe { w.bits(rawbits) });
+    ///```
+    ///or write only the fields you need:
+    ///```ignore
+    ///periph.reg.write(|w| w
+    ///    .field1().bits(newfield1bits)
+    ///    .field2().set_bit()
+    ///    .field3().variant(VARIANT)
+    ///);
+    ///```
+    ///Other fields will have reset value.
     #[inline(always)]
     pub fn write<F>(&self, f: F)
     where
@@ -84,6 +107,8 @@ where
     U: Copy + Default
 {
     ///Writes Zero to `Writable` register
+    ///
+    ///Similar to `write`, but unused bits will contain 0.
     #[inline(always)]
     pub fn write_with_zero<F>(&self, f: F)
     where
@@ -100,7 +125,21 @@ where
 {
     ///Modifies the contents of the register
     ///
-    ///See [modifying](https://rust-embedded.github.io/book/start/registers.html#modifying) in book.
+    ///E.g. to do a read-modify-write sequence to change parts of a register:
+    ///```ignore
+    ///periph.reg.modify(|r, w| unsafe { w.bits(
+    ///   r.bits() | 3
+    ///) });
+    ///```
+    ///or
+    ///```ignore
+    ///periph.reg.modify(|_, w| w
+    ///    .field1().bits(newfield1bits)
+    ///    .field2().set_bit()
+    ///    .field3().variant(VARIANT)
+    ///);
+    ///```
+    ///Other fields will have value they had before call `modify`.
     #[inline(always)]
     pub fn modify<F>(&self, f: F)
     where
@@ -112,6 +151,9 @@ where
 }
 
 ///Register/field reader
+///
+///Result of the [`read`](Reg::read) method of a register.
+///Also it can be used in the [`modify`](Reg::read) method
 pub struct R<U, T> {
     pub(crate) bits: U,
     _reg: marker::PhantomData<T>,
@@ -141,6 +183,7 @@ where
     U: PartialEq,
     FI: ToBits<U>
 {
+    #[inline(always)]
     fn eq(&self, other: &FI) -> bool {
         self.bits.eq(&other._bits())
     }
@@ -165,16 +208,18 @@ impl<FI> R<bool, FI> {
 }
 
 ///Register writer
+///
+///Used as an argument to the closures in the [`write`](Reg::write) and [`modify`](Reg::modify) methods of the register
 pub struct W<U, REG> {
     ///Writable bits
-    pub bits: U,
+    pub(crate) bits: U,
     _reg: marker::PhantomData<REG>,
 }
 
 impl<U, REG> W<U, REG> {
     ///Writes raw bits to the register
     #[inline(always)]
-    pub fn bits(&mut self, bits: U) -> &mut Self {
+    pub unsafe fn bits(&mut self, bits: U) -> &mut Self {
         self.bits = bits;
         self
     }

src/generate/register.rs

@@ -54,26 +54,28 @@ pub fn render(
     }
 
     if can_write {
-        let rv = register
-            .reset_value
-            .or(defs.reset_value)
-            .map(|v| util::hex(v as u64))
-            .ok_or_else(|| format!("Register {} has no reset value", register.name))?;
-
         let desc = format!("Writer for register {}", register.name);
-        let doc = format!("Register {} `reset()`'s with value {}", register.name, &rv);
         mod_items.push(quote! {
             #[doc = #desc]
             pub type W = crate::W<#rty, super::#name_pc>;
-            #[doc = #doc]
-            impl crate::ResetValue for super::#name_pc {
-                type Type = #rty;
-                #[inline(always)]
-                fn reset_value() -> Self::Type { #rv }
-            }
         });
-        methods.push("reset");
-        methods.push("write");
+        let res_val = register
+            .reset_value
+            .or(defs.reset_value)
+            .map(|v| util::hex(v as u64));
+        if let Some(rv) = res_val {
+            let doc = format!("Register {} `reset()`'s with value {}", register.name, &rv);
+            mod_items.push(quote! {
+                #[doc = #doc]
+                impl crate::ResetValue for super::#name_pc {
+                    type Type = #rty;
+                    #[inline(always)]
+                    fn reset_value() -> Self::Type { #rv }
+                }
+            });
+            methods.push("reset");
+            methods.push("write");
+        }
         methods.push("write_with_zero");
     }
 

src/lib.rs

@@ -226,8 +226,14 @@
 //!         ..
 //!     }
 //! }
+//! impl crate::ResetValue for CR2 {
+//!     type Type = u32;
+//!     fn reset_value() -> Self::Type { 0 }
+//! }
 //! ```
 //!
+//! ## `read`
+//!
 //! The `read` method "reads" the register using a **single**, volatile `LDR` instruction and
 //! returns a proxy `R` struct that allows access to only the readable bits (i.e. not to the
 //! reserved or write-only bits) of the `CR2` register:
@@ -236,10 +242,10 @@
 //! /// Value read from the register
 //! impl R {
 //!     /// Bit 0 - Slave address bit 0 (master mode)
-//!     pub fn sadd0(&self) -> SADD0R { .. }
+//!     pub fn sadd0(&self) -> SADD0_R { .. }
 //!
 //!     /// Bits 1:7 - Slave address bit 7:1 (master mode)
-//!     pub fn sadd1(&self) -> SADD1R { .. }
+//!     pub fn sadd1(&self) -> SADD1_R { .. }
 //!
 //!     (..)
 //! }
@@ -256,26 +262,30 @@
 //! }
 //! ```
 //!
+//! ## `reset`
+//!
+//! The `ResetValue` trait provides `reset_value` which returns the value of the `CR2`
+//! register after a reset. This value can be used to modify the
+//! writable bitfields of the `CR2` register or reset it to its initial state.
+//! Usage looks like this:
+//!
+//! ```ignore
+//! if i2c1.c2r.write().reset()
+//! ```
+//!
+//! ## `write`
+//!
 //! On the other hand, the `write` method writes some value to the register using a **single**,
 //! volatile `STR` instruction. This method involves a `W` struct that only allows constructing
 //! valid states of the `CR2` register.
 //!
-//! The only constructor that `W` provides is `reset_value` which returns the value of the `CR2`
-//! register after a reset. The rest of `W` methods are "builder-like" and can be used to modify the
-//! writable bitfields of the `CR2` register.
-//!
 //! ```ignore
-//! impl CR2W {
-//!     /// Reset value
-//!     pub fn reset_value() -> Self {
-//!         CR2W { bits: 0 }
-//!     }
-//!
+//! impl W {
 //!     /// Bits 1:7 - Slave address bit 7:1 (master mode)
-//!     pub fn sadd1(&mut self) -> _SADD1W { .. }
+//!     pub fn sadd1(&mut self) -> SADD1_W { .. }
 //!
 //!     /// Bit 0 - Slave address bit 0 (master mode)
-//!     pub fn sadd0(&mut self) -> SADD0R { .. }
+//!     pub fn sadd0(&mut self) -> SADD0_W { .. }
 //! }
 //! ```
 //!
@@ -300,6 +310,8 @@
 //! // field; instead, `6 & 3` (i.e. `2`) will be written to the bitfield.
 //! ```
 //!
+//! ## `modify`
+//!
 //! Finally, the `modify` method performs a **single** read-modify-write
 //! operation that involves **one** read (`LDR`) to the register, modifying the
 //! value and then a **single** write (`STR`) of the modified value to the
@@ -327,16 +339,16 @@
 //! The new `read` API returns an enum that you can match:
 //!
 //! ```ignore
-//! match gpioa.dir.read().pin0() {
-//!     gpioa::dir::PIN0R::Input => { .. },
-//!     gpioa::dir::PIN0R::Output => { .. },
+//! match gpioa.dir.read().pin0().variant() {
+//!     gpioa::dir::PIN0_A::Input => { .. },
+//!     gpioa::dir::PIN0_A::Output => { .. },
 //! }
 //! ```
 //!
 //! or test for equality
 //!
 //! ```ignore
-//! if gpioa.dir.read().pin0() == gpio::dir::PIN0R::Input {
+//! if gpioa.dir.read().pin0().variant() == gpio::dir::PIN0_A::Input {
 //!     ..
 //! }
 //! ```
@@ -366,8 +378,8 @@
 //! write from an `enum`eration of the possible ones:
 //!
 //! ```ignore
-//! // enum DIRW { Input, Output }
-//! gpioa.dir.write(|w| w.pin0().variant(gpio::dir::PIN0W::Output));
+//! // enum PIN0_A { Input, Output }
+//! gpioa.dir.write(|w| w.pin0().variant(gpio::dir::PIN0_A::Output));
 //! ```
 //!
 //! There are convenience methods to pick one of the variants without having to