Expose the orphaned ICTR/ACTLR registers.

In ARMv7-M these were floating alone in system control space, without a
unifying name. As a result, they weren't exposed in earlier versions of
this crate.

In ARMv8-M they have been given a name, the Implementation Control
Block, and more registers have been added. I've used that name for all
architecture revisions.

Author: cbiffle

src/peripheral/icb.rs

@@ -0,0 +1,30 @@
+//! Implementation Control Block
+
+use volatile_register::{RO, RW};
+
+/// Register block
+#[repr(C)]
+pub struct RegisterBlock {
+    /// Interrupt Controller Type Register
+    ///
+    /// The bottom four bits of this register give the number of implemented
+    /// interrupt lines, divided by 32. So a value of `0b0010` indicates 64
+    /// interrupts.
+    #[cfg(any(armv7m, armv8m, target_arch = "x86_64"))]
+    pub ictr: RO<u32>,
+
+    /// The ICTR is not defined in the ARMv6-M Architecture Reference manual, so
+    /// we replace it with this.
+    #[cfg(not(any(armv7m, armv8m, target_arch = "x86_64")))]
+    _reserved: u32,
+
+    /// Auxiliary Control Register
+    ///
+    /// This register is entirely implementation defined -- the standard gives
+    /// it an address, but does not define its role or contents.
+    pub actlr: RW<u32>,
+
+    /// Coprocessor Power Control Register
+    #[cfg(armv8m)]
+    pub cppwr: RW<u32>,
+}

src/peripheral/mod.rs

@@ -68,7 +68,7 @@
 //!
 //! - ARMv7-M Architecture Reference Manual (Issue E.b) - Chapter B3
 
-// TODO stand-alone registers: ICTR, ACTLR and STIR
+// TODO stand-alone register: STIR
 
 
 use core::marker::PhantomData;
@@ -86,6 +86,7 @@ pub mod fpb;
 // NOTE(target_arch) is for documentation purposes
 #[cfg(any(has_fpu, target_arch = "x86_64"))]
 pub mod fpu;
+pub mod icb;
 #[cfg(not(armv6m))]
 pub mod itm;
 pub mod mpu;
@@ -122,7 +123,14 @@ pub struct Peripherals {
     /// Floating Point Unit (only present on `thumbv7em-none-eabihf`)
     pub FPU: FPU,
 
-    /// Instrumentation Trace Macrocell (not present on Cortex-M0 variants)
+    /// Implementation Control Block.
+    ///
+    /// The name is from the v8-M spec, but the block existed in earlier
+    /// revisions, without a name.
+    pub ICB: ICB,
+
+    /// Instrumentation Trace Macrocell.
+    /// Not available on Armv6-M and Armv8-M Baseline.
     pub ITM: ITM,
 
     /// Memory Protection Unit
@@ -183,6 +191,9 @@ impl Peripherals {
             FPU: FPU {
                 _marker: PhantomData,
             },
+            ICB: ICB {
+                _marker: PhantomData,
+            },
             ITM: ITM {
                 _marker: PhantomData,
             },
@@ -362,6 +373,42 @@ impl ops::Deref for FPU {
     }
 }
 
+/// Implementation Control Block.
+///
+/// This block contains implementation-defined registers like `ictr` and
+/// `actlr`. It's called the "implementation control block" in the ARMv8-M
+/// standard, but earlier standards contained the registers, just without a
+/// name.
+pub struct ICB {
+    _marker: PhantomData<*const ()>,
+}
+
+unsafe impl Send for ICB {}
+
+impl ICB {
+    /// Returns a pointer to the register block
+    #[inline(always)]
+    pub fn ptr() -> *mut icb::RegisterBlock {
+        0xE000_E004 as *mut _
+    }
+}
+
+impl ops::Deref for ICB {
+    type Target = self::icb::RegisterBlock;
+
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*Self::ptr() }
+    }
+}
+
+impl ops::DerefMut for ICB {
+    #[inline(always)]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { &mut *Self::ptr() }
+    }
+}
+
 /// Instrumentation Trace Macrocell
 pub struct ITM {
     _marker: PhantomData<*const ()>,