Merge pull request 'external-register' (#1) from external-register into master

Reviewed-on: https://code.bitgloo.com/clyne/funreg/pulls/1

1 files changed, 160 insertions, 68 deletions

diff --git a/funreg.hpp b/funreg.hpp
index 156b6cf..00cd3a9 100644
--- a/funreg.hpp
+++ b/funreg.hpp
@@ -1,5 +1,5 @@
 /**
- * funreg.hpp - Functional memory-mapped register I/O using modern C++.
+ * funreg.hpp - Functional register I/O using modern C++.
  * Written by Clyne Sullivan.
  * <https://github.com/tcsullivan/funreg>
  */
@@ -7,11 +7,22 @@
 #ifndef FUNCTIONAL_REGISTER_IO_H
 #define FUNCTIONAL_REGISTER_IO_H
 
+/**
+ * Comment to disable external/custom register access.
+ * When disabled, only memory-mapped register access is supported.
+ * fr::Register can then also be used instead of fr::MemRegister.
+ */
+#define FUNREG_ENABLE_EXTERNAL_IO
+
 #include <stdint.h>
 
+#ifdef FUNREG_ENABLE_EXTERNAL_IO
+#include <type_traits>
+#endif
+
 namespace fr {
 
-// A utility to measure a bit-mask's offset from bit zero. 
+// A utility to measure a bit-mask's offset from bit zero.
 template<auto Mask, unsigned int N = 0>
 constexpr auto BitOffset = []() constexpr {
     if constexpr (Mask & 1)
@@ -21,23 +32,66 @@ constexpr auto BitOffset = []() constexpr {
 }();
 
 /**
- * @struct Register
- * @brief  Defines a memory-mapped register, given bit-size and address.
- * @tparam T    The integer type that matches the size of the register.
+ * @struct MemoryIO
+ * @brief  Specifies how to access a memory-mapped register.
+ * @tparam T    The size of the register.
  * @tparam Addr The memory address of the register.
  *
- * Defines a memory-mapped register that is usually accessed with a pointer of
- * type T*, and is located at address Addr.
+ * To create an I/O access type for external register access, use this
+ * structure as a template.
+ */
+template<typename T, uintptr_t Addr>
+struct MemoryIO {
+    using type = T;
+    constexpr static auto addr = Addr;
+
+    /**
+     * Reads the register's value.
+     */
+    constexpr static T read() {
+        return *reinterpret_cast<volatile T*>(Addr);
+    }
+
+    /**
+     * Overwrites the register's value.
+     */
+    constexpr static void write(const T& value) {
+        *reinterpret_cast<volatile T*>(Addr) = value;
+    }
+};
+
+/**
+ * @struct Register
+ * @brief  Defines a register, given how to access it.
+ * @tparam Access Specifies register access. See MemoryIO for an example.
  *
- * Use only as a type, e.g. "using GPIO_OUT = Register<uint32_t, 0xA0004120>"
+ * When FUNREG_ENABLE_EXTERNAL_IO is not defined, Register assumes MemoryIO
+ * access. The template parameters become that of MemoryIO.
  */
+#ifdef FUNREG_ENABLE_EXTERNAL_IO
+template<typename Access>
+struct Register {
+    using access = Access;
+    using T = typename Access::type;
+    constexpr static auto Addr = Access::addr;
+#else
 template<typename T, uintptr_t Addr>
 struct Register {
+    using RegAccess = MemoryIO<T, Addr>;
+#endif // FUNREG_ENABLE_EXTERNAL_IO
+
     /**
      * Gets a pointer to the register.
      */
-    constexpr static auto get() {
-        return reinterpret_cast<volatile T*>(Addr);
+    constexpr static T read() {
+        return Access::read();
+    }
+
+    /**
+     * Overwrites the register's value.
+     */
+    constexpr static void write(const T& value) {
+        Access::write(value);
     }
 
     /**
@@ -45,14 +99,14 @@ struct Register {
      */
     template<typename... Masks>
     static void set() {
-        apply<Masks...>([](auto r, auto m) { *r = *r | m; });
+        apply<Masks...>([](auto r, auto m) { return r | m; });
     }
 
     /**
      * Sets register bits to '1' according to the given mask.
      */
     static void set(const T& mask) {
-        *get() = *get() | mask;
+        write(read() | mask);
     }
 
     /**
@@ -60,14 +114,14 @@ struct Register {
      */
     template<typename... Masks>
     static void clear() {
-        apply<Masks...>([](auto r, auto m) { *r = *r & ~m; });
+        apply<Masks...>([](auto r, auto m) { return r & ~m; });
     }
 
     /**
      * Clears register bits to '0' according to the given mask.
      */
     static void clear(const T& mask) {
-        *get() = *get() & ~mask;
+        write(read() & ~mask);
     }
 
     /**
@@ -75,14 +129,14 @@ struct Register {
      */
     template<typename... Masks>
     static void toggle() {
-        apply<Masks...>([](auto r, auto m) { *r = *r ^ m; });
+        apply<Masks...>([](auto r, auto m) { return r ^m; });
     }
 
     /**
      * Toggles bits in the register according to the given mask.
      */
     static void toggle(const T& mask) {
-        *get() = *get() ^ mask;
+        write(read() ^ mask);
     }
 
     /**
@@ -92,26 +146,10 @@ struct Register {
      */
     template<typename... Masks>
     static auto read() {
-        if constexpr (sizeof...(Masks) > 0) {
-            if (((Addr == Masks::reg::addr) | ...)) {
-                auto mask =
-                    ([] {
-                        return Addr == Masks::reg::addr ? Masks::mask : 0;
-                    }() | ...);
-                return *get() & mask;
-            } else {
-                return 0;
-            }
-        } else {
-            return *get();
-        }
-    }
-
-    /**
-     * Overwrites the entire register with the given value.
-     */
-    static void write(const T& value) {
-        *get() = value;
+        if constexpr (sizeof...(Masks) > 0)
+            return read() & mergeMasks<Masks...>();
+        else
+            return read();
     }
 
     /**
@@ -121,17 +159,10 @@ struct Register {
     template<typename... Masks>
     static bool test() {
         if constexpr (sizeof...(Masks) > 0) {
-            if (((Addr == Masks::reg::addr) | ...)) {
-                auto mask =
-                    ([] {
-                        return Addr == Masks::reg::addr ? Masks::mask : 0;
-                    }() | ...);
-                return (*get() & mask) == mask;
-            } else {
-                return 0;
-            }
+            auto mask = mergeMasks<Masks...>();
+            return (read() & mask) == mask;
         } else {
-            return *get() != 0;
+            return read() != 0;
         }
     }
 
@@ -144,17 +175,17 @@ struct Register {
      */
     template<typename... Ops>
     static void modify() {
-        if (((Addr == Ops::reg::addr) | ...)) {
-            auto mask = *get();
+        if constexpr ((isThis<typename Ops::reg> | ...)) {
+            auto mask = read();
             ([&mask] {
-                if (Addr == Ops::reg::addr)
+                if constexpr (isThis<typename Ops::reg>)
                     mask = Ops(mask);
             }(), ...);
-            *get() = mask;
+            write(mask);
         }
     }
 
-    // Below is meant for internal use only. 
+    // Below is meant for internal use only.
 
     // Applies bit-masks to the register through the provided function.
     // The provided function receives a pointer to the register's data and a
@@ -163,21 +194,50 @@ struct Register {
     template<typename... Masks>
     static void apply(auto fn) {
         if constexpr (sizeof...(Masks) > 0) {
-            auto mask =
+            auto mask = mergeMasks<Masks...>();
+            if constexpr (mask)
+                write(fn(read(), mask));
+        } else {
+            write(fn(read(), T(0) - 1));
+        }
+    }
+
+    // Takes a list of bit-masks, and returns a merged mask of those which are
+    // meant for this register.
+    template<typename... Masks>
+    static auto mergeMasks() {
+        if constexpr (sizeof...(Masks) > 0) {
+            if constexpr ((isThis<typename Masks::reg> | ...)) {
+                auto mask =
                     ([] {
-                        return Addr == Masks::reg::addr ? Masks::mask : 0;
+                        return isThis<typename Masks::reg> ? Masks::mask : 0;
                     }() | ...);
-            if (mask)
-                fn(get(), mask);
+                return mask;
+            } else {
+                return 0;
+            }
         } else {
-            fn(get(), T(0) - 1);
+            return 0;
         }
     }
 
+#ifdef FUNREG_ENABLE_EXTERNAL_IO
+    // Determines if the given register matches this one.
+    template<typename Reg>
+    constexpr static bool isThis = [] {
+        return std::is_same_v<typename Reg::access, access> && Addr == Reg::Addr;
+    }();
+#else
+    // Determines if the given register matches this one.
+    template<typename Reg>
+    constexpr static bool isThis = [] {
+        return Addr == Reg::Addr;
+    }();
+#endif // FUNREG_ENABLE_EXTERNAL_IO
+
     Register() = delete;
 
     using type = T;
-    constexpr static auto addr = Addr;
 };
 
 /**
@@ -203,7 +263,7 @@ struct RegisterMask
      */
     struct set {
         constexpr set() {
-            *Reg::get() = *Reg::get() | Mask;
+            Reg::write(Reg::read() | Mask);
         }
 
         // For internal use.
@@ -219,7 +279,7 @@ struct RegisterMask
      */
     struct clear {
         constexpr clear() {
-            *Reg::get() = *Reg::get() & ~Mask;
+            Reg::write(Reg::read() & ~Mask);
         }
 
         // For internal use.
@@ -235,7 +295,7 @@ struct RegisterMask
      */
     struct toggle {
         constexpr toggle() {
-            *Reg::get() = *Reg::get() ^ Mask;
+            Reg::write(Reg::read() ^ Mask);
         }
 
         // For internal use.
@@ -249,7 +309,7 @@ struct RegisterMask
      * Reads from the paired register, applying the bit-mask.
      */
     static auto read() {
-        return *Reg::get() & Mask;
+        return Reg::read() & Mask;
     }
 
     /**
@@ -272,10 +332,10 @@ struct RegisterMask
     template<T value>
     struct write {
         constexpr write() {
-            auto r = *Reg::get();
+            auto r = Reg::read();
             r &= ~Mask;
             r |= value << BitOffset<Mask>;
-            *Reg::get() = r;
+            Reg::write(r);
         }
 
         // For internal use.
@@ -332,7 +392,7 @@ struct RegisterMaskValue
      * Tests if this value is currently set in the register.
      */
     static bool test() {
-        return Mask::read() & (value << BitOffset<Mask>);
+        return (Mask::read() & Mask::mask) == (value << BitOffset<Mask>);
     }
 };
 
@@ -352,11 +412,11 @@ public:
     /**
      * Sets bits throughout this group's registers according to the given masks.
      * Bit-masks for the same register will be merged so that each register is
-     * only written once. 
+     * only written once.
      */
     template<typename... Masks>
     static void set() {
-        apply<Masks...>([](auto r, auto m) { *r = *r | m; });
+        apply<Masks...>([](auto r, auto m) { return r | m; });
     }
 
     /**
@@ -366,7 +426,7 @@ public:
      */
     template<typename... Masks>
     static void clear() {
-        apply<Masks...>([](auto r, auto m) { *r = *r & ~m; });
+        apply<Masks...>([](auto r, auto m) { return r & ~m; });
     }
 
     /**
@@ -376,7 +436,7 @@ public:
      */
     template<typename... Masks>
     static void toggle() {
-        apply<Masks...>([](auto r, auto m) { *r = *r ^ m; });
+        apply<Masks...>([](auto r, auto m) { return r ^ m; });
     }
 
     /**
@@ -407,6 +467,38 @@ private:
 template<typename... RegMasks>
 constexpr auto Masks = (RegMasks::mask | ...);
 
+#ifdef FUNREG_ENABLE_EXTERNAL_IO
+/**
+ * Defines a register that is accessed through memory, i.e. memory-mapped.
+ * @tparam T    The variable type used to access the register (e.g. uint32_t).
+ * @tparam Addr The memory address of the register.
+ */
+template<typename T, uintptr_t Addr>
+using MemRegister = Register<MemoryIO<T, Addr>>;
+
+/**
+ * Defines a register that is accessed through external or custom means.
+ * @tparam ExtIO A type that provides access functionality (e.g. MemoryIO).
+ * @tparam T     The variable type used to access the register (e.g. uint32_t).
+ * @tparam Addr  The memory address of the register.
+ *
+ * Custom access types should be defined using MemoryIO as a template.
+ */
+template<template<typename, uintptr_t> typename ExtIO, typename T, uintptr_t Addr>
+using ExtRegister = Register<ExtIO<T, Addr>>;
+#else
+/**
+ * Defines a register that is accessed through memory, i.e. memory-mapped.
+ * @tparam T    The variable type used to access the register (e.g. uint32_t).
+ * @tparam Addr The memory address of the register.
+ *
+ * With external I/O disabled, the Register type may be used directly instead.
+ */
+template<typename T, uintptr_t Addr>
+using MemRegister = Register<T, Addr>;
+#endif // FUNREG_ENABLE_EXTERNAL_IO
+
 } // namespace fr
 
 #endif // FUNCTIONAL_REGISTER_IO_H
+