genode/base/include/util/register.h

/*
 * \brief  Generic accessor framework for highly structured memory regions
 * \author Martin stein
 * \date   2011-11-10
 */

/*
 * Copyright (C) 2011-2012 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU General Public License version 2.
 */

#ifndef _BASE__INCLUDE__UTIL__REGISTER_H_
#define _BASE__INCLUDE__UTIL__REGISTER_H_

#include <base/stdint.h>

namespace Genode
{
	namespace Trait {

		/**
		 * Properties of integer types with a given bitwidth
		 */
		template <unsigned long _WIDTH> struct Uint_type;

		/***************************************************************
		 ** Provide the integer type and the width as exponent to the **
		 ** base of 2 for all supported widths in 'Uint_type'         **
		 ***************************************************************/

		template <> struct Uint_type<8>
		{
			typedef uint8_t Type;
			enum { WIDTH_LOG2 = 3 };

			/**
			 * Access widths, wich are dividers to the compound type width
			 */
			template <unsigned long _DIVISOR_WIDTH> struct Divisor;
		};

		template <> struct Uint_type<16> : Uint_type<8>
		{
			typedef uint16_t Type;
			enum { WIDTH_LOG2 = 4 };
		};

		template <> struct Uint_type<32> : Uint_type<16>
		{
			typedef uint32_t Type;
			enum { WIDTH_LOG2 = 5 };
		};

		template <> struct Uint_type<64> : Uint_type<32>
		{
			typedef uint32_t Type;
			enum { WIDTH_LOG2 = 6 };
		};


		/********************************************************************
		 ** Provide widths as exponents to the base of 2 for all supported **
		 ** access widths in 'Uint_type::Divisor'                          **
		 ********************************************************************/

		template <> struct Uint_type<8>::Divisor<1> { enum { WIDTH_LOG2 = 0 }; };
		template <> struct Uint_type<8>::Divisor<2> { enum { WIDTH_LOG2 = 1 }; };
		template <> struct Uint_type<8>::Divisor<4> { enum { WIDTH_LOG2 = 2 }; };
		template <> struct Uint_type<8>::Divisor<8> { enum { WIDTH_LOG2 = 3 }; };
		template <> struct Uint_type<16>::Divisor<16> { enum { WIDTH_LOG2 = 4 }; };
		template <> struct Uint_type<32>::Divisor<32> { enum { WIDTH_LOG2 = 5 }; };
		template <> struct Uint_type<64>::Divisor<64> { enum { WIDTH_LOG2 = 6 }; };
	}

	/**
	 * An integer like highly structured memory region
	 *
	 * \param  _ACCESS_WIDTH  Bit width of the region
	 *
	 * The register can contain multiple bitfields. Bitfields that are
	 * partially exceed the register range are read and written also partially.
	 * Bitfields that are completely out of the register range are read as '0'
	 * and trying to overwrite them has no effect.
	 */
	template <unsigned long _ACCESS_WIDTH>
	struct Register
	{
		enum {
			ACCESS_WIDTH      = _ACCESS_WIDTH,

			ACCESS_WIDTH_LOG2 = Trait::Uint_type<ACCESS_WIDTH>::WIDTH_LOG2,
		};

		typedef typename Trait::Uint_type<ACCESS_WIDTH>::Type access_t;

		/**
		 * A bitregion within a register
		 *
		 * \param  _SHIFT  Bit shift of the first bit within the compound
		 *                 register
		 * \param  _WIDTH  Bit width of the region
		 *
		 * \detail  Bitfields are read and written according to their range,
		 *          so if we have a 'Bitfield<2,3>' and write '0b11101' to it
		 *          only '0b101' (shiftet by 2 bits) is written
		 */
		template <unsigned long _SHIFT, unsigned long _WIDTH>
		struct Bitfield
		{
			enum {

				/**
				 * Fetch template parameters
				 */
				SHIFT      = _SHIFT,
				WIDTH      = _WIDTH,

				MASK       = (1 << WIDTH) - 1,
				REG_MASK   = MASK << SHIFT,
				CLEAR_MASK = ~REG_MASK,
			};

			/**
			 * Back reference to containing register
			 */
			typedef Register<ACCESS_WIDTH> Compound_reg;

			/**
			 * Get a register value with this bitfield set to 'value' and the
			 * rest left zero
			 *
			 * \detail  Useful to combine successive access to multiple
			 *          bitfields into one operation
			 */
			static inline access_t bits(access_t const value) {
				return (value & MASK) << SHIFT; }

			/**
			 * Get value of this bitfield from 'reg'
			 */
			static inline access_t get(access_t const reg) {
				return (reg >> SHIFT) & MASK; }

			/**
			 * Get registervalue 'reg' with this bitfield set to zero
			 */
			static inline void clear(access_t & reg) { reg &= CLEAR_MASK; }

			/**
			 * Get registervalue 'reg' with this bitfield set to 'value'
			 */
			static inline void set(access_t & reg, access_t const value = ~0)
			{
				clear(reg);
				reg |= (value & MASK) << SHIFT;
			};
		};
	};
}

#endif /* _BASE__INCLUDE__UTIL__REGISTER_H_ */