genode/base/include/drivers/timer/epit_base.h

/*
 * \brief  Driver base for the Enhanced Periodic Interrupt Timer (Freescale)
 * \author Norman Feske
 * \author Martin Stein
 * \author Stefan Kalkowski
 * \date   2012-10-25
 */

/*
 * Copyright (C) 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 _INCLUDE__DRIVERS__TIMER__EPIT_BASE_H_
#define _INCLUDE__DRIVERS__TIMER__EPIT_BASE_H_

/* Genode includes */
#include <util/mmio.h>

namespace Genode
{
	/**
	 * Core timer
	 */
	class Epit_base : public Mmio
	{
		protected:

			enum { TICS_PER_MS = 32 };

			/**
			 * Control register
			 */
			struct Cr : Register<0x0, 32>
			{
				struct En : Bitfield<0, 1> { };       /* enable timer */

				struct En_mod : Bitfield<1, 1>        /* reload on enable */
				{
					enum { RELOAD = 1 };
				};

				struct Oci_en : Bitfield<2, 1> { };   /* interrupt on compare */

				struct Rld : Bitfield<3, 1>           /* reload or roll-over */
				{
					enum { RELOAD_FROM_LR = 1 };
				};

				struct Prescaler : Bitfield<4, 12>    /* clock input divisor */
				{
					enum { DIVIDE_BY_1 = 0 };
				};

				struct Swr     : Bitfield<16, 1> { }; /* software reset bit */
				struct Iovw    : Bitfield<17, 1> { }; /* enable overwrite */
				struct Dbg_en  : Bitfield<18, 1> { }; /* enable in debug mode */
				struct Wait_en : Bitfield<19, 1> { }; /* enable in wait mode */
				struct Doz_en  : Bitfield<20, 1> { }; /* enable in doze mode */
				struct Stop_en : Bitfield<21, 1> { }; /* enable in stop mode */

				struct Om : Bitfield<22, 2>           /* mode of the output pin */
				{
					enum { DISCONNECTED = 0 };
				};

				struct Clk_src : Bitfield<24, 2>      /* select clock input */
				{
					enum { IPG_CLK_32K = 3 };
				};

				/**
				 * Register value that configures the timer for a one-shot run
				 */
				static access_t prepare_one_shot()
				{
					return En::bits(0) |
					       En_mod::bits(En_mod::RELOAD) |
					       Oci_en::bits(1) |
					       Rld::bits(Rld::RELOAD_FROM_LR) |
					       Prescaler::bits(Prescaler::DIVIDE_BY_1) |
					       Swr::bits(0) |
					       Iovw::bits(0) |
					       Dbg_en::bits(0) |
					       Wait_en::bits(0) |
					       Doz_en::bits(0) |
					       Stop_en::bits(0) |
					       Om::bits(Om::DISCONNECTED) |
					       Clk_src::bits(Clk_src::IPG_CLK_32K);
				}
			};

			/**
			 * Status register
			 */
			struct Sr : Register<0x4, 32>
			{
				struct Ocif : Bitfield<0, 1> { }; /* IRQ status, write 1 clears */
			};

			struct Lr   : Register<0x8,  32> { }; /* load value register */
			struct Cmpr : Register<0xc,  32> { }; /* compare value register */
			struct Cnt  : Register<0x10, 32> { }; /* counter register */

			/**
			 * Disable timer and clear its interrupt output
			 */
			void _reset()
			{
				/* wait until ongoing reset operations are finished */
				while (read<Cr::Swr>()) ;

				/* disable timer */
				write<Cr::En>(0);
				clear_interrupt();
			}

		public:

			/**
			 * Constructor
			 */
			Epit_base(addr_t base) : Mmio(base) { _reset(); }

			/**
			 * Start a one-shot run
			 *
			 * \param tics  native timer value used to assess the delay
			 *              of the timer interrupt as of the call
			 */
			void start_one_shot(unsigned const tics)
			{
				/* stop timer */
				_reset();

				/* configure timer for a one-shot */
				write<Cr>(Cr::prepare_one_shot());
				write<Lr>(tics);
				write<Cmpr>(0);

				/* start timer */
				write<Cr::En>(1);
			}

			/**
			 * Stop the timer from a one-shot run
			 *
			 * \return  last native timer value of the one-shot run
			 */
			unsigned long stop_one_shot()
			{
				/* disable timer */
				write<Cr::En>(0);

				/* if the timer has hit zero already return 0 */
				return read<Sr::Ocif>() ? 0 : read<Cnt>();
			}

			/**
			 * Clear interrupt output line
			 */
			void clear_interrupt() { write<Sr::Ocif>(1); }

			/**
			 * Translate milliseconds to a native timer value
			 */
			static unsigned ms_to_tics(unsigned const ms) {
				return TICS_PER_MS * ms; }
	};
}

#endif /* _INCLUDE__DRIVERS__TIMER__EPIT_BASE_H_ */