2010-10-25 18:48:13 +00:00
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/*
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ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio.
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This file is part of ChibiOS/RT.
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ChibiOS/RT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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ChibiOS/RT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* @defgroup PAL PAL Driver
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* @brief I/O Ports Abstraction Layer
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* @details This module defines an abstract interface for digital I/O ports.
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* Note that most I/O ports functions are just macros. The macros
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* have default software implementations that can be redefined in a
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* PAL Low Level Driver if the target hardware supports special features like,
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* as example, atomic bit set/reset/masking. Please refer to the ports specific
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* documentation for details.<br>
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* The @ref PAL has the advantage to make the access to the I/O ports platform
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* independent and still be optimized for the specific architectures.<br>
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* Note that the PAL Low Level Driver may also offer non standard macro and
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* functions in order to support specific features but, of course, the use of
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* such interfaces would not be portable. Such interfaces shall be marked with
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* the architecture name inside the function names.
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2011-01-09 13:33:20 +00:00
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* @pre In order to use the PAL driver the @p HAL_USE_PAL option
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2010-10-25 18:48:13 +00:00
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* must be enabled in @p halconf.h.
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*
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* @section pal_1 Implementation Rules
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* In implementing a PAL Low Level Driver there are some rules/behaviors that
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* should be respected.
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*
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* @subsection pal_1_1 Writing on input pads
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* The behavior is not specified but there are implementations better than
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* others, this is the list of possible implementations, preferred options
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* are on top:
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* -# The written value is not actually output but latched, should the pads
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* be reprogrammed as outputs the value would be in effect.
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* -# The write operation is ignored.
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* -# The write operation has side effects, as example disabling/enabling
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* pull up/down resistors or changing the pad direction. This scenario is
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* discouraged, please try to avoid this scenario.
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* .
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* @subsection pal_1_2 Reading from output pads
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* The behavior is not specified but there are implementations better than
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* others, this is the list of possible implementations, preferred options
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* are on top:
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* -# The actual pads states are read (not the output latch).
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* -# The output latch value is read (regardless of the actual pads states).
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* -# Unspecified, please try to avoid this scenario.
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* .
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* @subsection pal_1_3 Writing unused or unimplemented port bits
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* The behavior is not specified.
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*
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* @subsection pal_1_4 Reading from unused or unimplemented port bits
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* The behavior is not specified.
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*
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* @subsection pal_1_5 Reading or writing on pins associated to other functionalities
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* The behavior is not specified.
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*
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* @ingroup IO
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*/
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