71 lines
3.2 KiB
Plaintext
71 lines
3.2 KiB
Plaintext
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/*
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ChibiOS - Copyright (C) 2006..2018 Giovanni Di Sirio
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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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
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* features like, for example, atomic bit set/reset/masking. Please
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* refer to the ports specific documentation for details.<br>
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* The @ref PAL driver has the advantage to make the access to the I/O
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* ports platform independent and still be optimized for the specific
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* architectures.<br>
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* Note that the PAL Low Level Driver may also offer non standard
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* macro and functions in order to support specific features but,
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* of course, the use of such interfaces would not be portable.
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* Such interfaces shall be marked with the architecture name inside
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* the function names.
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* @pre In order to use the PAL driver the @p HAL_USE_PAL option
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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 HAL_NORMAL_DRIVERS
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*/
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