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Remove Analog Driver chapter
There exists no standard Analog Driver in the RTEMS code base. Close #2850.
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Sebastian Huber
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.. comment SPDX-License-Identifier: CC-BY-SA-4.0
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.. COMMENT: COPYRIGHT (c) 1988-2002.
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.. COMMENT: On-Line Applications Research Corporation (OAR).
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.. COMMENT: All rights reserved.
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Analog Driver
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*************
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The Analog driver is responsible for providing an interface to Digital to
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Analog Converters (DACs) and Analog to Digital Converters (ADCs). The
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capabilities provided by this class of device driver are:
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- Initialize an Analog Board
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- Open a Particular Analog
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- Close a Particular Analog
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- Read from a Particular Analog
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- Write to a Particular Analog
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- Reset DACs
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- Reinitialize DACS
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Most analog devices are found on I/O cards that support multiple DACs or ADCs
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on a single card.
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There are currently no analog device drivers included in the RTEMS source tree.
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The information provided in this chapter is based on drivers developed for
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applications using RTEMS. It is hoped that this driver model information can
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form the basis for a standard analog driver model that can be supported in
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future RTEMS distribution.
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Major and Minor Numbers
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=======================
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The ``major`` number of a device driver is its index in the RTEMS Device
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Address Table.
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A ``minor`` number is associated with each device instance managed by a
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particular device driver. An RTEMS minor number is an ``unsigned32`` entity.
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Convention calls for dividing the bits in the minor number down into categories
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like the following:
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- ``board`` - indicates the board a particular device is located on
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- ``port`` - indicates the particular device on a board.
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From the above, it should be clear that a single device driver can support
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multiple copies of the same board in a single system. The minor number is used
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to distinguish the devices.
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Analog Driver Configuration
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===========================
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There is not a standard analog driver configuration table but some fields are
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common across different drivers. The analog driver configuration table is
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typically an array of structures with each structure containing the information
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for a particular board. The following is a list of the type of information
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normally required to configure an analog board:
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``board_offset``
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is the base address of a board.
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``DAC_initial_values``
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is an array of the voltages that should be written to each DAC during
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initialization. This allows the driver to start the board in a known
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state.
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Initialize an Analog Board
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==========================
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At system initialization, the analog driver's initialization entry point will
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be invoked. As part of initialization, the driver will perform whatever board
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initialization is required and then set all outputs to their configured initial
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state.
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The analog driver may register a device name for each DAC and ADC in the
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system.
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Open a Particular Analog
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========================
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This is the driver open call. Usually this call does nothing other than
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validate the minor number.
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With some drivers, it may be necessary to allocate memory when a particular
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device is opened. If that is the case, then this is often the place to do this
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operation.
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Close a Particular Analog
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=========================
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This is the driver close call. Usually this call does nothing.
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With some drivers, it may be necessary to allocate memory when a particular
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device is opened. If that is the case, then this is the place where that
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memory should be deallocated.
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Read from a Particular Analog
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=============================
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This corresponds to the driver read call. After validating the minor number
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and arguments, this call reads the indicated device. Most analog devices store
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the last value written to a DAC. Since DACs are output only devices, saving
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the last written value gives the appearance that DACs can be read from also.
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If the device is an ADC, then it is sampled.
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.. note::
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Many boards have multiple analog inputs but only one ADC. On these boards,
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it will be necessary to provide some type of mutual exclusion during reads.
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On these boards, there is a MUX which must be switched before sampling the
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ADC. After the MUX is switched, the driver must delay some short period of
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time (usually microseconds) before the signal is stable and can be sampled.
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To make matters worse, some ADCs cannot respond to wide voltage swings in a
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single sample. On these ADCs, one must do two samples when the voltage
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swing is too large. On a practical basis, this means that the driver
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usually ends up double sampling the ADC on these systems.
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The value returned is a single precision floating point number representing the
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voltage read. This value is stored in the ``argument_block`` passed in to the
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call. By returning the voltage, the caller is freed from having to know the
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number of bits in the analog and board dependent conversion algorithm.
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Write to a Particular Analog
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============================
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This corresponds to the driver write call. After validating the minor number
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and arguments, this call writes the indicated device. If the specified device
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is an ADC, then an error is usually returned.
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The value written is a single precision floating point number representing the
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voltage to be written to the specified DAC. This value is stored in the
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``argument_block`` passed in to the call. By passing the voltage to the device
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driver, the caller is freed from having to know the number of bits in the
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analog and board dependent conversion algorithm.
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Reset DACs
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==========
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This is one of the IOCTL functions supported by the I/O control device driver
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entry point. When this IOCTL function is invoked, all of the DACs are written
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to 0.0 volts.
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Reinitialize DACS
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=================
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This is one of the IOCTL functions supported by the I/O control device driver
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entry point. When this IOCTL function is invoked, all of the DACs are written
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with the initial value configured for this device.
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Get Last Written Values
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=======================
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This is one of the IOCTL functions supported by the I/O control device driver
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entry point. When this IOCTL function is invoked, the following information is
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returned to the caller:
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- last value written to the specified DAC
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- timestamp of when the last write was performed
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@ -57,7 +57,6 @@ to the Community Project hosted at http://www.rtems.org.
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networking
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networking
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shared_memory_support
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shared_memory_support
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frame_buffer
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frame_buffer
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analog
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discrete
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discrete
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command
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command
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