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