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diff --git a/bsp_howto/analog.rst b/bsp_howto/analog.rst index 1548681..ac8ddb0 100644 --- a/bsp_howto/analog.rst +++ b/bsp_howto/analog.rst @@ -1,12 +1,15 @@ .. comment SPDX-License-Identifier: CC-BY-SA-4.0 +.. COMMENT: COPYRIGHT (c) 1988-2002. +.. COMMENT: On-Line Applications Research Corporation (OAR). +.. COMMENT: All rights reserved. + 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: +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 @@ -22,64 +25,61 @@ by this class of device driver are: - Reinitialize DACS -Most analog devices are found on I/O cards that support multiple -DACs or ADCs on a single card. +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. +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. +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 +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 +- ``board`` - indicates the board a particular device is located on -- *port* - indicates the particular device on a board. +- ``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. +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: +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* +``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. +``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. +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. +The analog driver may register a device name for each DAC and ADC in the +system. Open a Particular Analog ======================== @@ -88,8 +88,8 @@ 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. +device is opened. If that is the case, then this is often the place to do this +operation. Close a Particular Analog ========================= @@ -97,77 +97,69 @@ 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. +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. +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. +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. +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. +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. +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: +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. - |