From b35050917272ab536c8f4158e5c002f98a092796 Mon Sep 17 00:00:00 2001 From: Amar Takhar Date: Sun, 17 Jan 2016 00:47:50 -0500 Subject: Split document into seperate files by section. --- bsp_howto/discrete.rst | 187 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 187 insertions(+) create mode 100644 bsp_howto/discrete.rst (limited to 'bsp_howto/discrete.rst') diff --git a/bsp_howto/discrete.rst b/bsp_howto/discrete.rst new file mode 100644 index 0000000..c5ce450 --- /dev/null +++ b/bsp_howto/discrete.rst @@ -0,0 +1,187 @@ +Discrete Driver +############### + +The Discrete driver is responsible for providing an +interface to Discrete Input/Outputs. The capabilities provided +by this class of device driver are: + +- Initialize a Discrete I/O Board + +- Open a Particular Discrete Bitfield + +- Close a Particular Discrete Bitfield + +- Read from a Particular Discrete Bitfield + +- Write to a Particular Discrete Bitfield + +- Reset DACs + +- Reinitialize DACS + +Most discrete I/O devices are found on I/O cards that support many +bits of discrete I/O on a single card. This driver model is centered +on the notion of reading bitfields from the card. + +There are currently no discrete I/O 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 +discrete I/O 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 +that specify a particular bitfield. This results in categories +like the following: + +- *board* - indicates the board a particular bitfield is located on + +- *word* - indicates the particular word of discrete bits the + bitfield is located within + +- *start* - indicates the starting bit of the bitfield + +- *width* - indicates the width of the bitfield + +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. + +By providing a way to easily access a particular bitfield from +the device driver, the application is insulated with knowing how +to mask fields in and out of a discrete I/O. + +Discrete I/O Driver Configuration +================================= + +There is not a standard discrete I/O driver configuration table but some +fields are common across different drivers. The discrete I/O 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 discrete I/O board: + +*board_offset* + is the base address of a board. + +*relay_initial_values* + is an array of the values that should be written to each output + word on the board during initialization. This allows the driver + to start with the board’s output in a known state. + +Initialize a Discrete I/O Board +=============================== + +At system initialization, the discrete I/O driver’s initialization entry point +will be invoked. As part of initialization, the driver will perform +whatever board initializatin is required and then set all +outputs to their configured initial state. + +The discrete I/O driver may register a device name for bitfields of +particular interest to the system. Normally this will be restricted +to the names of each word and, if the driver supports it, an "all words". + +Open a Particular Discrete Bitfield +=================================== + +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 Discrete Bitfield +==================================== + +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 Discrete Bitfield +======================================== + +This corresponds to the driver read call. After validating the minor +number and arguments, this call reads the indicated bitfield. A +discrete I/O devices may have to store the last value written to +a discrete output. If the bitfield is output only, saving the last +written value gives the appearance that it can be read from also. +If the bitfield is input, then it is sampled. + +*NOTE:* Many discrete inputs have a tendency to bounce. The application +may have to take account for bounces. + +The value returned is an ``unsigned32`` number +representing the bitfield read. This value is stored in the``argument_block`` passed in to the call. + +*NOTE:* Some discrete I/O drivers have a special minor number +used to access all discrete I/O bits on the board. If this special +minor is used, then the area pointed to by ``argument_block`` must +be the correct size. + +Write to a Particular Discrete Bitfield +======================================= + +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 an ``unsigned32`` number +representing the value to be written to the specified +bitfield. This value is stored in the``argument_block`` passed in to the call. + +*NOTE:* Some discrete I/O drivers have a special minor number +used to access all discrete I/O bits on the board. If this special +minor is used, then the area pointed to by ``argument_block`` must +be the correct size. + +Disable Discrete Outputs +======================== + +This is one of the IOCTL functions supported by the I/O control +device driver entry point. When this IOCTL function is invoked, +the discrete outputs are disabled. + +*NOTE:* It may not be possible to disable/enable discrete output on all +discrete I/O boards. + +Enable Discrete Outputs +======================= + +This is one of the IOCTL functions supported by the I/O control +device driver entry point. When this IOCTL function is invoked, +the discrete outputs are enabled. + +*NOTE:* It may not be possible to disable/enable discrete output on all +discrete I/O boards. + +Reinitialize Outputs +==================== + +This is one of the IOCTL functions supported by the I/O control +device driver entry point. When this IOCTL function is invoked, +the discrete outputs are rewritten with the configured initial +output values. + +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 output word + +- timestamp of when the last write was performed + -- cgit v1.2.3