Force Computers SYS68K/CPU-40, User Manual

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SYS68K/CPU-40/41 USER'S MANUAL FORCE COMPUTERS
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As mentioned above the application accesses devices on an EAGLE module via a logical connection,
rather than directly. Therefore, each device accessible through the Application Command Interface is
identified by a unique logical device number which is provided by the interface.
A base board providing the Application Command Interface deposits the NUL terminated string "ACI"
beginning at offset $0 of the board's main memory accessible from the VMEbus; and the VMEbus address
of the first Command Control Buffer (CCB 0), provided by the Application Command Interface, is loaded
into the long word at offset $4. Thus, the application intending to communicate with devices through the
Application Command Interface, or to get generic information about available devices, has to look for the
"ACI" identifier within the VMEbus' standard (A24) and extended (A32) address range.
Any application has to verify whether the base board the application is running on provides the Application
Command Interface, too.
If the application has found a board providing the interface, it has to use the first Command Control Buffer,
addressed by the content of the long word at offset $4 of the board's memory, either to issue the SERVICE
command to get information about the available devices or other information about the EAGLE modules;
or to issue the OPEN command to establish a logical connection between the application and a specific
device.
However, before the application uses the first Command Control Buffer to issue a command through the
Application Command Interface it has to gain the ownership of the first Command Control Buffer.
The detailed structure of a Command Control Buffer is described in the subsection "The Command Control
Buffers".
The Command Control Buffer contains some semaphores to be used to control the access to the buffer,
and to indicate various states of the Command Control Buffer. To gain the ownership of the Command
Control Buffer a semaphore has to be set to indicate that the buffer is already in use by an application. Due
to this fact, the application has to verify the state of this semaphore, and if the semaphore is cleared, that
means the Command Control Buffer is available, the application has to set it to prevent the Command
Control Buffer from being acquired by another application.
When the application has the ownership of the first Command Control Buffer, it has to prepare the buffer
to issue the particular command. The application can only issue the OPEN command or the SERVICE
command, to get generic information, through the Application Command Interface. All other commands
(CLOSE, READ, and WRITE) are refused by the Application Command Interface because no logical
connection between the application and a device exists.