Force Computers SYS68K/CPU-40, User Manual

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SECTION 9 APPLICATION COMMAND INTERFACE PROGRAMMING GUIDE
1-5
1.2 The Command Control Buffers
As mentioned previously the Command Control Buffer is the basic data structure to issue commands
through the Application Command Interface. This data structure of 256 bytes size consists of two logical
parts.
The first part (44 bytes) is used to store global information for the device driver dealing with the device the
Command Control Buffer is associated with, to control the access to the Command Control Buffer and to
reflect the state of a Command Control Buffer.
The second part (212 bytes) is exclusively used to specify the command to be issued through the
Application Command Interface, as well as the parameters that accompanies the command. All status
information reflecting the course of the processed command are passed through this area to the
application.
The generic structure of a Command Control Buffer is described below (using the C programming language
elements):
typedef struct _ccb
{
unsigned long _access_control_flags;
long ( *ME_system_call ) ( );
struct _ccb *ccb_link;
long last_command;
unsigned long _reserved[ 7 ];
long command_or_status;
unsigned long remnant[ 52 ];
} CCB;
The first eleven entries in the data structure described above are common to all Command Control Buffers,
independent from the command being issued through the Application Command Interface. The structure
of the remaining 53 entries depend on the command issued, and whether the Command Control Buffer is
"passed" to the Application Command Interface or "returned" to the application through the Application
Command Interface.
unsigned long _access_control_flags
This entry represents the Access Control Field consisting of semaphores to control the access
to the Command Control Buffer and to reflect the state of the Command Control Buffer.