Force Computers SYS68K/CPU-40, User Manual

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SYS68K/CPU-39 USER'S MANUAL FORCE COMPUTERS
I-2
I.1.1 Acquire the RAM port
The OPEN command requests the establishment of a logical connection between an application and
the RAM port; the appropriate Command Control Buffer is structured as presented in
Figure 1.
Whenever an OPEN command is issued through the Application Command Interface to 'open' the RAM
port, the Management Entity verifies whether the RAM port is still available and in this case it takes
possession of the RAM port. If the RAM port is already owned by another application, the attempt to
acquire the RAM port is refused by the Management Entity.
struct _ccb_open_command
{
unsigned long _access_control_flags;
unsigned long _reserved_for_ME_purpose[ 10 ];
unsigned long command;
unsigned long logical_device_code;
unsigned long inquiry_mode;
unsigned long response_mode;
unsigned long data_exchange_mode;
unsigned long application_address;
unsigned long _remnant[ 47 ];
};
Figure 1: Structure of the CCB used to gain RAM port ownership
The OPEN Command is to execute as described in the Application Command Interface Programming
Guide.
logical_device_code:
Because the RAM port is permanently available through the ACI, the major and minor device number
of the RAM port are always the same: both the major device number of $0 and the minor device
number -4 ($FC) specify the RAM port. (The Management Entity keeps track of the major device
numbers of all devices available on present EAGLE modules; and due to the fact that the RAM port
is managed by the ME directly and because it is permanently available through the ACI independent
of the presence of any EAGLE module, the ME orders the RAM port at the beginning of its internal
device list. Therefore, the major device number assigned to the RAM port by the ME is $0 and the
minor device number -4 denotes the proper RAM port.)