Force Computers SYS68K/CPU-40, Руководство пользователя

Страница: 349 / 372

SECTION 9 APPLICATION COMMAND INTERFACE PROGRAMMING GUIDE
2-21
2.5 The SERVICE Command
The SERVICE command requests special services provided by the Application Command Interface and
a specific device driver. The Application Command Interface provides services to control the device
driver's parameter, such as task priority etc., or to allocate additional memory which is dedicated to a
logical connection; and a device driver provides services to modify the hardware parameter of a
peripheral (changing the transmission rate of a serial communication controller, to enable or disable
special functions implemented in the peripheral, like timers, counters, etc.) or to change the operating
mode of the device driver. The structure of the Command Control Buffer to issue a SERVICE
command is described below.
typedef struct _ccb_service_command
{
unsigned long _access_control_flags;
long ( *ME_system_call ) ( );
CCB *ccb_link;
long last_command;
unsigned long _reserved[ 7 ];
long command;
long service;
unsigned long service_parameter[ 51 ];
} CCB_SERVICE_COMMAND;
_access_control_flags:
The BUSY semaphore has to be set to indicate the readiness of the Command Control Buffer
to be processed; all other semaphores within the Access Control Field have to be left unaffected.
command:
The value $10 indicates that the command control buffer is used to issue the SERVICE command
through the Application Command Interface.