An Amiga device is a software module that accepts commands and data and performs I/O operations based on the commands it receives. In most cases, it interacts with either internal or external hardware, (the exceptions are the clipboard device and ramdrive device which simply use memory). Generally, an Amiga device runs as a separate task which is capable of processing your commands while your application attends to other things. Table 19-1: Amiga System Devices Amiga Device Purpose ------------ ------- Audio Controls the use of the audio hardware. Clipboard Manages the cutting and pasting of common data blocks Console Provides the line-oriented user interface. Gameport Controls the two mouse/joystick ports. Input Processes input from the gameport and keyboard devices. Keyboard Controls the keyboard. Narrator Produces the Amiga synthesized speech. Parallel Controls the parallel port. Printer Converts a standard set of printer control codes to printer specific codes. SCSI Controls the Small Computer Standard Interface hardware. Serial Controls the serial port. Timer Provides timing functions to measure time intervals and send interrupts. Trackdisk Controls the Amiga floppy disk drives. The philosophy behind the devices is that I/O operations should be consistent and uniform. You print a file in the same manner as you play an audio sample, i.e., you send the device in question a WRITE command and the address of the buffer holding the data you wish to write. The result is that the interface presented to the programmer is essentially device independent and accessible from any computer language. This greatly expands the power the Amiga brings to the programmer and, ultimately, to the user. Devices support two types of commands: Exec standard commands like READ and WRITE, and device specific commands like the trackdisk device MOTOR command which controls the floppy drive motor, and the keyboard device READMATRIX command which returns the state of each key on the keyboard. You should keep in mind, however, that supporting standard commands does not mean that all devices execute them in exactly the same manner. This chapter contains an introduction to the Exec and amiga.lib functions that are used when accessing Amiga devices. Consult the Amiga ROM Kernel Manual: Devices volume for chapters on each of the Amiga devices and the commands they support. In addition, the Amiga ROM Kernel Reference Manual: Includes and Autodocs contains Autodocs summarizing the commands of each device, and listings of the device include files. Both are very useful manuals to have around when you are programming the devices.
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