The Amiga co-processor
While AMOS Professional allows you to harness the power of the Amiga with the greatest of
ease, it has to perform a great deal of work behind the scenes when manipulating entire screens
at great speed. The source of much of this power is a special hardware chip called the "co-
processor", or copper.
The copper is in effect a simple micro-processor, with its own separate programs, and its own unique memory registers. It supports only three instructions, MOVE, WAIT and SKIP, and these commands insert values into the computer's hardware registers at certain points on the display, which change the way pictures are drawn on the screen.
These hardware registers hold the values that determine the precise appearance of the display, such as its size and position, as well as the number of colours. For example, all the colour values used by AMOS Professional screens are held in the colour registers from $180 to $1BE. Because the appearance of every line displayed on your screen is controlled by the copper, a massive number of special effects can be created by changing these registers during a program, using a list of instructions known as the "copper list".
The Copper List
The copper list is executed automatically, fifty times every second, at the same time that the
screen is re-drawn. This is how the AMOS Professional RAINBOW commands work, waiting for
a rainbow line to appear on screen and then immediately poking a new value into the selected
colour register. This causes dramatic colour changes, depending on the position of the line in the
display.
Exactly the same process can be applied to the rest of the display system, and by placing the appropriate value into certain hardware registers at exactly the right moment, the position, type and size of the display can be changed at will! Unfortunately, the copper list is notoriously difficult to manipulate, and many competent programmers have failed to master its mysteries.
Although the copper is automatically managed by AMOS Professional, you cannot expect the system to teach you everything about the inner workings of the Amiga's hardware. Indeed, Francois Lionet has written AMOS Professional to save you the years of hard work and experience needed to gain such expert knowledge. However, for those expert programmers who insist on meddling with the copper directly, AMOS Professional includes a powerful trap- door into the realms of the co-processor. This allows advanced programmers to generate astounding effects, and also allows novices to send their displays berserk and crash their computers. You have been warned!
Accessing the Copper
COPPER OFF
instruction: turn off the standard copper list
Copper Off
If you ignore the warning in the last paragraph and use this instruction, the automatic copper generation that forms the backbone of the AMOS Professional system is turned off. From now on, you are on your own!