About This Ohapter; What Is A Copper Instruction - Commodore Amiga Hardware Reference Manual

One of the features of the Copper is its ability to WAIT for a specific video beam posi-
tion, then MOVE data into a system register. During the WAIT period, the Copper
examines the contents of the video beam position counter directly. This means that
while the Copper is waiting for the beam to reach a specific position, it does not use the
memory bus at all. Therefore, the bus is
free~
for use by the other DMA channels or by
the 68000.
When the WAIT condition has been satisfied, the Copper steals memory cycles from
either the blitter or the 68000 to move the specified data into the selected special-
purpose register.
The Copper is a two-cycle processor that requests the bus only during odd-numbered
memory cycles. This prevents collision with audio, disk, refresh, sprites, and most low-
resolution display DMA access, all of which use only the even-numbered memory cycles.
The Copper, therefore, needs priority over only the 68000 and the blitter (the DMA
channel that handles animation, line drawing, and polygon filling).
As with all the other DMA channels in the Amiga system, the Copper can retrieve its
instructions only from the lowest 512K bytes of system memory.
ABOUT THIS CHAPTER
In this chapter, you will learn how to use the special Copper instruction set to organize
mid-screen register value modifications and pointer register set-up during the vertical
blanking interval. The chapter shows how to organize Copper instructions into Copper
lists, how to use Copper lists in interlaced mode, and how to use the Copper with the
blitter. The Copper is discussed in this chapter in a general fashion. The chapters that
deal with playfields, sprites, audio, and the blitter contain more specific suggestions for
using the Copper.
What is a Copper Instruction?
As a coprocessor, the Copper adds its own instruction set to the instructions already
provided by the 68000. The Copper has only three instructions, but you. can do a lot
with them:
8 Coprocessor Hardware