Direct Memory Access
Under the Amiga architecture, the Agnus (Alice on AGA models) coprocessor is the direct memory access (DMA) controller. Both the CPU and other members of the chipset have to arbitrate for access to shared RAM via Agnus. This allows the custom chips to perform video, audio or other DMA operations independently of the CPU. As the 68000 processor used in early Amiga systems usually accesses memory on every second memory cycle, Agnus operates a system where the "odd" clock cycle is allocated to time-critical custom chip access and the "even" cycle is allocated to the CPU, thus the CPU is not typically blocked from memory access and may run without interruption. However, certain chipset DMA, such as copper or blitter operations, can use any spare cycles, effectively blocking cycles from the CPU. In such situations CPU cycles are only blocked while accessing shared RAM, but never when accessing external RAM or ROM.
Read more about this topic: Amiga Chip RAM
Famous quotes containing the words direct, memory and/or access:
“The shortest route is not the most direct one, but rather the one where the most favorable winds swell our sails:Mthat is the lesson that seafarers teach. Not to abide by this lesson is to be obstinate: here, firmness of character is tainted with stupidity.”
—Friedrich Nietzsche (1844–1900)
“Near this spot are deposited the remains of one who possessed Beauty without Vanity, Strength without Insolence, Courage without Ferocity, and all the Virtues of Man without his Vices. This praise, which would be unmeaning Flattery, if inscribed over human ashes, is but a just Tribute to the Memory of BOATSWAIN, a Dog.”
—John Cam Hobhouse (1786–1869)
“A girl must allow others to share the responsibility for care, thus enabling others to care for her. She must learn how to care in ways appropriate to her age, her desires, and her needs; she then acts with authenticity. She must be allowed the freedom not to care; she then has access to a wide range of feelings and is able to care more fully.”
—Jeanne Elium (20th century)