Many different direct memory access (DMA) functions occur during system operation. There is a read address as well as a write address to the DMA control register so you can tell which DMA channels are enabled. The address names for the DMA registers are as follows: DMACONR - Direct Memory Access Control - read-only. DMACON - Direct Memory Access Control - write-only. The contents of this register are shown in Table 7-6 (bit on if enabled). Bit Number Name Function ------ ---- -------- 15 SET/CLR The set/reset control bit. See description of bit 15 . 14 BBUSY Blitter busy status - read-only 13 BZERO Blitter zero status - read-only. Remains 1 if, during a blitter operation, the blitter output was always zero. 12, 11 Unassigned 10 BLTPRI Blitter priority. Also known as "blitter-nasty." When this is a 1, the blitter has full (instead of partial) priority over the 680x0. 9 DMAEN DMA enable. This is a master DMA enable bit. It enables the DMA for all of the channels at bits 8-0. 8 BPLEN Bitplane DMA enable 7 COPEN Coprocessor DMA enable 6 BLTEN Blitter DMA enable 5 SPREN Sprite DMA enable 4 DSKEN Disk DMA enable 3-0 AUDxEN Audio DMA enable for channels 3-0 (x = 3 - 0). Table 7-6: Contents of DMA Control Register For more information on using the DMA, see the following chapters: Copper Chapter 2: Coprocessor Hardware Bitplanes Chapter 3: Playfield Hardware Sprites Chapter 4: Sprite Hardware Audio Chapter 5: Audio Hardware Blitter Chapter 6: Blitter Hardware Disk Chapter 8: Interface Hardware Processor Access To Chip Memory ------------------------------- The Amiga chips access Chip memory directly via DMA, rather than utilizing traditional bus arbitration mechanisms. Therefore, processor supplied features for multiprocessor support, such as the 68000 TAS (test and set) instruction, cannot serve their intended purpose and are not supported by the Amiga architecture.
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