DECIDING WHICH CHANNEL TO USE........................134 CREATING THE WAVEFORM DATA...........................134 TELLING THE SYSTEM ABOUT THE DATA ...................136 SELECTING THE VOLUME ................................136 SELECTING THE DATA OUTPUT RATE.......................137 PLAYING THE WAVEFORM ................................140 STOPPING THE AUDIO DMA...............................141 SUMMARY..............................................142 EXAMPLE..............................................142 Producing Complex Sounds................................143 JOINING TONES .......................................143 PLAYING MULTIPLE TONES AT THE SAME TIME..............145 MODULATING SOUND ....................................145 Producing High-quality Sound............................148 MAKING WAVEFORM TRANSITIONS .........................148 SAMPLING RATE .......................................148 EFFICIENCY...........................................149 NOISE REDUCTION......................................150 ALIASING DISTORTION .................................150 LOW-PASS FILTER .....................................152 Using Direct (Non-DMA) Audio Output ....................153 The Equal-tempered Musical Scale........................154 Decibel Values for Volume Ranges .......................159 The Audio State Machine.................................160 Chapter 6 BLITTER HARDWARE................................163 Introduction............................................163 Memory Layout ..........................................164 DMA Channels............................................164 Function Generator......................................168 DESIGNING THE LF CONTROL BYTE WITH MINTERMS..........169 DESIGNING THE LF CONTROL BYTE WITH VENN DIAGRAMS.....172 Shifts and Masks........................................173 Descending Mode ........................................176 Copying Arbitrary Regions...............................177 Area Fill Mode..........................................178 Blitter Done Flag.......................................180 MULTITASKING AND THE BLITTER ........................181 Interrupt Flag .........................................181 Zero Flag...............................................182 Pipeline Register.......................................182 Line Mode...............................................184 REGISTER SUMMARY FOR LINE MODE.......................186 Blitter Speed ..........................................188 Blitter Operations and System DMA ......................189 Blitter Block Diagram...................................193 Blitter Key Points......................................195 EXAMPLE:
ClearMem....................................195 EXAMPLE: SimpleLine..................................197 EXAMPLE: RotateBits..................................199 Chapter 7 SYSTEM CONTROL HARDWARE ........................201 Introduction............................................201 Video Priorities .......................................202 FIXED SPRITE PRIORITES ..............................202 HOW SPRITES ARE GROUPED..............................203 UNDERSTANDING VIDEO PRIORITIES ......................203 SETTING THE PRIORITY CONTROL REGISTER................204 Collision Detection ....................................207