Figure 5.4: Waveform with Multiple Cycles
EFFICIENCY
A certain amount of overhead is involved in the handling of audio DMA. If you are trying
to produce a smooth continuous audio synthesis, you should try to avoid as much of the
system control overhead as possible. Basically, the larger the audio buffer you provide to
the system, the less often it will need to interrupt to reset the pointers to the top of the
next buffer and, coincidentally, the lower the amount of system interaction that will be
required. If there is only one waveform buffer, the hardware automatically resets the
pointers, so no software overhead is used for resetting them.
The "Joining Tones" section illustrated how you could join "ends" of tones together by
responding to interrupts and changing the values of the location registers to splice tones
together. If your system is heavily loaded, it is possible that the response to the interrupt
might not happen in time to assure a smooth audio transition. Therefore, it is advisable to
utilize the longest possible audio Table where a smooth output is required. This takes
advantage of the audio DMA capability as well as minimizing the number of interrupts to
which the 68000 must respond.
- Audio Hardware 149 -
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