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DACS: Component Functional Design
 
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Component Functional Design

Mixer jobs may be requested by the host computer. These jobs complete in a finite amount of time. They can range from simply setting a particular mixer register to a value instantaneously to slowly fading sets of registers up or down over time. Several ``slots'' for jobs shall be available, allowing multiple concurrent jobs that start and end at different times. Figure 100 diagrammatically shows the mixer job engine. Note that the earliest free slot is always used for an incoming job (the position of job 4 shows this well). The time scale used is of arbitrary granularity, and should be chosen for convenience. A value of between 1/10th and 1/100th of a second should suffice for this application. The specific granularity should be chosen with an eye towards human perceptibility and microcontroller loading.

Figure 100: Mixer jobs, job slot vs. time.
\begin{figure}
\psfig{file=fw/mixer-jobs.eps,width=6in}
\end{figure}

Several different types of jobs may be requested from the host, as shown in table 10. Some of the jobs allow for a variable time-to-completion. This allows variable-length audio fades to occur. Some jobs, mainly task management jobs, complete in a single time tick.

Table 10: Mixer job table.
Job Time Units Description
mixer reset 1 Reset mixer unit to default state; Cancel all jobs.
stop running job 1 Stop a particular running job, return value to initial state.
fade without notify n Over n time units, fade mixer register from
    initial value to ending value, interpolating as necessary.
fade with notify n Over n time units, fade mixer
    register from initial value to ending value,
    interpolating as necessary. Notify host upon completion.


The mixer unit also has provisions for an add-on digital VU meter. This dictates that a means for the retrieval of the VU data be available. In addition, information about the installed modules in the mixer unit may be requested by the host computer.
next up previous contents
Next: The DACS Firmware Library Up: Mixer Unit Previous: Overall Functional Design   Contents
Steve Richardson 2000-07-06
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