MIC_StartLimitedSampling

Syntax

#include <twl/spi.h>
MICResult MIC_StartLimitedSampling(
            const MICAutoParam*    param );

Arguments

param Specifies a pointer to a MICAutoParam-type auto-sampling settings structure.

Return Values

Returns the processing result as a MICResult enumerated type. Returns MIC_RESULT_SUCCESS if processing completed successfully; returns some other value if the process failed.

Description

Starts frequency-limited microphone auto-sampling.
This function issues a request to the ARM7 to start frequency-limited auto-sampling, waits for the ARM7 to respond, and returns the processing result. This is a synchronous version of the MIC_StartLimitedSamplingAsync function. Where the input volume falls outside the minimum or maximum value, the sampling data will be clamped.

Frequency-limited auto-sampling differs from normal auto-sampling in that the hardware does the actual sampling. As a result, stable sampling can be performed at precise cycles; also, by relaxing the CPU burden on the ARM7, effects of sampling on wireless communications and other I/O will be reduced. On the other hand, sampling cannot be performed at frequencies that are unsupported by the hardware. The following sampling frequencies can be specified for param ->rate, but the frequencies that can be specified at a given time depend on the sound master frequency settings and thus are further limited to four of the following. A value of MIC_RESULT_ILLEGAL_PARAMETER will be returned if one of the limited frequencies is not specified.

Sound master frequency
Settable frequency
Description
32.73kHz MIC_SAMPLING_RATE_32730 32.73kHz (1/1 of the master frequency)
MIC_SAMPLING_RATE_16360 16.36kHz (1/2 of the master frequency)
MIC_SAMPLING_RATE_10910 10.91kHz (1/3 of the master frequency)
MIC_SAMPLING_RATE_8180 8.18kHz (1/4 of the master frequency)
47.61kHz MIC_SAMPLING_RATE_47610 47.61kHz (1/1 of the master frequency)
MIC_SAMPLING_RATE_23810 23.81kHz (1/2 of the master frequency)
MIC_SAMPLING_RATE_15870 15.87kHz (1/3 of the master frequency)
MIC_SAMPLING_RATE_11900 11.90kHz (1/4 of the master frequency)

Note

This function waits for a PXI interrupt for synchronization purposes. Do not call it when PXI interrupts are prohibited.

Because frequency-limited auto-sampling cannot be performed on the NITRO platform or when the CODEC is running in CODEC-DS mode, this function will instead internally call the MIC_StartAutoSampling auto-sampling control function.

It has been confirmed that slight hardware noise is mixed with the microphone input on the TWL console. See here for a workaround.

See Also

MIC_StartLimitedSamplingAsync, MIC_StopLimitedSampling, MIC_AdjustLimitedSampling

Revision History

2008/01/09 Added a note about the difference in behavior with CODEC mode.
2007/11/17 Initial version.


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