Alsa state chooser

[TL Mieszkowski]

WM8753.pdf pg 27:
MICBIAS CURRENT DETECT
The WM8753L includes a microphone bias current detect circuit which allows
the user to set
thresholds for the microphone bias current, above which an interrupt will be
triggered. There are two
separate interrupt bits, MICDET to allow the user to e.g. distinguish
between one or two microphones
connected to the WM8753L, and MICSHT to detect a shorted microphone (mic
button press). The
thresholds for the microphone bias current are set by MBTHRESH[2:0], for
MICDET, and
MBSCTHRESH[1:0] for MICSHT. Thresholds for each code are shown in Table 15.
The circuit is
enabled by setting MBCEN.
See the GPIO and Interrupt Controller sections for details on the interrupt
and status readback for the
microphone bias current detect.
  REGISTER        BIT        LABEL          DEFAULT                  
DESCRIPTION
  ADDRESS
 R51 (33h)       5:4     MBSCTHRESH         00           Microphone Bias,
Shorted Current
                                                         Threshold Select
                                                         00: 500uA
                                                         01: 1000uA
                                                         10: 1600uA
                                                         11: 2300uA
                                                         These values are
for 3.3V supply and
                                                         scale with supply
voltage.
                 3:1     MBTHRESH           000          Microphone Bias,
Current Threshold
                                                         Select
                                                         000:250uA
                                                         001:410uA
                                                         ....160uA steps up
to
                                                         111:1370uA
                                                         These values are
for 3.3V supply and
                                                         scale with supply
voltage.
                 0       MBCEN              0            Mic Bias Current
Comparator Circuit
                                                         enable
                                                         0 : Comparator
disabled
                                                         1 : Comparator
enabled
Table 15 Mic Bias Current Comparator Circuit Control

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