mcp3kadc —
Microchip 3x0x SAR analog to digital converter
mcp3kadc* at spi? slave ? flags N
The mcp3kadc driver reports the current voltage on the
  chip's ADC channels through the
  envsys(4) API. The driver
  calculates these values according to the currently selected reference voltage
  (Vref). It can be changed through the
  sysctl(8) node
  hw.mcp3kadc0.vref.
The following table shows the supported chips. The type of the
    chip can be selected with the flags argument in the
    config file.
The following sysctl(3) variables
  are provided:
  - hw.mcp3kadc0.vref
- Defines the reference voltage on the chip's Vrefpin in millivolts (mV). It defaults to the ADC's maximum output value + 1
      in millivolts (e.g., 4096 for a 12-bit ADC).
Themcp3kadc driver first appeared in
  NetBSD 8.0.
The mcp3kadc driver was written by
  Frank Wille.