code: func SpiSpeed(speed int) {
  	const baseFreq = 250 * 1000000
  	cdiv := uint32(baseFreq / speed)
  	setSpiDiv(cdiv)
  }
docs: // SpiSpeed: Set (maximal) speed [Hz] of SPI clock.
  // Param speed may be as big as 125MHz in theory, but
  // only values up to 31.25MHz are considered relayable.