'-------------------------------------------------------------------------------
Option Explicit

' This is an easier-to-use version of OpenSPI.
'-------------------------------------------------------------------------------
Public Sub Main()

    Dim Channel As Byte
    Dim ChipSelectPin As Byte
    Dim LSBFirst As Boolean
    Dim ClockPolarity As Boolean
    Dim ClockPhase As Boolean
    Dim MaxClockRate As Long
    Dim PinNumber As Byte

    ' Example of SPI on channel 1 with clock rate no greater than 2.1 MHz.
    Channel = 1
    ChipSelectPin = 17
    LSBFirst = False
    ClockPolarity = False
    ClockPhase = False
    MaxClockRate = 2100000  ' Hz

    Call SPIOpenChannel(Channel, ChipSelectPin, LSBFirst, ClockPolarity, _
        ClockPhase, MaxClockRate)

    ' [...]

End Sub
'-------------------------------------------------------------------------------
Private Sub SPIOpenChannel( _
    ByVal Channel As Byte, _
    ByVal ChipSelectPin As Byte, _
    ByVal LSBFirst As Boolean, _
    ByVal ClockPolarity As Boolean, _
    ByVal ClockPhase As Boolean, _
    ByVal MaxClockRate As Long)

    Const SPIRateDiv4   As Byte = bx0000_0000   ' Clock speed = f/4
    Const SPIRateDiv16  As Byte = bx0000_0001   ' Clock speed = f/16
    Const SPIRateDiv64  As Byte = bx0000_0010   ' Clock speed = f/64
    Const SPIRateDiv128 As Byte = bx0000_0011   ' Clock speed = f/128

    Dim ClockRateSelect As Byte

    ' See Atmel documentation for these bits.
    Const DORD As Byte = bx0010_0000   ' Data order, LSB first.
    Const CPOL As Byte = bx0000_1000   ' Clock polarity, SCK high when idle.
    Const CPHA As Byte = bx0000_0100   ' Clock phase.

    Dim SetupByte As Byte

    ' Safety clamp.
    If (Channel < 1) Then
        Channel = 1
    ElseIf (Channel > 4) Then
        Channel = 4
    End If

    ' Pick a clock rate as close as possible to MaxClockRate but without
    ' exceeding the rate.
    If (MaxClockRate >= 1843200) Then

        ClockRateSelect = SPIRateDiv4     ' Fastest.

    ElseIf (MaxClockRate >= 460800) Then

        ClockRateSelect = SPIRateDiv16

    ElseIf (MaxClockRate >= 115200) Then

        ClockRateSelect = SPIRateDiv64

    ElseIf (MaxClockRate >= 57600) Then

        ClockRateSelect = SPIRateDiv128   ' Slowest.
    Else
        ' Error, choose slowest speed.
        ClockRateSelect = SPIRateDiv128
    End If

    SetupByte = ClockRateSelect

    If (LSBFirst) Then
        SetupByte = SetupByte Or DORD
    End If

    If (ClockPolarity) Then
        SetupByte = SetupByte Or CPOL
    End If

    If (ClockPhase) Then
        SetupByte = SetupByte Or CPHA
    End If

    Call OpenSPI(Channel, SetupByte, ChipSelectPin)

End Sub
'-------------------------------------------------------------------------------