'
' LEGO Rotation Sensor test code
'
' Encoder on PA0 and switch/light sensor on PA7
'
' The lego rotation sensor is queried roughly 122hz
'
$regfile = "m16def.dat"
$crystal = 8000000
$baud = 19200
'

Config Timer0 = Timer , Prescale = 256
On Timer0 Timer0_isr                                        ' Our timer interrupt hanlder
Enable Timer0
Enable Interrupts
'
Config Pinb.4 = Output
Prog_led Alias Portb.4                                      ' LED for winkie
'
Declare Sub Init_encoder()
Declare Function Encoder() As Integer
Declare Sub Doencoder()
Declare Function Light() As Byte
Declare Function Switch() As Byte

Call Init_encoder()
'
Dim My_encoder As Integer
Dim Sys_timer As Byte , Temp As Integer
'
' Do loop prints out only when Encoder changes value
'
Do
    Temp = Encoder()
    If My_encoder <> Temp Then
        My_encoder = Temp
        Print "Encoder=" ; My_encoder ; " Light=" ; Light()
    End If
    Idle                                                    ' Sleep until next interrupt.
Loop
End
'
Timer0_isr:
'
' State machine to flash LED at 1 hz.  Note: the main loop code can use
' the value of Sys_timer to measure out time in 8 ms increments.
'
    Incr Sys_timer
    If Sys_timer = 25 Then
        Prog_led = 0                                        'enable low output (ON)
    Elseif Sys_timer = 125 Then
        Prog_led = 1                                        'disable output (OFF)
        Sys_timer = 0                                       'reset timer
    End If
    '
    Call Doencoder()
    '
    Return
'
Dim Enc_prev As Byte , Enc_val As Integer , Enc_tmp As Byte , Light_tmp As Integer

Function Encoder() As Integer
   Encoder = Enc_val
   End Function

Sub Init_encoder()
   ' Note: atmel doesn't recommend running the ADC this fast
   ' but as far as I can tell it works fine.  The results will be noiser
   ' but only by 2-4 counts.
   Config Adc = Single , Prescaler = 8
   Start Adc
End Sub
'
' Read and decode the LEGO rotation sensor.  (port A0)
'
' The speed at which the encoder can be read is determined
' by the call rate.  This sample calls at 122hz
' which should give a top speed of ~300rpm
'
Sub Doencoder()
   Ddra.0 = 0
   Porta.0 = 0
   Waitus 5
   Select Case Getadc(0)
   Case Is > 850 :
         Enc_tmp = 2
         If Enc_prev = 1 Then Goto Inc_encoder
         If Enc_prev = 3 Then Goto Dec_encoder
   Case Is > 700 :
         Enc_tmp = 1
         If Enc_prev = 0 Then Goto Inc_encoder
         If Enc_prev = 2 Then Goto Dec_encoder
   Case Is > 450 :
         Enc_tmp = 3
         If Enc_prev = 2 Then Goto Inc_encoder
         If Enc_prev = 0 Then Goto Dec_encoder
   Case Else :
         Enc_tmp = 0
         If Enc_prev = 3 Then Goto Inc_encoder
         If Enc_prev = 1 Then Goto Dec_encoder
   End Select
   Goto No_encoder
Inc_encoder:
   Enc_val = Enc_val + 2
Dec_encoder:
   Enc_val = Enc_val - 1
No_encoder:
   Porta.0 = 1
   Ddra.0 = 1
   Enc_prev = Enc_tmp
End Sub

'
' Read a LEGO light sensor. (port A7)
'
' The raw output varies from ~600 to ~900, 
' depending.  I clip the output and shift 
' it & invert so low numbers == dark and 
' high numbers equal light.  If you 
' parallel a switch on this port a switch 
' closure will read as 0.  If only a switch 
' is on this port, it will read 255 (open)
' and 0 (closed)
'
Function Light() As Byte
   Ddra.7 = 0
   Porta.7 = 0
   Waitus 10
   Light_tmp = Getadc(7)
   If Light_tmp < 600 Then
      Light = 0
   Elseif Light_tmp > 855 Then
      Light = 255
   Else
      Light = 875 - Light_tmp
   End If
   Porta.7 = 1
   Ddra.7 = 1
End Function

'
' Read LEGO switch (port A7)
'
' functionally redundant with Light(), but
' consumes less power as the outputs are not driven.
' NB - calling this will mess up logic for Light().  Use
' one or the other but not both.
'
Function Switch() As Byte
   Ddra.7 = 0
   Waitus 5
   Switch = Pina.7
End Function

'end program