Grage Aeromodelling

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' #################################################
' ####                                          ###
' ####               PPM-Encoder                ###
' ####               Version 1.0                ###
' ####     PPM-Decoder and SMART-PPM-Decoder    ###
' ####                                          ###
' #################################################


' Software PPM-Decoder and SMART-PPM-Decoder Version 1.0

' Decodes a 1 to 8-channel RC-sum signal (PPM) for direct servo-control.
' To the servo-output is the pulse signal (1ms to 2ms).


' CPU:                  ATtiny44V (DIP/SOIP)
' Clock:                RC-Internal Oscillator 8MHz / 8 (System-Clock = 1MHz)
' Compiler:             1.11.9.2
' Source:               Version 1.0
' Author:               M. Ruhwald 2008 (www.MitchSoft.de)
' Created:              11.07.2008
' Last change:          03.08.2008

' Resources:
' INT0 - RC-PPM signal (Input)
' OC1A - Interrupt (PPM-Timeout)
' OC1B - Interrupt (Frame-Start)
' Timer1 - Counter (1MHz)

' Pinning:
' PortA   - Servo Outputs channel 1 to 8
' PortB.0 - LED (red for error); non-SMART version
' PortB.1 - LED (yellow blink for receiving), non-Smart Version
' PortB.2 - Input PPM-Signal
' PortB.3 - Reset

' ---------------------------------------------------------------------------------------

' FUNCTIONAL DESCRIPTION

' Principle:
' Timer1 is configured as a counter. It is clocked with a clock of 1.0 MHz.
' This per clock a time of 1.0 microseconds elapses.
' The Timer1 causes two interrupts, namely OC1A and OC1B.

' OC1A is used to
' to identify a missing PPM signal. The value is set to RC_Timeout,
' and corresponds to a time of 50 milli-seconds. If during this time, no edges
' detected on the INT0 input, the interrupt is triggered and calls the routine _ISR_INT0.
' The timer is automatically reset to zero.

' OC1B is used to detect the start signal of a pulse train. The value for
' Compare1B is set to RC_Frame and corresponds to a time of 2.5 milli-seconds.
' If at this time no edge occurs, the interrupt occurs and the routine
' _ISR_OC1B called.

' The RC-sum signal (PPM) ICP1 the input is supplied. For each negative edge
' a ICP1 interrupt triggered.

' ICP1 Interrupt:
' In the ICP1 the Timer1 interrupt routine is set to 0 and increase the channel count by 1.
' Then the channel pulses are issued. Finally, will offer a status bits
' in the variable status flags (byte) set.

' If a start is detected, the channel counter (RC_ChannelNr) is set to 1.
' If no start signal is detected, the channel counter is incremented by 1. Thereafter, the
' selected channel (RC_ChannelNr) connected and the previously activated off.

' If more than 8 channels (PPM) are transmitted, the channel count is increased further.
' On the channel outputs but only a maximum of 8 channels are decoded.

' If less than 8 channels (PPM) are transmitted, the channel counter is displayed,
' And it will be produced at the outputs of any other stimulus.

' -----------------------------------------------
'               MCU - Configuration
' -----------------------------------------------

$regfile = "attiny44.dat"
$Crystal = 1000000                                          ' internal clock
$hwstack = 60
$swstack = 60
$framesize = 60


' -----------------------------------------------
'             Variables / Constants
' -----------------------------------------------

const RC_Frame = 2500                                       ' Threshold (counter value) for the detection of the start pulse (2.5 ms)
const RC_Timeout = 50000                                    ' Timeout for missing PPM-Signal (0,1s)

dim RC_ChannelNr as byte                                    ' current output channel

dim StatusFlags as byte                                     ' Status-Flags
    const ppm_FrameStart = 0                                ' New frame begins at the earliest edge
    const ppm_Trigger = 1                                   ' Trigger-edge (rising) an INT0
    const ppm_Timeout = 2                                   ' no edges of INT0

' -----------------------------------------------
'      Define Ports for channels 1 to 8
' -----------------------------------------------


' Name for the outputs
ddra = &b11111111                                           ' PortA.0 to PortA.7 as Output
RC_Channel1 Alias porta.0
RC_Channel2 Alias porta.1
RC_Channel3 Alias Porta.2
RC_Channel4 Alias Porta.3
RC_Channel5 Alias Porta.4
RC_Channel6 Alias Porta.5
RC_Channel7 Alias Porta.6
RC_Channel8 Alias Porta.7

' -----------------------------------------------
'       Ports configuration for LEDs
' -----------------------------------------------

' Red LED
LED_Error Alias Portb.0                                      ' LED indicator: no PPM signal to ICP1
config LED_Error = output
'LED_Error = 1                                               ' LED off

' Yellow LED
LED_Signal Alias Portb.1
config LED_Signal = output
'LED_Signal = 1                                              ' LED off

' -----------------------------------------------
'              Timer1 configuration 
' -----------------------------------------------

config timer1 = Counter , prescale = 1 , Clear timer = 1    ' Clock: 1000kHz
compare1b = RC_Frame                                        ' Frame-Detection (2,5ms)
compare1a = RC_Timeout                                      ' Timeout for no PPM-Signal (50ms)
start timer1

' -----------------------------------------------
'           Interrupts konfigurieren
' -----------------------------------------------

config INT0 = RISING                                        ' INT0 as PPM-Input (rising edge)
on int0 _ISR_INT0                                           ' Interrupt-Routine
enable int0                                                 ' Interrupt activated

on oc1a _ISR_OC1A                                           ' Frame-Timeout (50ms)
enable oc1a                                                 ' Frame-Interrupt enabled

on oc1b _ISR_OC1B                                           ' Frame-Detection (2,5ms)
enable oc1b                                                 ' Frame-Detection enabled

' Connected LEDs off after initialization
' (non-smart version)
wait 1
LED_Error = 1                                               ' Red LED off
waitms 500
LED_Signal = 1                                              ' Yellow LED off

enable interrupts                                           ' Global Interrupts enabled

' -----------------------------------------------
'         M A I N  L O O P
' -----------------------------------------------

do
    ' Evaluate Status flags

    ' LED-Error toggle on Frame-Timeout
    if StatusFlags.ppm_Timeout = 1 then
       toggle LED_Error                                     ' red LED to blink
       StatusFlags.ppm_Timeout = 0                          ' Flag reset
       LED_Signal = 1                                       ' LED-Signal on
    end if

    ' When detected trigger signals LED-off Error
    'and the LED signal is turned on permanently
    if StatusFlags.ppm_Trigger = 1 then                     ' Trigger pulses detected
        LED_Error = 1                                       ' Red LED Off
        StatusFlags.ppm_Trigger = 0
        LED_Signal = 0
    end if
loop

end



' -----------------------------------------------
'               Interrupt routines
' -----------------------------------------------

' Interrupt is called every negative edge at input ICP1

_ISR_INT0:

   Timer1 = 0                                               ' Timer1 set to 0

   incr RC_ChannelNr
   select case RC_ChannelNr                                 ' Channel - Pulse output
      case 1
         RC_Channel1 = 1                                    ' Channel 1 On
      case 2
         RC_Channel1 = 0                                    ' Channel 1 Off
         RC_Channel2 = 1                                    ' Channel 2 On                          
      case 3
         RC_Channel2 = 0                                    ' Channel 2 Off
         RC_Channel3 = 1                                    ' Channel 3 On
      case 4
         RC_Channel3 = 0                                    ' Channel 3 Off
         RC_Channel4 = 1                                    ' Channel 4 On
      case 5
         RC_Channel4 = 0                                    ' Channel 4 Off
         RC_Channel5 = 1                                    ' Channel 5 On
      case 6
         RC_Channel5 = 0                                    ' Channel 5 Off
         RC_Channel6 = 1                                    ' Channel 6 On
      case 7
         RC_Channel6 = 0                                    ' Channel 6 Off
         RC_Channel7 = 1                                    ' Channel 7 On
      case 8
         RC_Channel7 = 0                                    ' Channel 7 Off
         RC_Channel8 = 1                                    ' Channel 8 On
      case else
         RC_Channel8 = 0                                    ' Channel 8 Off
   end select
   StatusFlags.ppm_Trigger = 1                              ' Trigger edge is detected (rising INT0)
Return


' Frame Detection (Startpulse > 2,5ms)
_ISR_OC1B:
    RC_ChannelNr = 0                                        ' Channel counter to 0
    StatusFlags.ppm_FrameStart = 1                          ' Status flag new frame begins with the next edge
Return


' Timeout (no PPM-Signal; 50ms)
_ISR_OC1A:
    StatusFlags.ppm_Timeout = 1                             ' timeout within no PPM signal
Return