PPM decoding using 12F508 problem
I decoded a PPM signal from a old RC receiver with a shift register(HC595) with succes, but short noises cause random output on all channels , so was not a good ideea.
Also I tried to decode a PPM signal with my own code, but after a some work weeks I saw that is a disaster.
Finally I found a asm file made by BRUCE, work very stable but I need to make some changes .
Actually , the program have a fail safe, when input detect a bad pulses , each output go to initial start values. When input detect a bad pulses , I want to have 1,5 ms on each output.
Can somebody help me to modify the asm file , please? In asm I understant nothing ..(:
Here is BRUCE link : http://www.bhabbott.net.nz/decoder.html
Thx in advance!
Code:
;***************************************************************************
; rxdecode.asm Pulse Position Modulation Decoder for 4 Channel Rx
;***************************************************************************
; Bruce Abbott [email protected]
;
; for Microchip PIC 12C508, 12C509, 12F629 or 12F675.
;
;============================= Description =================================
;
; PPM DECODER:
;
; Each frame consists of 4 to 8 channels (5 to 9 pulses), followed by a sync
; gap. We only decode the first 4 channels.
;
; The width of each channel is 1 to 2mS (1.5mS when sticks centered). The
; sync gap is at least 2.5mS long, and frame length is approximately 20mS.
;
; The input signal should look something like this:-
;
; |<------------------ 1 frame (~20mS) -------------------->|
; |< 1~2mS >|
; _ _ _ _ _ _
; ___________| |_______| |______| |______| |______| |__ // ____________| |____
; sync gap ch1 ch2 ch3 ch4 etc. sync gap ch1
;
; NOTE: This waveform shows positive 'shift'. If your Rx outputs negative
; 'shift', the waveform is inverted.
;
; There is just enough time to generate four decoded outputs after receiving
; channel 4, and before the end of the sync gap.
;
; GLITCH FILTER:
;
; Each channel is averaged with the value from the previous frame, reducing
; servo jitter on weak signals. If any channel in a frame is corrupted, the
; whole frame is discarded and the last good frame is used instead.
;
; FAILSAFE:
;
; On receiving a sufficient number of good frames we save it for failsafe.
; Then, if the signal is corrupted for too long, we output the failsafe frame
; instead of the last good frame.
;
; THROTTLE ARMING:
;
; When entering failsafe the throttle is cut, and it will not be restarted
; until a good signal is detected AND the throttle is manually reset. This
; should prevent the situation where motor-induced RF interference causes
; the decoder to cycle in and out of failsafe repeatedly.
;
; For this feature to work the throttle channel has to be determined. Futaba
; and Hitec tranmitters assign the throttle to channel 3. JR, Airtronics and
; GWS use channel 1.
;
; Some ESC's need to have the throttle set to maximum at startup, perhaps to
; disable the brake or to enter programming mode. Therefore, channel 1 is
; designated as throttle if it measures less than 1.3mS or more than 1.7mS at
; startup, otherwise channel 3 is assumed.
;
; The throttle channel is forced to 1.05mS during failsafe, rather than set
; to its failsafe value, in case that value was full throttle!
;
; =============================================================================
; Summary of Changes
;
; 2003/12/2 V0.5 - Initial release
;
; 2003/12/27 V0.6 - ASM Error if 'addwf PCL' not in page 0.
; - Select processor via MPLab's Device Select menu.
; 2004/1/7 V0.7 - No output until failsafe frame captured. Should now be
; compatible with JR/GWS transmitters (throttle on CH1).
;
; 2004/1/9 V0.8 - Increased range to 0.75~2.28mS, now accepts >125% throws.
; Resolution is slightly reduced (from 5uS to 6uS).
; - Failsafe and Hold frames now use averaged output values.
; - Ignore missing 4th channel (for 3 channel TX) NOT TESTED!
;
; 2004/2/15 V0.9 - Fixed bug:- OSCCAL not initialized in 12F675 code!
; - Detect throttle channel. The throttle is held OFF after
; failsafe, until re-armed manually. This prevents cyling
; into and out of failsafe due to electrical noise coming
; from the motor.
;
; 2004/6/20 V1.0 - Using TMR0 to detect loss of signal. This prevents lockup
; during a clean signal loss (no noise) which may occur if
; used in a receiver which has muting.
; - TMR0 is also used to set frame repeat time in failsafe.
; - Fixed bug:- Initial channel output values were wrong.
;
; 2004/10/24 V1.1 - Positive and Negative shift versions.
; - Ignore short glitches on signal transitions.
; - Ensure throttle is low in failsafe, even if it was maxiumum
; at startup (possible requirement for ESC programming).
;
; 2004/12/12 V1.2 - Fixed bug: JR throttle arming was disabled due to a typo!
;
; 2005/1/20 V1.3 - Now accepts pulse widths from 180uS to 700uS.
;
; -----------------------------------------------------------------------------
#DEFINE version "1.3"
#DEFINE ARM_THROTTLE ; enable if throttle arming control wanted.
#DEFINE DETECT_JR ; enable for JR/Airtronics/GWS throttle detection.
;#DEFINE Negative_Shift ; enable for Futaba/Hitec on 72MHz
; Make sure that PROCESSOR and <include> file are compatible with your CPU!
; 12C508(A) and 12C509(A) can use 12C508 definitions. 12F629 can use 12F675
; definitions (just don't try to use the A/D module...)
;#DEFINE __12C508 ; enable if processor not specified elsewhere
;#DEFINE __12F675 ; (MPLAB:- use menu <Configure/Select_Device>)
;#DEFINE NO_OSCCAL ; enable if OSCCAL value was erased!
ifdef __12C508
PROCESSOR PIC12C508
INCLUDE <P12C508.inc>
__CONFIG _MCLRE_OFF&_CP_OFF&_WDT_ON&_IntRC_OSC
else
PROCESSOR PIC12F675
INCLUDE <P12F675.inc>
__CONFIG _MCLRE_OFF&_CP_OFF&_WDT_ON&_BODEN_ON&_INTRC_OSC_NOCLKOUT
endif
radix dec
errorlevel 0,-305,-302
; Bit definitions for the GPIO register and the TRIS register
#DEFINE CH_1 0 ; pin 7 Channel 1 output
#DEFINE CH_2 1 ; pin 6 Channel 2 output
#DEFINE CH_3 2 ; pin 5 Channel 3 output
#DEFINE PPM_in 3 ; pin 4 input pulse stream
#DEFINE CH_4 4 ; pin 3 Channel 4 Output
#DEFINE LED 5 ; pin 2 Signal Indicator LED
#DEFINE TrisBits H'FF'&~((1<<CH_1)|(1<<CH_2)|(1<<CH_3)|(1<<CH_4)|(1<<LED))
; Bits to be set with the OPTION instruction
; No wake up
; No weak pullups
; Timer 0 source internal
; Prescaler to Timer 0, divide by 256.
;
#DEFINE OptionBits B'11000111'
; =========================================================================
; Macro for generating short time delays
;
NO_OP MACRO count
NO_OP_COUNT SET count
WHILE NO_OP_COUNT>1
goto $+1 ; 2 clocks
NO_OP_COUNT SET NO_OP_COUNT-2
ENDW
IF NO_OP_COUNT
nop ; 1 clock
ENDIF
ENDM
;===========================================================================
; Macro to create offsets for variables in RAM
;
ifdef __12C508
ByteAddr SET 7
else
ByteAddr SET 32 ; user RAM starts here
endif
BYTE MACRO ByteName
ByteName EQU ByteAddr
ByteAddr SET ByteAddr+1
ENDM
; ==========================================================================
; RAM Variable Definitions
;
BYTE Flags ; various boolean flags
BYTE PPMcount ; pulse length. 1~255 = 0.75~2.28mS
BYTE PPM_1 ; channel 1 in
BYTE PPM_2 ; channel 2 in
BYTE PPM_3 ; channel 3 in
BYTE PPM_4 ; channel 4 in
BYTE PWM_1 ; channel 1 out
BYTE PWM_2 ; channel 2 out
BYTE PWM_3 ; channel 3 out
BYTE PWM_4 ; channel 4 out
BYTE PMM_1 ; channel 1 memory
BYTE PMM_2 ; channel 2 memory
BYTE PMM_3 ; channel 3 memory
BYTE PMM_4 ; channel 4 memory
BYTE FLS_1 ; channel 1 failsafe
BYTE FLS_2 ; channel 2 failsafe
BYTE FLS_3 ; channel 3 failsafe
BYTE FLS_4 ; channel 4 failsafe
BYTE GoodFrames ; No. of good frames to go before
; accepting failsafe frame.
BYTE HoldFrames ; No. of bad frames to go before going
; to failsafe
BYTE ArmFrames ; No. of low throttle frames to go
; before arming throttle.
BYTE Temp1
BYTE Temp2
; flag values
;
#DEFINE WATCH 0 ; Watchdog timeout
#DEFINE GOT_FS 1 ; have captured failsafe frame
#DEFINE GOT_4 2 ; 4 channels found in current frame
#DEFINE DET_4 3 ; 4 channel TX detected
#DEFINE JR 4 ; JR throttle detected
#DEFINE ARMED 5 ; throttle armed
; number of consecutive good frames required at startup.
#DEFINE GOODCOUNT 10
; number of consecutive bad frames accepted without going to failsafe.
#DEFINE HOLDCOUNT 25
; number of consecutive low throttle frames required before arming.
#DEFINE ARMCOUNT 10
; macros for working with negative or positive shift
skip_PPM_high MACRO
ifdef Negative_Shift
btfsc GPIO,PPM_in
else
btfss GPIO,PPM_in
endif
ENDM
skip_PPM_low MACRO
ifdef Negative_Shift
btfss GPIO,PPM_in
else
btfsc GPIO,PPM_in
endif
ENDM
;****************************************************************************
; Code
;
ORG 0
goto ColdStart
;-------------------------- version string ----------------------------------
org 8
ifdef __12C508
dt "RXDEC508"
endif
ifdef __12F629
dt "RXDEC629"
endif
ifdef __12F675
dt "RXDEC675"
endif
dt "--V"
dt version
dt "--"
ifdef ARM_THROTTLE
dt "ARMTHROT"
endif
ifdef DETECT_JR
dt "DETECTJR"
endif
ifdef Negative_Shift
dt "NEG_SHFT"
endif
;============================================================================
ColdStart:
bcf Flags,WATCH
btfss STATUS,NOT_TO ; copy Watchdog timeout flag
bsf Flags,WATCH
; get oscillator calibration value and use it to fine-tune clock frequency.
; 12C508/9 has value in W at startup, 12F629/75 gets it from RETLW at 0x3ff.
ifdef __12C508
ifdef NO_OSCCAL
movlw 0x90 ; replace with value for your PIC!
endif
movwf OSCCAL ; set oscillator calibration
else
bsf STATUS,RP0 ; register bank 1 (12F629/75)
call 0x3ff ; get OSCCAL value
movwf OSCCAL ; set oscillator calibration
bcf STATUS, RP0 ; register bank 0
endif
ifdef __12C508
clrwdt
movlw OptionBits
OPTION
else
clrwdt
bsf STATUS,RP0 ; register bank 1 (12F629/75)
movlw OptionBits
movwf OPTION_REG
bcf STATUS,RP0 ; register bank 0
clrwdt
endif
; initialise I/O registers
ifdef __12C508
clrf GPIO ; all outputs low
movlw TrisBits
TRIS GPIO ; set I/O pin directions
else
clrf GPIO ; all outputs low
bsf STATUS,RP0 ; register bank 1 (12F629/75)
movlw TrisBits
movwf TRISIO ; set I/O pin directions
ifdef ANSEL
clrf ANSEL ; disable analog inputs (12F675)
endif
bcf STATUS,RP0 ; register bank 0
movlw b'00000111'
movwf CMCON ; Comparator off
endif
; CPU specific stuff done, now we can start the main program!
goto Main
;----------------------------------------------------------------------------
; GetPPM: Get time to next PPM pulse
;----------------------------------------------------------------------------
;
; input: PPM signal has just gone high.
; output: PPMcount = Pulse Width * 6uS, next pulse has started
; error: PPMcount = XX and error code in W.
;
; Error Codes
; 0 = good channel
; 1 = pulse too short, too long, or next pulse too soon
; 2 = no next pulse (ie. no channel)
PRECHARGE = ((750-15)/6) ; = 0.75mS
GetPPM:
movlw PRECHARGE ; preset count for signal high length
movwf PPMcount
movlw (30/6)
movwf Temp1
high_delay: NO_OP 2
decf PPMcount ; wait 30uS to skip short glitches
decfsz Temp1
goto high_delay
hiloop:
skip_PPM_high ; signal gone low ?
goto pulselo
nop ; 6uS per loop
decfsz PPMcount ; count down
goto hiloop
retlw 1 ; timed out, signal high
pulselo:
movlw PRECHARGE-(180/6)
subwf PPMcount,W
skpnc ; less than minimum pulse width ?
retlw 1
movlw PRECHARGE-(700/6)
subwf PPMcount,W
skpc ; greater than maximum pulse width ?
retlw 1
movlw (30/6)
movwf Temp1
low_delay: NO_OP 2
decf PPMcount ; wait 30uS to skip short glitches
decfsz Temp1
goto low_delay
to750uS:
skip_PPM_low ; signal should stay low until 0.75mS
retlw 1
nop ; 6uS per loop
decfsz PPMcount ; count down to zero @ 0.75mS
goto to750uS
incf PPMcount ; count up, start at 1
to2280uS:
skip_PPM_low ; start of next channel pulse ?
retlw 0 ; return OK
nop ; 6uS per loop
incfsz PPMcount ; count up to 256 @ 2.28mS
goto to2280uS
retlw 2 ; return timeout error @ 2.28mS
;------------------------------------------------------------------------------
; Output PPM widths to channels 1-4
;------------------------------------------------------------------------------
Output:
movf PWM_1,W ; get pulse length
bsf GPIO,CH_1 ; start pulse
call Servo_Delay ; delay 6uS*len
bcf GPIO,CH_1 ; finish pulse
movf PWM_2,W
bsf GPIO,CH_2
call Servo_Delay
bcf GPIO,CH_2
movf PWM_3,W
bsf GPIO,CH_3
call Servo_Delay
bcf GPIO,CH_3
movf PWM_4,W
bsf GPIO,CH_4
call Servo_Delay
bcf GPIO,CH_4
retlw 0
;------------------------------------------------------------------------------
; Delay Timer for Output Pulse
;------------------------------------------------------------------------------
;
; input: W=delay count, 1 to 255 = 0.75 to 2.28mS
;
Servo_Delay:
movwf Temp2
movlw (750-6)/6
movwf Temp1
_ds1: nop
clrwdt
nop
decfsz Temp1 ; wait 750uS
goto _ds1
_ds2: nop
clrwdt
nop
decfsz Temp2 ; wait 0~1.53mS, total = 0.75~2.28mS
goto _ds2
retlw 0
;-------------------------------------------------------------------------------
; Millisecond Delay Timer
;-------------------------------------------------------------------------------
; Input: W = number of milliseconds to wait (max 256mS)
;
dx1k: movwf Temp1
_dx1k1: movlw (1000-5)/5
movwf Temp2
_dx1k2: clrwdt ; avoid watchdog timeout
nop
decfsz Temp2 ; wait 1mS
goto _dx1k2
decfsz Temp1
goto _dx1k1
retlw 0
;*******************************************************************************
; Main
;*******************************************************************************
Main: btfsc Flags,WATCH ; did the watchdog timeout ?
goto Failsafe ; oops! try to keep going ...
clrf Flags ; clear all flags
movlw 250 ; wait 500mS for Rx to stabilise
call dx1k ; (signal LED is on)
movlw 250
call dx1k
Start: bsf GPIO,LED ; signal LED off
movlw (1500-750)/6
movwf PMM_1
movwf PMM_2 ; all channel outputs at midpoint
movwf PMM_3
movwf PMM_4
movwf PPM_4 ; init channel 4 (for 3 channel TX)
movlw GOODCOUNT ; set number of good frames required
movwf GoodFrames ; before saving failsafe values.
movlw HOLDCOUNT ; set number of bad frames allowed
movwf HoldFrames ; before going to failsafe.
movlw ARMCOUNT ; set number of low throttle frames
movwf ArmFrames ; before arming throttle
goto no_signal
Failsafe: movlw 1
movwf HoldFrames ; stay in failsafe until signal returns
btfss Flags,GOT_FS ; do we have good failsafe values?
goto no_signal
movf FLS_1,W
movwf PWM_1
movf FLS_2,W ; get failsafe values
movwf PWM_2
movf FLS_3,W
movwf PWM_3
movf FLS_4,W
movwf PWM_4
call Output ; output failsafe frame
bcf Flags,ARMED ; keep throttle OFF
movlw ARMCOUNT
movwf ArmFrames ; reset throttle arming delay
no_signal: bsf GPIO,LED ; signal LED off
wait_sync: clrwdt ; we're still sane, no reset please!
clrf Temp1
movlw 9 ; set 'gap detect' timeout to 23mS
movwf Temp2
wait_gap: skip_PPM_high ; wait for a gap ]
goto time_gap ; ]
nop ; ]
clrwdt ; ]
nop ; ] 10uS per loop
decf Temp1 ; ]
skpnz ; ]
decfsz Temp2 ; timed out ? ]
goto wait_gap ; ]
goto badframe ; can't find sync gap!
time_gap: clrf PPMcount ; reset gap timer
in_gap: decf Temp1 ; }
skpnz ; }
decf Temp2 ; timed out ? }
skpnz ; }
goto badframe ; can't find sync gap! } 10uS per loop
skip_PPM_low ; still in gap ? }
goto wait_gap ; }
incfsz PPMcount ; gap > 2.56mS ? }
goto in_gap ; no, continue timing }
Get_Frame: movlw 128-(23000/256) ; set frame timeout to 23mS
movwf TMR0
wait_1st: clrwdt
btfsc TMR0,7 ; timer reached 23mS ?
goto badframe
skip_PPM_high ; wait for start of first channel
goto wait_1st
bcf Flags,GOT_4 ; channel 4 not received yet
NO_OP 3
call GetPPM ; get first channel
andlw 255
skpz ; process return code
goto badframe
movf PPMcount,W
movwf PPM_1
call GetPPM ; get 2nd channel
andlw 255
skpz
goto badframe
movf PPMcount,W
movwf PPM_2
call GetPPM ; get 3rd channel
andlw 255
skpz
goto badframe
movf PPMcount,W
movwf PPM_3
call GetPPM ; get 4th channel
andlw 255
skpz
goto error4
movf PPMcount,W
movwf PPM_4
bsf Flags,GOT_4
goto update
error4: xorlw 2
skpz ; channel 4 missing ?
goto badframe
btfss Flags,GOT_FS ; got failsafe frame yet ?
goto update ; no, ignore missing channel 4
btfss Flags,DET_4 ; 4 channels detected ?
goto update ; no, ignore missing channel 4
badframe: clrwdt
movlw 128-((23000-9000)/256); timer reached 9mS ?
subwf TMR0,w
skpc ; wait 9mS to skip other channels
goto badframe
movlw ARMCOUNT ; reset throttle arming delay
movwf ArmFrames
decfsz HoldFrames ; too many bad frames ?
goto hold
goto Failsafe
hold: btfsc Flags,GOT_FS ; good frame available for hold ?
call Output ; yes, output last good frame
goto no_signal ; no, just stay silent
;
; Got a good frame. Output the averaged pulse widths of this frame
; and the last frame.
;
update: movf PPM_1,W
addwf PMM_1 ; PWM out = average(this+last)
rrf PMM_1,w
movwf PWM_1
movf PPM_2,W
addwf PMM_2
rrf PMM_2,w
movwf PWM_2
movf PPM_3,W
addwf PMM_3
rrf PMM_3,w
movwf PWM_3
movf PPM_4,W
addwf PMM_4
rrf PMM_4,w
movwf PWM_4
btfss Flags,GOT_FS ; no output until failsafe captured
goto output_done
ifdef ARM_THROTTLE
btfsc Flags,ARMED ; throttle armed ?
goto do_output ; yes
movlw (1300-750)/6
btfsc Flags,JR
subwf PWM_1,w ; throttle < 1.3mS ?
btfss Flags,JR
subwf PWM_3,w
skpc
goto low_throttle ; yes
movlw ARMCOUNT
movwf ArmFrames ; no, reset arming delay
goto disarm
low_throttle: decfsz ArmFrames ; got enough arming frames ?
goto disarm
bsf Flags,ARMED ; yes, arm throttle now
goto do_output
disarm:
movf FLS_3,w
btfss Flags,JR
movwf PWM_3 ; set throttle to failsafe value
movf FLS_1,w
btfsc Flags,JR
movwf PWM_1
endif ; ARM_THROTTLE
do_output: call Output ; output good frame
output_done: movf PPM_1,W
movwf PMM_1
movf PPM_2,W ; remember this frame
movwf PMM_2
movf PPM_3,W
movwf PMM_3
movf PPM_4,W
movwf PMM_4
movlw HOLDCOUNT ; reset failsafe timeout
movwf HoldFrames
bcf GPIO,LED ; signal LED on
btfsc Flags,GOT_FS ; already got failsafe frame ?
goto frame_done ; yes
clrwdt
decfsz GoodFrames ; got enough good frames ?
goto frame_done ; no
; Got enough good frames, now get failsafe values
btfsc Flags,GOT_4 ; channel 4 detected ?
bsf Flags,DET_4
movf PWM_1,W
movwf FLS_1
movf PWM_2,W
movwf FLS_2
movf PWM_3,W ; copy good output to failsafe
movwf FLS_3
movf PWM_4,W
movwf FLS_4
bsf Flags,GOT_FS ; failsafe frame captured
ifdef ARM_THROTTLE
ifdef DETECT_JR
movlw (1300-750)/6
subwf FLS_1,w ; channel 1 < 1.3mS ?
skpc
goto jr_detected
movlw (1700-750)/6
subwf FLS_1,w ; channel 1 >= 1.7mS ?
skpc
goto futaba
movlw (1100-750)/6 ; failsafe low throttle!
movwf FLS_1
jr_detected: bsf Flags,JR ; JR throttle detected
goto arm
endif ; DETECT_JR
futaba: movlw (1700-750)/6
subwf FLS_3,w ; channel 3 >= 1.7mS ?
skpc
goto arm
movlw (1100-750)/6 ; failsafe low throttle!
movwf FLS_3
arm: bsf Flags,ARMED ; arm throttle now
endif ; ARM_THROTTLE
frame_done: goto wait_sync ; wait for next frame
;---------- Oscillator Calibration Subroutine (12F629/75 only) --------------
ifdef __12F675
org 0x3ff
retlw 0x90 ; replace with oscal value for your PIC!
endif
END
Re: PPM decoding using 12F508 problem
I think this will work.
changed last label to Failsafeb
Code:
badframe: clrwdt
movlw 128-((23000-9000)/256); timer reached 9mS ?
subwf TMR0,w
skpc ; wait 9mS to skip other channels
goto badframe
movlw ARMCOUNT ; reset throttle arming delay
movwf ArmFrames
decfsz HoldFrames ; too many bad frames ?
goto hold
goto Failsafeb
then try this directly above the routine Failsafe
Code:
Failsafeb:
bsf GPIO,CH_1
bsf GPIO,CH_2
bsf GPIO,CH_3
bsf GPIO,CH_4
movlw 1 ;total 1.5ms
call Servo_Delay
movlw 1
call Servo_Delay
;goto Failsafe ; not needed because execution will continue to Failsafe
I can’t guess if you want to turn throttle off before or after the 1.5ms,
or when you want to reset throttle arming delay which was done in Failsafe.
That turns all outputs on 1 instruction apart.
If you meant cycle them all with 1.5 ms delay each, then ignore all of the above,
and simply write your own delay constants in the original routine instead of copying
from the variables.
This flows onto the next label int he program so must be left in place.
Code:
Failsafe: movlw 1
movwf HoldFrames ; stay in failsafe until signal returns
btfss Flags,GOT_FS ; do we have good failsafe values?
goto no_signal
movlw 110 ; only guessing approx value for 1.5ms here
movwf PWM_1
movlw 110
movwf PWM_2
movlw 110
movwf PWM_3
movlw 110
movwf PWM_4
call Output ; output failsafe frame
bcf Flags,ARMED ; keep throttle OFF
movlw ARMCOUNT
movwf ArmFrames ; reset throttle arming delay
Re: PPM decoding using 12F508 problem
Thank you very much Art ! All its ok, now is working perfectly.
I adjusted the value, now the pulse on all chanells have 1,5mS
Code:
movlw 125 ; value for 1.5ms here
movwf PWM_1
movlw 125
movwf PWM_2
movlw 125
movwf PWM_3
movlw 125
movwf PWM_4
