One Wire Serial Communication using Teensy 4 with SRXL2 Spektrum Receivers

[xdog12]

I have a Spektrum SRXL2 Serial Receiver that I want to connect to a Teensy 4. I have an example for arduino that I want to convert to one-wire communication. How do I take this Serial communication code and use the OneWire Library instead.

This is the documentation for SRXL2 https://github.com/SpektrumRC/SRXL2

I'm using this example code to communicate with the receiver.
https://github.com/AndersHoglund/Ard...oPwmBridge.ino

/* 
 *  Spektrum SRXL2 to PWM Bridge
 */
//#define USE_SOFTWARE_SERIAL

#include <Servo.h>
#ifdef USE_SOFTWARE_SERIAL
#include <SoftwareSerial.h>
#endif

#include "spm_srxl.h"

// Select SRXL2 input and output pins (need to be combined into one halfduplex line with a diod)

#ifdef USE_SOFTWARE_SERIAL
#define SRXL2_INPUT_PIN 2     //  -------o--------- SRXL2_DATA
                              //         |
#define SRXL2_OUTPUT_PIN 3    //  ---<|---
#else
//Hardware UART might also need some pullup
                              // VCC +--|===|--
                              //              |
#define SRXL2_INPUT_PIN 1     //  ------------o--------- SRXL2_DATA
                              //              |
#define SRXL2_OUTPUT_PIN 0    //  ---<|--------
#endif

#define SRXL2_PORT_BAUDRATE_DEFAULT 115200
#define SRXL2_FRAME_TIMEOUT 22 

// Spektrum channel order
#define THRO 0
#define AILE 1
#define ELEV 2
#define YAW  3
#define GEAR 4
#define AUX1 5
#define AUX2 6
#define AUX3 7
#define AUX4 8
#define AUX5 9

// Only available at 22ms frame rate.
#define AUX6 10
#define AUX7 11

// Select the PWM output pins
#define PWM_THRO_PIN 9
#define PWM_AUX2_PIN 8
#define PWM_AUX3_PIN 7
#define PWM_AUX4_PIN 6
#define PWM_AUX5_PIN 5

typedef struct
{
  int channel;
  int pin;
  int value;
  unsigned long prevTime;
  Servo device;
} pwm_t;

pwm_t pwms[] =
{
  {THRO, PWM_THRO_PIN, 1000, 0},
  {AUX2, PWM_AUX2_PIN, 1500, 0},
  {AUX3, PWM_AUX3_PIN, 1500, 0},
  {AUX4, PWM_AUX4_PIN, 1500, 0},
  {AUX5, PWM_AUX5_PIN, 1500, 0}
};

#ifdef USE_SOFTWARE_SERIAL
SoftwareSerial srxl2port(SRXL2_INPUT_PIN, SRXL2_OUTPUT_PIN); // RX, TX
#else
#define srxl2port Serial
#endif

unsigned long currentTime;
unsigned long prevPwmTime = 0;
const long pwmInterval = 22;

void setup()
{ 
  srxl2port.begin(SRXL2_PORT_BAUDRATE_DEFAULT);
    
  srxlInitDevice(SRXL_DEVICE_ID, SRXL_DEVICE_PRIORITY, SRXL_DEVICE_INFO, 0x01000001);// // Init the local SRXL device with the unique ID 32 bit 0x01000001 hexadezimal.
  srxlInitBus(0, 1, SRXL_SUPPORTED_BAUD_RATES);// Init the SRXL bus: The bus index must always be < SRXL_NUM_OF_BUSES -- in this case, it can only be 0 since we have only 1 bus.

  for (int i=0; i < sizeof(pwms)/sizeof(pwm_t); i++ )
  {
    pwms[i].device.attach(pwms[i].pin);
  }
}

void loop()
{
  currentTime = millis();

  static unsigned long prevSerialRxTime = 0;

  // UART receive buffer
  static uint8_t rxBuffer[2 * SRXL_MAX_BUFFER_SIZE];
  static uint8_t rxBufferIndex = 0;

  if (currentTime - prevSerialRxTime > SRXL2_FRAME_TIMEOUT)
  {
    prevSerialRxTime = currentTime;
    rxBufferIndex = 0;
    srxlRun(0, SRXL2_FRAME_TIMEOUT);
  }

  if ( srxl2port.available() )
  {
    prevSerialRxTime = currentTime;
    unsigned char c = srxl2port.read(); // 
    rxBuffer[rxBufferIndex++] = c;
  }

  if (rxBufferIndex >= 5)
  {
    if(rxBuffer[0] == SPEKTRUM_SRXL_ID)
    {
      uint8_t packetLength = rxBuffer[2];
      if (rxBufferIndex >= packetLength)
      {
        // Try to parse SRXL packet -- this internally calls srxlRun() after packet is parsed and reset timeout
        if (srxlParsePacket(0, rxBuffer, packetLength))
        {
          // Move any remaining bytes to beginning of buffer (usually 0)
          rxBufferIndex -= packetLength;
          memmove(rxBuffer, &rxBuffer[packetLength], rxBufferIndex);
        }
        else
        {
            rxBufferIndex = 0;
        }
      }
    }
  }

  for (int i=0; i < sizeof(pwms)/sizeof(pwm_t); i++ )
  {   
    currentTime = millis();
    if (currentTime - pwms[i].prevTime >= pwmInterval)
    {
      pwms[i].prevTime = currentTime;
      pwms[i].device.writeMicroseconds(pwms[i].value);
    }
  }    
}

///////////////////////// SRXL2 channel interface //////////////////////////////

void userProvidedReceivedChannelData(SrxlChannelData* pChannelData, bool isFailsafe)
{
  for (int i=0; i < sizeof(pwms)/sizeof(pwm_t); i++ )
  {   
    // Get channel value and convert to 988 - 1500 - 2011 pwm range
    pwms[i].value = 988 + srxlChData.values[pwms[i].channel] >> 6;    // 16-bit to 10-bit range (0 - 1023)
  }
}

void uartSetBaud(uint8_t uart, uint32_t baudRate) // Automatic adjust SRXL2 baudrate. 
{
  // Not supported yet
}

void uartTransmit(uint8_t uart, uint8_t* pBuffer, uint8_t length)
{
  for (uint8_t i=0; i < length; i++)
  {
    srxl2port.write(pBuffer[i]);
  }
  srxl2port.flush();
}

[rcarr]

If you look at the one-wire protocol, you will see it is completely different from half duplex serial ( rs232 type ) communication. You will not be able to use the OneWire Library.

[xdog12]

Srlx2 uses one wire, the example code that I posted uses a diode to combine the tx/rx lines of the Arduino. Are you saying that the one wire library is unable to communicate with the receiver using Srlx2 protocol?

I posted the example code to show the necessary call and response to communicate with SRXL2 receivers. I don't understand why one wire can't be used to listen and respond to the SRXL2 receiver.

[rcarr]

To convert your code to Teensy could be as simple as changing one line:

#define srxl2port Serial
 Change this line to
#define srxl2port Serial1

You would then add the diode circuit to enable the half duplex feature. You would wire to pins 0 and 1 to use Serial1. If your receiver is 5 volt, then you may need logic level converters, you need to check/measure with a voltmeter; but it is probably open collector logic and in that case you would just add a pullup to 3.3 volts.

OneWire is a completely different protocol from Serial Uarts.


Edit: took a quick look at the Spec at one of your links, it says the Tx/Rx signal is 3.3 volt with a very weak pullup. So you won't need logic level converters but may need a pullup.

[xdog12]

I get this error when I try to run this code, but I don't know how to solve it. Thank you.

cannot convert 'PORTDemulation*' to 'volatile uint8_t* {aka volatile unsigned char*}' in initialization

//////////////////////////////////////////////////////////////////////////////////////////////////////
//
// SRXL2 decoder example for Base Receivers and ATMega328P. Used receiver in this exampel is the AR6610T.
// Channels are locked to these pins:
// Ch0=Pin2, Ch1=Pin3, Ch2=Pin4, Ch3=Pin5, Ch4=Pin6, Ch5=Pin7, Ch6=Pin8, Ch7=Pin9, Ch8=Pin10, Ch9=Pin11
// Ch10=Pin12, Ch11=Pin13, (Ch12=PinA0, Ch13=PinA1, Ch14=PinA2, Ch15=PinA3, Ch16=PinA4, Ch17=PinA5)
//
// 
//////////////////////////////////////////////////////////////////////////////////////////////////////

#include <avr/interrupt.h>
#include <avr/wdt.h>//watchdog
#include "spm_srxl.h"

#define SRXL2_PORT_BAUDRATE_DEFAULT 115200
#define SRXL2_FRAME_TIMEOUT 22
#define srxl2port Serial1
#define NO_OF_INPUT_CHANNELS 18
#define NO_OF_OUTPUT_CHANNELS 18
#define MAX_NO_OF_CHANNELS 20
const uint8_t c=8;//Anzahl PWM Kanäle der Empfänger hat.AR6600 T= 6 AR8020T = 8 etc. 0 for remotes (recommend only 4650 or 4651) 
// Number of PWM channels the receiver has. AR6600T= 6 AR8020T = 8 etc.

#if (NO_OF_OUTPUT_CHANNELS > MAX_NO_OF_CHANNELS)
error
#endif

// Spektrum channel order
#define THRO 0
#define AILE 1
#define ELEV 2
#define YAW  3
#define GEAR 4
#define AUX1 5
#define AUX2 6
#define AUX3 7
#define AUX4 8
#define AUX5 9

// Only available at 22ms frame rate.
#define AUX6 10
#define AUX7 11

// X-Plus channels, non DX18 mode.
#define X1 12
#define X2 13
#define X3 14
#define X4 15
#define X5 16
#define X6 17
#define X7 18
#define X8 19

#define DSMX_2K_LOW     341  // -100%
#define DSMX_2K_CENTER 1024  //    0%
#define DSMX_2K_HIGH   1706  // +100%
#define DSMX_2K_OFFSET 8991
 
#define YES 1
#define NO 0
#define UseJitterCompensation YES

unsigned long currentTime;
unsigned long prevPwmTime = 0;
const long pwmInterval = 22;

boolean validServoPacket   = false;
boolean timersRunning = false;

// Array to store the input PWM servo position

uint8_t inputChannelMap[NO_OF_INPUT_CHANNELS] = {THRO, AILE, ELEV, YAW, GEAR, AUX1, AUX2, AUX3, AUX4,  AUX5, AUX6, AUX7, X3, X4, X5, X6, X7, X8};

static byte Jitter;
static byte Jitter2;
static byte Jitter3;
static byte Jitter4;

static uint8_t iCount;
static volatile uint8_t *OutPortTable[MAX_NO_OF_CHANNELS] = {&PORTD,&PORTD,&PORTD,&PORTD,&PORTD,&PORTD,&PORTB,&PORTB,&PORTB,&PORTB,&PORTB,&PORTB,&PORTC,&PORTC,&PORTC,&PORTC,&PORTC,&PORTC,&PORTC,&PORTC};
static uint8_t OutBitTable[MAX_NO_OF_CHANNELS] = {4,8,16,32,64,128,1,2,4,8,16,32,1,2,4,8,16,32,64,128};
static uint16_t ServoPW[MAX_NO_OF_CHANNELS];
static uint8_t Timer2Toggle;
static volatile uint8_t *OutPort1A = &PORTD;
static volatile uint8_t *OutPort1B = &PORTB;
static uint8_t OutBit1A = 0;
static uint8_t OutBit1B = 0;
static volatile uint8_t *OutPortNext1A = &PORTD;
static volatile uint8_t *OutPortNext1B = &PORTB;
static uint8_t OutBitNext1A = 0;
static uint8_t OutBitNext1B = 0;

void setup()
{
  initServoOutputs();
  
  srxl2port.begin(SRXL2_PORT_BAUDRATE_DEFAULT);
  srxlInitDevice(SRXL_DEVICE_ID, SRXL_DEVICE_PRIORITY, SRXL_DEVICE_INFO, 0x01A12024);// When you use more as one expander on the same srxl2 bus need every expander a Unique ID!
  srxlInitBus(0, 1, SRXL_SUPPORTED_BAUD_RATES);

  wdt_enable(WDTO_250MS);   // Set watchdog to 0.25 s and start.
}

void loop() {
  currentTime = millis();

  static unsigned long prevSerialRxTime = 0;

  // UART receive buffer
  static uint8_t rxBuffer[2 * SRXL_MAX_BUFFER_SIZE];
  static uint8_t rxBufferIndex = 0;

  if (currentTime - prevSerialRxTime > SRXL2_FRAME_TIMEOUT)
  {
    prevSerialRxTime = currentTime;
    rxBufferIndex = 0;
    srxlRun(0, SRXL2_FRAME_TIMEOUT);
  }

  if ( srxl2port.available() )
  {
    prevSerialRxTime = currentTime;
    unsigned char c = srxl2port.read(); // 
    rxBuffer[rxBufferIndex++] = c;
  }

  if (rxBufferIndex >= 5)
  {
    if(rxBuffer[0] == SPEKTRUM_SRXL_ID)
    {
      uint8_t packetLength = rxBuffer[2];
      if (rxBufferIndex >= packetLength)
      {
        // Try to parse SRXL packet -- this internally calls srxlRun() after packet is parsed and reset timeout
        if (srxlParsePacket(0, rxBuffer, packetLength))
        {
          // Move any remaining bytes to beginning of buffer (usually 0)
          rxBufferIndex -= packetLength;
          memmove(rxBuffer, &rxBuffer[packetLength], rxBufferIndex);
        }
        else
        {
            rxBufferIndex = 0;
        }
      }
    }
  }

  if (currentTime - prevPwmTime >= pwmInterval)
  {
    prevPwmTime = currentTime;
    
    //PPM();                                  // Do servo move
    if (validServoPacket && (!timersRunning)) ServoSetup();
  }
}

volatile void PPM() //Move servos every 22ms to the desired position.
{
  
  if (validServoPacket && (!timersRunning)) ServoSetup();
}

ISR(TIMER1_COMPA_vect) // Interrupt routine for timer 1 compare A. Used for timing each pulse width for the servo PWM.
{ 
#if UseJitterCompensation == YES
    Jitter = TCNT1 - OCR1A;
    if(Jitter == 32){asm volatile("nop\n\tnop\n\tnop\n\tnop\n\tnop\n\t");}
    if(Jitter == 31){asm volatile("nop\n\tnop\n\tnop\n\t");}
    if(Jitter == 30){asm volatile("nop\n\t");}
    if(Jitter == 29){asm volatile("nop\n\t");}
#endif
  *OutPort1A &= ~OutBit1A;                //Pulse A finished. Set to low
}

ISR(TIMER1_COMPB_vect) // Interrupt routine for timer 1 compare B. Used for timing each pulse width for the servo PWM.
{ 
#if UseJitterCompensation == YES
    Jitter2 = TCNT1 - OCR1B;
    if(Jitter2 == 32){asm volatile("nop\n\tnop\n\tnop\n\tnop\n\tnop\n\t");}
    if(Jitter2 == 31){asm volatile("nop\n\tnop\n\tnop\n\t");}
    if(Jitter2 == 30){asm volatile("nop\n\t");}
    if(Jitter2 == 29){asm volatile("nop\n\t");}
#endif
  *OutPort1B &= ~OutBit1B;                //Pulse B finished. Set to low
}

ISR(TIMER2_COMPA_vect) // Interrupt routine for timer 2 compare A. Used for timing 50Hz for each servo.
{ 
#if UseJitterCompensation == YES
    Jitter4 = TCNT1L-100;
    if(Jitter4 == 118){asm volatile("nop\n\tnop\n\tnop\n\tnop\n\tnop\n\tnop\n\tnop\n\t");}
    if(Jitter4 == 117){asm volatile("nop\n\tnop\n\tnop\n\tnop\n\tnop\n\t");}
    if(Jitter4 == 116){asm volatile("nop\n\tnop\n\tnop\n\t");}
    if(Jitter4 == 115){asm volatile("nop\n\t");}
    if(Jitter4 == 114){asm volatile("nop\n\t");}
#endif
  *OutPortNext1A |= OutBitNext1A;         // Start new pulse on next servo. Write pin HIGH
  *OutPortNext1B |= OutBitNext1B;         // Start new pulse on next servo. Write pin HIGH
}

ISR(TIMER2_COMPB_vect) // Interrupt routine for timer 2 compare B. Used for timing 50Hz for each servo.
{ 
  TIFR1 = 255;                                       // Clear  pending interrupts
#if UseJitterCompensation == YES
    Jitter3 = TCNT1L-100;
    if(Jitter3 == 137){asm volatile("nop\n\tnop\n\tnop\n\tnop\n\tnop\n\tnop\n\tnop\n\t");}
    if(Jitter3 == 136){asm volatile("nop\n\tnop\n\tnop\n\tnop\n\tnop\n\t");}
    if(Jitter3 == 135){asm volatile("nop\n\tnop\n\tnop\n\t");}
    if(Jitter3 == 134){asm volatile("nop\n\t");}
    if(Jitter3 == 133){asm volatile("nop\n\t");}
#endif
if(srxlChData.values[1]==0 ) NOP(); //ServoSetup(); Don't move the servo during no RX signal event at startup
  else 
  {
  TCNT1 = 0;                                         // Restart counter for timer1
  TCNT2 = 0;                                         // Restart counter for timer2
  sei();
  *OutPort1A &= ~OutBit1A;                           // Set pulse low to if not done already
  *OutPort1B &= ~OutBit1B;                           // Set pulse low to if not done already
  OutPort1A = OutPortTable[Timer2Toggle];            // Temp port for COMP1A
  OutBit1A = OutBitTable[Timer2Toggle];              // Temp bitmask for COMP1A
  OutPort1B = OutPortTable[Timer2Toggle+10];         // Temp port for COMP1B
  OutBit1B = OutBitTable[Timer2Toggle+10];           // Temp bitmask for COMP1B

  OCR1A = ServoPW[Timer2Toggle]-8020;
  OCR1B = ServoPW[Timer2Toggle+10]-8015; 
  Timer2Toggle++;                                    // Next servo in line.
  if(Timer2Toggle==10)
  { 
    Timer2Toggle = 0;                                // If next servo is greater than 9, start on 0 again.
                                   
  }
  OutPortNext1A = OutPortTable[Timer2Toggle];        // Next Temp port for COMP1A
  OutBitNext1A = OutBitTable[Timer2Toggle];          // Next Temp bitmask for COMP1A
  OutPortNext1B = OutPortTable[Timer2Toggle+10];     // Next Temp port for COMP1B
  OutBitNext1B = OutBitTable[Timer2Toggle+10];       // Next Temp bitmask for COMP1B
  }
}

void ServoSetup()
{
  // Timer 1 setup(16 bit):
  TCCR1A = 0;                     // Normal counting mode 
  TCCR1B = 2;                     // Set prescaler to 1 
  TCNT1 = 0;                      // Clear timer count 
  TIFR1 = 255;                    // Clear  pending interrupts
  TIMSK1 = 6;                     // Enable the output compare A and B interrupt 
  // Timer 2 setup(8 bit):
  TCCR2A = 0;                     // Normal counting mode 
  TCCR2B = 6;                     // Set prescaler to 256
  TCNT2 = 0;                      // Clear timer count 
  TIFR2 = 255;                    // Clear pending interrupts
  TIMSK2 = 6;                     // Enable the output compare A and B interrupt 
  OCR2A = 106;                     // 93 Set counter A for about 500us before counter B below; 106 for 220us
  OCR2B = 137;                    // Set counter B for about 2000us (137 is 22ms, 124 20ms/10, where 20ms is 50Hz);

  timersRunning = true;
}

void initServoOutputs()
{
  for(iCount=2;iCount< NO_OF_OUTPUT_CHANNELS+2;iCount++) pinMode(iCount, OUTPUT);    // Set all pins used to output:
}

void NOP()// Dummy function Don't move the servo during startup or without SRXL2 Signal
  {
  if (validServoPacket && (!timersRunning)) ServoSetup();// The 328P need this, the 328PB need that not. Odd
  }
  
//Failsafe for the channels for the PWM channels. Don't change this or you override the RX failsafe! Use the forward programming for the PWM channels!
void defaultServoValues()
{
  for (int i=c; i < NO_OF_INPUT_CHANNELS; i++)//
  {
    
    {
     ServoPW[i] = DSMX_2K_CENTER + DSMX_2K_OFFSET;
    }
     
  }
}

///////////////////////// SRXL2 channel interface //////////////////////////////

void userProvidedReceivedChannelData(SrxlChannelData* pChannelData, bool isFailsafe)
{
  int noOfChvalues = 0;

      // Get channel values.
    for (int i=0; i < NO_OF_INPUT_CHANNELS; i++) // Don't change this function or the X-Plus channel range is halved
    {
      ServoPW[i] = srxlChData.values[inputChannelMap[i]] >> 5;    // 16-bit to 11-bit range (0 - 2048)
                  
      {
        noOfChvalues++; // Count valid data
      }
      ServoPW[i] += DSMX_2K_OFFSET;

      // Did we get any valid data ??
      if (noOfChvalues > 0) validServoPacket = true; 
      
    }
    
    wdt_reset();/* Watchdog zurücksetzen. Reset the Watchdog. Belongs in this place for save wdt working and for a save SRXL2 signal loss handling.
    It's now save for use to use for elctro and Turbine ECUs with signal loss failsafe. Need aditional work for internal combustion engines in fact it's
    unsave. No PWM signal on the Expander PWM outputs  
    */
    if (isFailsafe) // Belongs in this place or PWM RX failsafe don't work 
  {
    defaultServoValues();
  }
  }

  void uartSetBaud(uint8_t uart, uint32_t baudRate) // Automatic adjust SRXL2 baudrate.
  {
    // Not supported yet
  }

  void uartTransmit(uint8_t uart, uint8_t* pBuffer, uint8_t length)
  {
    for (uint8_t i=0; i < length; i++)
    {
      srxl2port.write(pBuffer[i]);
    }
  }

[joepasquariello]

PORTD is an instance of class PORTDemulation, and your code attempts to cast the address of PORTD to a uint8_t*. The compiler is saying no, you cannot do that.

[xdog12]

PORTD is an instance of class PORTDemulation, and your code attempts to cast the address of PORTD to a uint8_t*. The compiler is saying no, you cannot do that.

Thank you, I don't know what that means and I don't know how to get this Arduino code to work with teensy. Can you explain what I should do to fix the code?

[joepasquariello]

Thank you, I don't know what that means and I don't know how to get this Arduino code to work with teensy. Can you explain what I should do to fix the code?

I don't know much about AVR, but it looks like Teensy provides emulation of AVR i/o ports. You are not going to be able to write to PORTD, PORTB, etc. via uint8_t variables. You can probably do things like:

PORTD = value;

but not

uint8_t *ptr = PORTD;
*ptr = value;

So, it looks like that code is really AVR specific, and it's going to require major changes to port it to Teensy. Maybe somebody else has a better answer for you. I can't be any more specific, but I don't know anything about one-wire or your specific device. You can see this in the header of your file:

SRXL2 decoder example for Base Receivers and ATMega328P