File content as of revision 1:450090bdb6f4:

#include "mbed.h"
#include "Alternator.h"


/*
    Alternator Regulator
    Jon Freeman
    June 2019 - Feb 2020
    
    ** Prototype built using Nucleo L432KC. Final design likely to use F401RE. Code should compile for either. **
    
    **  main loop frequency upped from 32Hz to 100Hz **

    WHAT THIS PROGRAMME DOES - Controls 4 stroke petrol engine driving vehicle alternator with new custom regulator
    
    Electronics powered by higher voltage of small 12v backup battery, or alternator field output supply
        Note only Field+ and MAX5035 supplied thus, all else powered from MAX outputs.
    Starting engine provides rectified tickle from magneto to enable MAX5035 creating +5 and +3v3 supplies.
    Alternative, selected by jumper pposition, is external switch - battery+ to MAX enable circuit.
    Anytime engine revs measured < 2000 (or some such) RPM, field current OFF (by pwm 0)
    
    BEGIN
        Loop forever at 100 Hz   {
            Read engine RPM by monitoring engine tacho signal present on engine On/Off switch line
            Read alternator output load current
            Using RPM and current readings, regulate engine rpm via model control servo
            Adjust Alternator field current max limit according to RPM (analogue regulator limits output voltage)
            Measure system voltage (just in case this is ever useful)
            Respond to any commands arriving at serial port (setup and test link to laptop)
            Flash LED at 8 Hz as proof of life
        }
    END

    INPUTS  AnalogIn x 2 - Ammeter chip - current and offset AnalogIns
    INPUT   AnalogIn - System voltage for info only.
    INPUT   AnalogIn - ExtRevDemand
    INPUT   AnalogIn - DriverPot
    INPUT   Pulse engine speed indicator, speed checked against EEPROM data to select max pwm duty ratio for this speed
    INPUT   Final pwm gate drive wired back to InterruptIn ** MAYBE USEFUL OR NOT ** Could read this back via serial to laptop
    OUTPUT  pwm to MCP1630. This is clock to pwm chip. Also limits max duty ratio
    RS232 serial via USB to setup eeprom data
*/
//  Uses software bit banged I2C - DONE (because no attempt to get I2C working on these small boards has ever worked)

/**
*   Jumpers fitted to small mbed Nucleo boards - D5 - A5 and D4 - A4 CHECK - yes
*/
//#ifdef  TARGET_NUCLEO_F303K8    //  Code too large to fit
#ifdef  TARGET_NUCLEO_L432KC    //
/*
    declared in file i2c_bit_banged.cpp
DigitalInOut    SDA (D4);       //  Horrible bodge to get i2c working using bit banging.
DigitalInOut    SCL (D5);       //  DigitalInOut do not work as you might expect. Fine if used only as OpenDrain opuputs though!
DigitalIn       SDA_IN  (A4);   //  That means paralleling up with two other pins as inputs
DigitalIn       SCL_IN  (A5);   //  This works but is a pain. Inbuilt I2C should have worked but never does on small boards with 32 pin cpu.
*/
Serial  pc      (USBTX, USBRX); //  Comms port to pc or terminal using USB lead
BufferedSerial  LocalCom    (PA_9, PA_10);  //  New March 2019
//  Above combo of Serial and BufferedSerial is the only one to work !

//  INPUTS :
AnalogIn    Ain_SystemVolts (A6);   //  Sniff of alternator output, not used in control loop as done using analogue MCP1630
AnalogIn    Ammeter_In      (A1);   //  Output of ASC709LLFTR ammeter chip (pin 20), used to increase engine revs if need be
AnalogIn    Ammeter_Ref     (A0);   //  Ref output from ASC709LLFTR used to set ammeter zero (pin 25)

//  Nov 2019. Not convinced Ext_Rev_Demand is useful
AnalogIn    Ext_Rev_Demand  (D3);   //  Servo determines engine revs, servo out to be higher of Ext_Rev_Demand and internal calc

AnalogIn    Driver_Pot      (A3);   //  If whole control system can be made to fit

/*
    MODULE PIN USAGE    
1   PA_9 D1     LocalCom Tx
2   PA_10 D0    LocalCom Rx
3   NRST        
4   GND     
5   PA12_D2     NEW June 2019 - Output engine tacho cleaned-up, brought out to testpoint 4
6   PB_0 D3     AnalogIn Ext_Rev_Demand
7   PB_7 D4     SDA i2c to 24LC memory
8   PB_6 D5     SCL i2c to 24LC memory
9   PB_12 D6    PwmOut     PWM_OSC_IN Timebase for pwm, also determines max duty ratio
10  N.C.        
11  N.C.        
12  PA_8 D9     InterruptIn pulse_tacho from engine magneto, used to measure rpm
13  PA_11 D10   Throttle servo
14  PB_5 D11   //  InterruptIn VEXT PWM controller output folded back for cpu to monitor, useful on test to read what pwm required to do what
15  PB_4 D12    Scope_probe
16  PB_3 D13 LED    Onboard LED
17  3V3         
18  AREF        
19  PA_0 A0     AnalogIn Ammeter_Ref
20  PA_1 A1     AnalogIn Ammeter_In
21  PA_3 A2     PWM analogue out
22  PA_4 A3     AnalogIn Driver_Pot
23  PA_5 A4     n.c. SDA_IN paralleled to i2c pin, necessary because i2c has to be bit banged
24  PA_6 A5     n.c. SCL_IN paralleled to i2c pin, necessary because i2c has to be bit banged
25  PA_7 A6     AnalogIn V_Sample system link voltage
26  PA_2 A7     Not used
27  5V          
28  NRST        
29  GND         
30  VIN         
*/

InterruptIn pulse_tacho     (D9);  //  Signal from engine magneto (clipped by I limit resistor and 3v3 zener)
InterruptIn VEXT            (D2);     //  PWM controller output folded back for cpu to monitor, useful on test to read what pwm required to do what
//  OUTPUTS :

DigitalOut  Scope_probe     (D12);   //  Handy pin to hang scope probe onto while developing code
DigitalOut  myled           (LED1);        //  Green LED on board is PB_3 D13
PwmOut      PWM_OSC_IN      (A2);   //  Can alter prescaler can not use A5
//PwmOut      A_OUT           (A2);   //  Can alter prescaler can not use A5    PIN STOLEN BY PWM_OSC_IN
Servo       Throttle        (D10);   //  Changed from A2, June 2019
DigitalOut  EngineTachoOut  (D11);   //  New June 2019
#endif

#ifdef  TARGET_NUCLEO_F401RE    //
//Serial  pc      (USBTX, USBRX); //  Comms port to pc or terminal using USB lead
BufferedSerial  pc          (PA_2, PA_3, 2048, 4, NULL);    //  Pins 16, 17    tx, rx to pc via usb lead
//BufferedSerial  pc          (USBTX, USBRX);    //  Pins 16, 17    tx, rx to pc via usb lead
BufferedSerial  LocalCom    (PC_6, PC_7);    //  Pins 37, 38  tx, rx to Touch Screen Controller

//  INPUTS :
AnalogIn    Ain_SystemVolts (PB_1);   //  Sniff of alternator output, not used in control loop as done using analogue MCP1630
AnalogIn    Ammeter_In      (PC_5);   //  Output of ASC709LLFTR ammeter chip (pin 20), used to increase engine revs if need be
AnalogIn    Ammeter_Ref     (PB_0);   //  Ref output from ASC709LLFTR used to set ammeter zero (pin 25)
AnalogIn    Ext_Rev_Demand  (PC_1);   //  Servo determines engine revs, servo out to be higher of Ext_Rev_Demand and internal calc
AnalogIn    Driver_Pot      (PC_2);   //  If whole control system can be made to fit

/*
    MODULE PIN USAGE    
*/

InterruptIn pulse_tacho     (PB_15);  //  Signal from engine magneto (clipped by I limit resistor and 3v3 zener)
InterruptIn VEXT            (PC_12);     //  PWM controller output folded back for cpu to monitor, useful on test to read what pwm required to do what
//  OUTPUTS :

DigitalOut  Scope_probe     (PB_3);   //  Handy pin to hang scope probe onto while developing code
DigitalOut  myled           (PA_5);        //  Green LED on board is PA_5
//PwmOut      PWM_OSC_IN      (PA_10);   //  PA_10 is pwm1/3 Can alter prescaler can not use A5
PwmOut      PWM_OSC_IN      (PB_9);   //  PA_10 is pwm4/4 Can alter prescaler can not use A5
PwmOut      A_OUT           (PB_5);   //  PB_5 is pwm3/2 Can alter prescaler can not use A5    PIN STOLEN BY PWM_OSC_IN
Servo       Throttle        (PA_0);   //  PA_8 is pwm1/1 Changed from A2, June 2019
DigitalOut  EngineTachoOut  (PA_7);   //  New June 2019

I2C i2c                     (PB_7, PB_6);   //  Pins 58, 59 For 24LC64 eeprom
//#define SDA_PIN PB_7
//#define SCL_PIN PB_6

#endif

Timer   microsecs;
Ticker  loop_timer;     //  Device to cause periodic interrupts, used to sync iterations of main programme loop - slow

const   double  AMPS_CAL = 90.0;
extern  eeprom_settings user_settings  ;
//  SYSTEM CONSTANTS
/*  Please Do Not Alter these */
const   int     MAIN_LOOP_REPEAT_TIME_US    = 10000;    //  10000 us, with TACHO_TAB_SIZE = 100 means tacho_ticks_per_time is tacho_ticks_per_second
/*  End of Please Do Not Alter these */
/*  Global variable declarations */
uint32_t    //semaphore           = 0,
            speed_control_factor= 75000,  //  fiddled from cli to tweak engine speed controller response
            volt_reading        = 0,    //  Global updated by interrupt driven read of Battery Volts
            ext_rev_req         = 0,
            driver_reading      = 0,
            tacho_count         = 0,    //  Global incremented on each transition of InterruptIn pulse_tacho
            sys_timer100Hz      = 0;    //  gets incremented by our Ticker ISR every MAIN_LOOP_REPEAT_TIME_US
double      amp_reading         = 0.0,
            amp_offset          = 0.0,
            raw_amp_reading     = 0.0,
            raw_amp_offset      = 0.0;
double      servo_position = 0.2;   //  set in speed control loop
//    const double    throttle_limit = 0.4;
double      throttle_limit = SERVO_MAX;
bool        loop_flag   = false;    //  made true in ISR_loop_timer, picked up and made false again in main programme loop
bool        flag_25Hz   = false;    //  As loop_flag but repeats 25 times per sec
bool        flag_12Hz5  = false;    //  As loop_flag but repeats 12.5 times per sec
bool        flag_1Hz    = false;    //  As loop_flag but repeats 1 times per sec
bool        query_toggle    = false;

const int AMP_FILTER_FACTOR    = 6;

/*  End of Global variable declarations */

//void    ISR_fast_interrupt  ()  {   //  here at 10 times main loop repeat rate (i.e. 1000Hz, 1.0ms)
void    ISR_fast_interrupt  ()  {
    static  uint32_t t = 0;
    Scope_probe = 1;    //  To show how much time spent in interrupt handler
    switch  (t) {
        case    0:
            volt_reading    >>= 1;                                 //  Result = Result / 2
            volt_reading    += Ain_SystemVolts.read_u16    ();     //  Result = Result + New Reading
            break;
        case    1:
            raw_amp_reading = (double) Ammeter_In.read();
            break;
        case    2:
            raw_amp_offset = Ammeter_Ref.read();    //  Feb 2020 Not convinced this is useful
            break;
        case    3:
            ext_rev_req     >>= 1;                                 //  Result = Result / 2
            ext_rev_req     += Ext_Rev_Demand.read_u16();
            break;
        case    4:
            driver_reading  >>= 1;                                 //  Result = Result / 2
            driver_reading  += Driver_Pot.read_u16();
//            break;
//        case    5:
            loop_flag = true;   //  set flag to allow main programme loop to proceed
            sys_timer100Hz++;        //  Just a handy measure of elapsed time for anything to use
            if  ((sys_timer100Hz & 0x03) == 0)  //  is now 12.5Hz, not 8
                flag_25Hz  = true; //  flag gets set 25 times per sec. Other code may clear flag and make use of this
        default:
            break;
    }
    t++;
    if  (t > 9)
        t = 0;
    Scope_probe = 0;    //  To show how much time spent in interrupt handler
}



//  New stuff November 2019
/**
*   Obtaining Amps_Deliverable from RPM.
*   Lucas workshop sheet shows exponential relationship between RPM over threshold, and Amps_Deliverable,
*   That is Amps_Deliverable rises steeply with RPM, flattening off towards 6000 RPM
*   Curve modeled by eqn
*       I_del = I_max (1 - exp(-(RPM-3000)/Const1))       where Const1 = 1000 is a starting point
*   This is probably fine when driving alternator with BIG engine.
*   When using small engine, rising load current sags engine RPM.
*   Using a linear relationship builds in a good safety margin, possible eqn
*       I_del = I_max (RPM - 3000) / 3000     for use over RPM range 3000-6000
*/
const   double  RPM_Threshold   = 3000.0;
const   double  RPM_Max         = 6000.0;
//const   double  I_max = 30.0;
const   double  RPM_Range   = RPM_Max - RPM_Threshold;
//#define BIG_ENGINE

double  Calculate_Amps_Deliverable (uint32_t RPM)  {
    double r = (double)RPM - RPM_Threshold;
    r /= RPM_Range;
    if  (r < 0.0)
        r = 0.0;
    if  (r > 1.0)
        r = 1.0;
#ifdef  BIG_ENGINE
    const   double  Const1 = -3.2;    //  Tweak this to adjust shape of exponential function
    return  (1.0 - exp(r*Const1));
#else
    return  r;
#endif
}

class   one_over_s_integrator   {   //  Need this to drive servo  Jan 2020 why?
    double  internal_integral, max, min, Hz, gain;
    public:
    one_over_s_integrator   ()  {   internal_integral = 0.0; max = 1.0; min = -1.0; Hz = 100.0; gain = 1.0;}
    double  integral    (double input)  ;
    void    set_max (double)    ;
    void    set_min (double)    ;
    void    set_gain (double)    ;
    void    set_sample_time (double)    ;
}   ;

void    one_over_s_integrator::set_max (double in)  {
    max = in;
}
void    one_over_s_integrator::set_min (double in)  {
    min = in;
}
void    one_over_s_integrator::set_gain (double in)  {
    gain = in;
}
void    one_over_s_integrator::set_sample_time (double in)  {
    Hz = 1.0 / in;
}
double  one_over_s_integrator::integral (double input)  {
    internal_integral += gain * input / Hz;     //  100 for 100Hz update rate
    if  (internal_integral > max)
        internal_integral = max;
    if  (internal_integral < min)
        internal_integral = min;
    return  internal_integral;
}

//double  one_over_s  ()
//  End of New stuff November 2019


//  New stuff June 2019
bool    magneto_stretch = false;
Timeout magneto_timo;
uint32_t magneto_times[8] = {0,0,0,0,0,0,0,0};  //  June 2019, only 2 of these used


/**    
    void    magneto_timeout ()
    Here 5ms after magneto pulse detected
    This is sufficient time for ringing to cease, not long enough to lose next pulse even at max engine revs.
    Reset 'magneto_stretch' flag set and used in 'ISR_magneto_tacho'
*/
void    magneto_timeout ()
{
    magneto_stretch = false;    //  Magneto ringing finished by now, re-enable magneto pulse count
    EngineTachoOut  = 0;    //  Cleaned tacho output brought out to pin to look at with scope
}

/**
void    ISR_magneto_tacho   ()  ;   //  New June 2019
    //      Engine On/Off switch turns engine off by shorting ignition volts magneto to ground.
    //      Therefore when engine running, have pulse signal one pulse per rev (even though 4 stroke, spark delivered at 2 stroke rate)
    //      Pulse spacing 20ms @ 3000 RPM, 60ms @ 1000 RPM, 6ms @ 10000 RPM
    
            Magneto signal rings, is quite unclean, therefore a cleanup strategy is needed.
            Solution - On arrival at this interrupt handler,
                If flag 'magneto_stretch' true, do nothing and return (to avoid multiple pulse count)
                Set flag 'magneto_stretch' true;
                Start timer 'magneto_timo' to cause 'magneto_timeout' interrupt in a time longer than ringing bt shorter than shortest time to next spark
                Record time between most recent two sparks and set output bit for scope monitoring
*/
void    ISR_magneto_tacho   ()  //  This interrupt initiated by rising (or falling) edge of magneto output, (not both)
{
    if  (!magneto_stretch)
    {
        uint32_t    new_time = microsecs.read_us();
        if  (new_time < magneto_times[1])      //  rollover detection
            magneto_times[1] = 0;
        magneto_times[0] = new_time - magneto_times[1];    //  microsecs between most recent two sparks
        magneto_times[1] = new_time;    //  actual time microsecs of most recent spark
        magneto_stretch = true;
        magneto_timo.attach_us (&magneto_timeout, 5000);    //  To ignore ringing and multiple counts on magneto output, all settled within about 5ms
        tacho_count++;
        EngineTachoOut  = 1;    //  Cleaned tacho output brought out to pin to look at with scope
    }
}

//  Endof New stuff June 2019

const   double  shrink = 0.2;
/*double  lpf_4th_order_asym    (double input)  {
*
*   input is driver's control pot.
*   This needs regular calling, maybe 8Hz - 32Hz
*
*   Output from 4th stage of cascaded Butterworth lpf section
*   Used to delay rising input to motor controller allowing time for engine revs to rise
*/
double  lpf_4th_order_asym    (double input)  {
    static  double  lpfs[] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0};
    if  (input < 0.0)   input = 0.0;
    if  (input > 1.0)   input = 1.0;
    lpfs[0] = input;    //  zeroth order filter
    double tmp;
    for (int order = 1; order < 5; order++) {
        tmp = (lpfs[order] * (1.0 - shrink))
              + (lpfs[order - 1] * shrink);
        if  (tmp > input)
            tmp = input;
        lpfs[order] = tmp;
    }
    return  tmp;
}


    VEXT_Data   Field;


void    ISR_VEXT_rise    ()  //  InterruptIn interrupt service
{   //  Here is possible to read back how regulator has controlled pwm - may or may not be useful
    uint32_t    tmp = microsecs.read_us();
    Field.measured_period = tmp - Field.t_on;
    Field.t_on = tmp;
    Field.rise_count++;
}
void    ISR_VEXT_fall    ()  //  InterruptIn interrupt service
{
    Field.fall_count++;
    Field.t_off = microsecs.read_us();
    Field.measured_pw_us = Field.t_off - Field.t_on;
}
//  ****    End of Interrupt Service Routines   ****


/** uint32_t    ReadEngineRPM  ()
*   
*   June 2019 - Replaced count of alternator frequency by count of engine magneto pulses.
*   
*/
uint32_t    ReadEngineRPM  ()
{
    uint32_t time_since_last_spark = microsecs.read_us() - magneto_times[1];
    if  (time_since_last_spark > 250000)     //  if engine probably stopped, return old method RPM
        return  0;
    return  (60000000 / magneto_times[0]);  //  60 million / microsecs between two most recent sparks, eg 10,000us between sparks @ 6000 RPM
}

/*double  Read_Ext_Rev_Req    ()
{
    double  rv = (double) ext_rev_req;
    return  rv / 4096.0;
}*/

double  Read_Driver_Pot    ()
{
    double  rv = (double) driver_reading;
    return  rv / 4096.0;
}

double  Read_AlternatorAmps   ()
{
    int32_t diff    = amp_reading - amp_offset;
    double  amps    = ((double) diff) / (1 << AMP_FILTER_FACTOR);
    amps -= 365.0;  //  offset probably specific to particular board.
    amps /= 1433.0;     //  fiddle factor
    return  amps;
}

double  Read_BatteryVolts   ()
{
    return  ((double) volt_reading) / 3282.5;    //  divisor fiddled to make voltage reading correct !
}

void    Read_Ammeter   (double * p)  
{
    p[0] = amp_reading;
    p[1] = amp_offset;
}

/**
void    set_servo   (double p)  {   //  Only for test, called from cli
*/
void    set_servo   (double p)  {   //  Only for test, called from cli
    Throttle = p;
}

double  normalise   (double * p)   {
    if  (*p > 0.999)
        *p = 0.999;
    if  (*p < 0.001)
        *p = 0.001;
    return  * p;
}

uint32_t    RPM_demand = 0;         //  For test, set from cli 'sv'
/**
*/
void    set_RPM_demand  (uint32_t   d)  {
    if  (d < 10)
        d = 10;
    if  (d > MAX_RPM_LIMIT)
        d = MAX_RPM_LIMIT;
    RPM_demand = d;
}

/**void    set_pwm (double d)   {   Range 0.0 to 1.0
    This PWM used to limit max duty ratio of alternator field energisation.
    With R25=33k and C4=100n controlling ramp input to CS pin of MCP1630 (not MCP1630V),
    ramp terminates fet 'on' pulse after a max of approx 980 us.
    With const   int PWM_PERIOD_US = 2000    , duty ratio is thus limited to approx 50% max.
    This is about right when using 12V alternator on 24V systems
    A 1.225V reference (U7) is fed to the MCP1630 error amp which compares this to fed-back proportion of system voltage.
    This adjusts final PWM down to zero % as needed to maintain alternator output voltage.
*/
void    set_pwm (double d)   {
    uint32_t i;
    if  (d < 0.0)
        d = 0.0;
    if  (d > 1.0)
        d = 1.0;
    i = (uint32_t)(d * (PWM_PERIOD_US / 2));   //  div 2 when using 12v alternator in 24v system
//    pc.printf   ("Setting PWM to %d\r\n", i);
    PWM_OSC_IN.pulsewidth_us  (PWM_PERIOD_US - i);            //  Note PWM is inverted as MCP1630 uses inverted OSC_IN signal
}

void    speed_control_factor_set    (struct parameters & a)    {
    uint32_t v = (uint32_t)a.dbl[0];
    if  (v > 10)
        speed_control_factor = v;
    pc.printf   ("speed_control_factor %d\r\n", speed_control_factor);
}

void    set_throttle_limit    (struct parameters & a)    {
    if  (a.dbl[0] > 0.01 && a.dbl[0] < 1.001)
        throttle_limit = a.dbl[0];
    pc.printf   ("throttle_limit %.2f\r\n", throttle_limit);
}

void    query_system    (struct parameters & a)    {
    query_toggle = !query_toggle;
//    pc.printf   ("Stuff about current state of system\r\n");
//    pc.printf   ("RPM=%d, servo%.2f\r\n", ReadEngineRPM  (), servo_position);
}

extern  void    command_line_interpreter    ()  ;   //  Comms with optional pc or device using serial port through board USB socket
extern  bool    i2c_init    ()  ;
extern  int     check_24LC64    ()  ;

//  Programme Entry Point
int main()
{
    //  local variable declarations
//    double      servo_position = 0.2;   //  set in speed control loop
    double      revs_error;
    double      Amps_Deliverable = 0.0;     //  New Nov 2019
//    double      tempfilt = 0.0, servo_fucker = 0.01;
    
    int32_t    RPM_ave = 0, RPM_filt = 0, RPM_tmp;
    int32_t irevs_error;
    uint32_t ticks = 0;
    
    pulse_tacho.fall        (&ISR_magneto_tacho); //    1 pulse per engine rev
    VEXT.rise               (&ISR_VEXT_rise);   //  Handles - MCP1630 has just turned mosfet on
    VEXT.fall               (&ISR_VEXT_fall);   //  Handles - MCP1630 has just turned mosfet off
    microsecs.reset()   ;   //  timer = 0
    microsecs.start ()  ;   //  64 bit, counts micro seconds and times out in half million years

    PWM_OSC_IN.period_us      (PWM_PERIOD_US); //  about 313Hz * 2
//  PROBLEM using same pwm, common prescaler, can't update servo that fast, can't pwm field that slow.

    PWM_OSC_IN.pulsewidth_us  (PWM_PERIOD_US / 2);            //  value is int
//    PWM_OSC_IN.pulsewidth_us  (PWM_PERIOD_US);            //  value is int
#ifdef  TARGET_NUCLEO_F401RE    //
    A_OUT.period_us     (100);  //  pwm as analogue out
    A_OUT.pulsewidth_us (19);
#endif
    Throttle    = servo_position;
    pc.printf   ("\r\n\n\n\n\nAlternator Regulator 2020, Jon Freeman, SystemCoreClock=%d\r\n", SystemCoreClock);
    if  (!i2c_init())
        pc.printf   ("i2c bus failed init\r\n");
    pc.printf   ("check_24LC64 returned 0x%x\r\n", check_24LC64());
    user_settings.load   ()  ;   //  Fetch values from eeprom, also builds table of speed -> pwm lookups
//    pc.printf   ("Loaded\r\n");
    //  Setup Complete ! Can now start main control forever loop.
    loop_timer.attach_us    (&ISR_fast_interrupt, MAIN_LOOP_REPEAT_TIME_US / 10);    //  Start periodic interrupt generator 1000us at Feb 2020

//***** START OF MAIN LOOP
    while   (1) {      //  Loop forever, repeats synchroised by waiting for ticker Interrupt Service Routine to set 'loop_flag' true
        while   (!loop_flag)  {         //  Most of the time is spent in this loop, repeatedly re-checking for commands from pc port
            command_line_interpreter    ()  ;   //  Proceed beyond here once loop_timer ticker ISR has set loop_flag true
        }               //  Jun 2019 pass here 100 times per sec
//  BEGIN 100Hz stuff
        loop_flag = false;              //  Clear flag set by ticker interrupt handler
        
        //  Three variations on engine rpm.
        RPM_tmp = ReadEngineRPM ();
        RPM_ave += RPM_tmp;     //  Rising sum needs dividing and resetting to 0 when used
        RPM_filt += RPM_tmp;
        RPM_filt >>= 1;
        
        amp_reading += (raw_amp_reading - 0.5) * AMPS_CAL;
        amp_reading /= 2.0;
        amp_offset  += (raw_amp_offset - 0.5) * AMPS_CAL;   //  This reading probably not useful
        amp_offset /= 2.0;
        
        Amps_Deliverable = Calculate_Amps_Deliverable   (ReadEngineRPM  ());    //  Added Nov 2019, not yet used. Returns normalised 0.0 to 1.0
        
//        PWM_OSC_IN.pulsewidth_us  (user_settings.get_pwm(ReadEngineRPM()));    //  Update field current limit according to latest measured RPM

//        while   (LocalCom.readable())   {
//            int q = LocalCom.getc();
//            //q++;
//            pc.putc (q);
//        }
//  END 100Hz stuff
        if  (flag_25Hz)  {
            flag_25Hz = false;
//  BEGIN   25Hz stuff

//  END 25Hz stuff
//  BEGIN   12.5Hz stuff
            flag_12Hz5 = !flag_12Hz5;
            if  (flag_12Hz5)  {   //  Do any even stuff to be done 12.5 times per second
#ifdef  SPEED_CONTROL_ENABLE
                if  (RPM_demand < TICKOVER_RPM)
                    servo_position = Throttle = 0.0;
                else    {
                    RPM_ave /= 8;
//                    irevs_error = RPM_demand - ReadEngineRPM  ();
                    irevs_error = RPM_demand - RPM_filt;
                    revs_error = (double) irevs_error;
                    if  (abs(revs_error) > 3.0)    {    //  if speed error > 3rpm, tweak, otherwise deadband
                        //servo_position += (revs_error / 7500.0);
                        servo_position += (revs_error / speed_control_factor);
                        servo_position = normalise(&servo_position);
                        if  (servo_position < 0.0 || servo_position > 1.0)
                            pc.printf   ("servo_position error %f\r\n", servo_position);
                        if  (servo_position > throttle_limit)
                            servo_position = throttle_limit;
                        Throttle = servo_position;
                    }
                }
                RPM_ave = 0;    //  Reset needed
#endif
            }
            else    {               //  Do odd 12.5 times per sec stuff
                flag_12Hz5  = false;
                myled = !myled;
                LocalCom.printf ("%d\r\n", volt_reading);
    //void    set_pwm (double d)   {
                
    //            set_pwm (user_settings.get_pwm(ReadEngineRPM()));
                
    /*            servo_position += servo_fucker;
                if  (servo_position > 1.0 || servo_position < 0.0)
                    servo_fucker *= -1.0;
                Throttle = servo_position;
    */            
            }   //  End of if(flag_12Hz5)
//  END 12.5Hz stuff
            ticks++;    //  advances @ 25Hz
            if  (ticks > 24) {   //  once per sec stuff
//  BEGIN   1Hz stuff
                ticks = 0;
                if  (query_toggle)  {
                    pc.printf   ("V=%.1f\tI=%.1f\tRPM=%d\tservo%.2f\r\n", Read_BatteryVolts(), amp_reading, ReadEngineRPM  (), servo_position);
                }
//                pc.printf   ("Tick %d\r\n", flag_12Hz5);
//                tempfilt *= 0.99;
//                tempfilt += Read_AlternatorAmps() * 0.01;
//                pc.printf   ("RPM %d, err %.1f, s_p %.2f, lut %.3f\r\n", ReadEngineRPM  (), revs_error, servo_position, user_settings.get_pwm(ReadEngineRPM()));
//                pc.printf   ("Vbat %.2f, servo %.3f, amps %.3f, filt %.3f\r\n", Read_BatteryVolts(), servo_position, Read_AlternatorAmps(), tempfilt);
//  END 1Hz stuff
            }   //  eo once per second stuff
        }   //  End of 100Hz stuff
    }       //  End of main programme loop
}           //  End of main function - end of programme
//***** END OF MAIN LOOP