// Chapter 13 6811 C programs// Jonathan W. Valvano// This software accompanies the book,// Embedded Microcomputer Systems: Real Time Interfacing// published by Brooks Cole, 1999// Program 13.1. C implementation of a Traffic Light Controller./* Port B bits 5-0 outputs that control the traffic signal */const struct State {  unsigned char Out;         /* Output to Port B */  unsigned short Time;       /* Time in sec to wait */  const struct State *Next;  /* Next state */};typedef const struct State StateType;#define NorthRed_EastGreen  &fsm[0]#define NorthRed_EastYellow &fsm[1]#define NorthGreen_EastRed  &fsm[2]#define NorthYellow_EastRed &fsm[3]StateType fsm[4]={/* NorthRed_EastGreen, wait= 3 min, next state */  {0x21, 180, NorthRed_EastYellow},  /* NorthRed_EastYellow, wait= 15 sec, next state */  {0x22, 15, NorthGreen_EastRed},  /* NorthGreen_EastRed, wait= 3 min, next state */  {0x0C, 180, NorthYellow_EastRed},   /* NorthYellow_EastRed, wait= 15 sec, next state */  {0x14, 15, NorthRed_EastGreen}};void main(void){ StatePtr *Pt;  /* Current State */  Pt=NorthRed_EastGreen; /* Initial State */  DDRB=0xFF;             /* Make Port B outputs  */  while(1){    PORTB=Pt->Out;    /* Perform output for this state */    Wait(Pt->Time);   /* Time to wait in this state */    Pt=Pt->Next;      /* Move to next state */  }};// Program 13.2 Circular list used to spin a stepper motor./* Port B bits 3-0 outputs that control the stepper motor */const struct State {  unsigned char Out;         /* Output to Port B */  const struct State *Next;  /* Next state */};typedef const struct State StateType;#define S6  &fsm[0]#define S5  &fsm[1]#define S9  &fsm[2]#define S10 &fsm[3]StateType fsm[4]={  {0x06, S5},    {0x05, S9},    {0x09, S10},    {0x0A, S6};StatePtr *Pt;  /* Current State */unsigned short Speed;// Program 13.3 C software to spin a stepper motor at a constant speed.// MC68HC11A8, ICC11 compiler#define OC5  0x08#pragma interrupt_handler TOC5handler()void TOC5handler(void){  PORTB=Pt->Out; // output for this state   Pt=Pt->Next;   // Move to next state   TFLG1=OC5;     // Ack OC5F   TOC5=TOC5+Speed; // Executed every step  }void ritual(void) { asm(" sei");    // make atomic   TMSK1|=OC5;  // Arm output compare 5   TFLG1=OC5;   // Initially clear OC5F   Speed=10000; // initial speed   Pt=S6;         // initial state  TOC5=TCNT+2000; // First one in 1 msasm(" cli"); }// Program 13.4 Port B is used to turn on the heater.unsigned char Tlow,Thigh,T; int E;  // units in degrees C void Actuator(unsigned char relay){  PORTB=relay;    // turns power on/off}// Program 13.5 Bang-bang temperature control software.// MC68HC11A8, ICC11 compiler#pragma interrupt_handler TOC5handler()void TO5handler(void){   T=SE(A2D(channel)); // estimated T    E=Tstar-T;          // error   if(T<Tlow)      Actuator(0);   // too cold so off   else if (T>Thigh)     Actuator(1);   // too hot so on// leave as is if Tlow<T<Thigh   TOC5=TOC5+rate;  // periodic rate   TFLG1=0x08; }    // ack OC5F// Program 13.6 Incremental position control software.// MC68HC11A8, ICC11 compilerunsigned char Xstar,X; int E;   // in mm#pragma interrupt_handler TOC5handler()void TO5handler(void){ int new;   X=SE(A2D(channel));  // estimated (mm)   E=Xstar-X;     // error (mm)   new=PORTB;     // promote to 16 bits   if(E< -1)     new--; // decrease   else if (E>1) new++; // increase// leave as is if -1<E<1   if(new<0)   new=0;    // underflow   if(new>255) new=255;  // overflow   PORTB=new;   // output to actuator   TOC5=TOC5+rate; // establish periodic   TFLG1=0x08; }       // ack OC5F// Program 13.7 Integral position control software.// MC68HC11A8, ICC11 compilerunsigned int Time;  // Time in msecunsigned int X;     // Est position in cmunsigned int Xstar; // Desired pos in cm unsigned int U;     // Actuator duty cycleunsigned int Cnt;   // once a secunsigned int Told;  // used to meas period#pragma interrupt_handler TOC5handler()void TOC5Handler(void){ int NewU;  TFLG1=0x08;     // Ack OC5F   TOC5=TOC5+2000; // every 1 ms   Time++;     // used to measure period  if((Cnt++)==1000){  // every 1 sec      Cnt=0;// 0<X<100, 0<Xstar<100, 100<U<19900, so// Minimum occurs when U=100,Xstar=0,X=100//    Minimum NewU = -900// Max occurs when U=19900,Xstar=100,X=0//    Maximum NewU = 20900// so NewU will be a valid signed int      NewU=U+10*(Xstar-X);     if(NewU<100) NewU=100;  // Constrain     if(NewU>19900) NewU=19900;     U=NewU;  } }// Program 13.8 PWM actuator control software.// MC68HC11A8, ICC11 compiler#pragma interrupt_handler TOC4handler()void TOC4Handler(void){    TFLG1=OC4F; /* Ack */    if (TCTL1&0x04)   /* OL4 bit *//* OL4=1, High for the next U cycles */       TOC4=TOC4+U;     else/* OL4=0, Low for the next 20000-U cyc */       TOC4=TOC4+20000-U;       TCTL1^=0x04; }     /* Toggle OL4 */ // Program 13.9 Sensor measurement software.// MC68HC11A8, ICC11 compiler// Time is incremented every 1 ms, by OC5// This handler is executed on rise#pragma interrupt_handler TIC1handler()void TIC1Handler(void){unsigned int p;  TFLG1 = IC1F;  // Ack IC1F  p = Time-Told; // period in msec  X = p-10;    // estimated position (cm)  Told=Time;}// Program 13.10 Initialization software.// MC68HC11A8, ICC11 compilervoid ritual(void) {   asm(" sei");      /* atomic */  OC1M=0; OC1D=0;       TCTL1=0x08; // Clear OC4   TCTL2=0x10; // capture on rise of IC1   TMSK1=OC5F+OC4F+IC1F; // Arm      U=10000;      // Initial U , half power  Time = 0; Told=0;  Cnt=0;  TFLG1=OC5F+OC4F+IC1F; // clear flags   TOC5=TCNT+2000; // First OC5 in 1 ms   TOC4=TCNT+100;  // First OC4 in 50us   asm(" cli");}Program 13.11. Subtraction with overflow/underflow checking.char Subtract(unsigned char N, unsigned char M){   /* returns N-M */unsigned int N16,M16; int Result16;     N16=N;        /* Promote N,M */     M16=M;     Result16=N16-M16;   /* -255睷esult16