Memorandum. Introduction. Design. Discussion. Contributions. Conclusion

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1 Memorandum To: Dr. Randy Hoover From: Steffen Link Date: April 7, 2017 Subject: Lab 6: State Machine Stoplight Introduction The objective of the lab was to become more familair with a number of embedded programming concepts including timers, external interrupts, and state machines. To demonstrate this, a stoplight with a crosswalk was to be designed and implemented using the RedBoard and C. Design This lab involved using the Redboard GPIO pins, timer interrupt, and external interrupts 0 and 1 to drive a stoplight with a crosswalk. To implement this a state machine with eight states was used (see Appendix B). The first and fifth (where one light has just turned green) state both will not allow for a pedestrian to cause the stoplights to change to cross. If the light is in a state to let you cross, no change in state is issued. If the state is in state one or six (the light has been green for 2+ seconds), pressing one of the crosswalk buttons will cause the light to begin by stopping traffic and then allowing the pedestrian to cross the intersection. The light will either return to the previous state if less than 3 5 of the time allotted to the green light has passed or continue to let the other way go. When the light is in either state two or seven, a light is yellow and pressing the button to cross the street will trigger flashing lights after traffic has been brought to a full stop. When in state three (all red), the state machine will go to state four (flashing yellow / yeild to pedestrian) if an interrupt has been triggered and will either return to that state or not depending on a return flag set in the interrupt, elsewise it will continue to the other state. This was implemented using a packed struct for the state change variable, two external interrupts, a case statement and a timer interrupt. No data structure was used as it was not seen fit, along with previous expression of understanding of linked list (look at UART code in lab 4). Discussion This method used to implement the program works well, although it could be cleaned up to make the code more readable. The timing is not it was used for a simulation where the lights changed circa once every couple of seconds, so it would have no significant impact on accuracy. One of the important details of GCC discovered is that TIM0 OVF vect is a correct interrupt for Atmel Studio, but GCC does not recognize it. Finally this lab was a good chance to learn how to implement interrupts so that they do not need to be debounced. All together, the method of using state machines was shown to be a relativley easy way to implement a stoplight. Contributions Wrote Libraries Steffen Link Captures from lab Steffen Link State Machine Steffen Link Report - Design & Discussion Steffen Link - Introduction & Conclusion Steffen Link - Formatting & L A TEX Steffen Link Conclusion This lab helped demonstrate uses for interrupts related to timer and external interrupts, as well as how a well designed state machine can be simply implemented to make a simple process. 1

2 Appendices Appendix A Schematics Figure 1: Schematic for Stoplight circuit Appendix B State Machine Figure 2: State machine design for stoplight Table 1: State Transition Table for Stoplight State \ Inputs X000 X001 X010 X X Table 2: Where the inputs are Return N/S, timeout, interrupt 1, intterupt0 respectively 2

3 Appendix C Code C.1 main.c - Main Program 1 / // 2 F i l e : main. c 3 Author : S t e f f e n Link 4 Date : 2017/4/3 5 Lab : 5 6 D e s c r i p t i o n : Main f i l e running the program 7 / 8 // Define CPU freqeuncy 9 #d e f i n e F CPU UL // Inlcude block f o r data 12 #i n c l u d e <avr / i o. h> 13 #i n c l u d e <avr / i n t e r r u p t. h> 14 #i n c l u d e <u t i l / delay. h> 15 #i n c l u d e <s t d i o. h> 16 #i n c l u d e <s t d l i b. h> #d e f i n e rtime 1 / // 1 second f o r i n t e r s e c t i o n c l e a r 19 #d e f i n e ytime 2 / // 2 seconds 20 #d e f i n e gtime 3 / // 3 seconds // Struct f o r s e t t i n g the next s t a t e 23 typedef s t r u c t s t a t e 24 { 25 u i n t 8 t rets : 3 ; 26 u i n t 8 t i n t e r : 2 ; 27 u i n t 8 t nxts : 3 ; 28 u i n t 8 t l t S : 3 ; 29 } s t t e ; // A bunch o f g l o b a l v a r i a b l e s Yo 32 v o l a t i l e f l o a t seconds = gtime ; 33 v o l a t i l e f l o a t count = 0 ; 34 v o l a t i l e f l o a t oldcount = 0 ; 35 v o l a t i l e u i n t 8 t s t a t e = 0 ; 36 // Bit packed u i n t 8 t 37 // 0 b x x x x x x x x 38 // 0 b r s 2 r s 1 r s 0 i n t 0 i n t 1 s2 s1 s0 39 v o l a t i l e s t t e statechange = { 0, 0, 0, 0 } ; / 43 This f u n c t i o n i n i t i a l i z e d the i n t e r r u p t s and PORTD 44 / 45 void i n i t ( void ) 46 { 47 s e i ( ) ; 48 DDRD = 0 b ; 49 TCCR0B = 0x05 ; // Set timer1 p r e s c a l e to f o s c / TIMSK0 = 0x01 ; // Set i n t e r r u p t f o r overflow on Timer0 51 EIMSK = 0x03 ; 52 EICRA = 0x0F ; 53 PCMSK0 = 0x0C ; 54 3

4 55 } / 59 This f u n c t i o n i s the main f u n c t i o n f o r the program to be f l a s h e d 60 / 61 i n t main ( void ) 62 { 63 i n i t ( ) ; // While loop with s t a t e machine i n s i d e with corresponding s t a t e s 66 while ( 1 ) 67 { 68 switch ( s t a t e & 0x07 ) 69 { 70 case 0 : 71 PORTD = 0 b ; 72 seconds = rtime 2 ; 73 statechange. nxts = 1 ; 74 statechange. l t S = 3 ; 75 break ; 76 case 1 : 77 PORTD = 0 b ; 78 count = oldcount ; 79 oldcount = 0 ; 80 seconds = gtime ; 81 statechange. nxts = 2 ; 82 statechange. l t S = 0 ; 83 break ; 84 case 2 : 85 PORTD = 0 b ; 86 seconds = ytime ; 87 statechange. nxts = 3 ; 88 statechange. l t S = 1 ; 89 break ; 90 case 3 : // handles crosswalk and proper r e t u r n i n g 91 PORTD = 0 b ; 92 seconds = rtime ; 93 i f ( ( statechange. i n t e r )!= 0) // checking f o r i n t e r r u p t s 94 { 95 i f ( statechange. l t S!= 3) 96 statechange. nxts = 4 ; 97 e l s e 98 { // c l e a r s i n t e r r u p t s 99 statechange. i n t e r = 0 ; 100 statechange. nxts = statechange. rets ; 101 } 102 } e l s e // r e t u r n s to proper p l a c e 103 { 104 i f ( statechange. l t S == 1) 105 statechange. nxts = 5 ; 106 e l s e 107 statechange. nxts = 0 ; 108 } 109 break ; 110 case 5 : 4

5 111 PORTD = 0 b ; 112 seconds = rtime 2 ; 113 statechange. nxts = 6 ; 114 statechange. l t S = 3 ; 115 break ; 116 case 6 : 117 count = oldcount ; 118 oldcount = 0 ; 119 PORTD = 0 b ; 120 seconds = gtime ; 121 statechange. nxts = 7 ; 122 statechange. l t S = 5 ; 123 break ; 124 case 7 : 125 PORTD = 0 b ; 126 seconds = ytime ; 127 statechange. nxts = 3 ; 128 statechange. l t S = 6 ; 129 break ; 130 case 4 : 131 PORTD = 0 b ; 132 seconds = 0 ; 133 c l i ( ) ; 134 f o r ( i n t i = 0 ; i < 1 0 ; i ++) // Hard coded f l a s h i n g l i g h t s 135 { 136 delay ms (500) ; 137 PORTD ˆ= 0 b ; 138 } 139 s e i ( ) ; 140 seconds = 0 ; 141 PORTD = 0 b ; 142 seconds = rtime ; 143 statechange. nxts = 3 ; 144 statechange. l t S = 3 ; 145 break ; 146 d e f a u l t : 147 PORTD = 0xF9 ; 148 } 149 TCNT0 = 0 ; 150 while ( count < seconds ) ; 151 count = 0 ; 152 s t a t e = statechange. nxts ; 153 } 154 return 1 ; 155 } / 159 This f u n c t i o n increments count everytime TIMER0 r o l e s over ( every 61ms) 160 / 161 ISR ( TIMER0 OVF vect ) 162 { 163 count++; 164 } / 5

6 167 Handles one d i r e c t i o n o f i n t e r r u p t s 168 / 169 ISR ( INT0 vect ) 170 { 171 i f ( s t a t e < 8 && s t a t e > 5) // Checks i f i t s in a worth while s t a t e to do t h i n g s 172 { 173 i f ( s t a t e == 6 && count < 0. 6 ( gtime+rtime 2) ) 174 { 175 statechange. rets = 6 ; 176 statechange. nxts = 7 ; 177 statechange. i n t e r = 1 ; 178 oldcount = count ; 179 } e l s e 180 { 181 statechange. rets = 0 ; 182 statechange. nxts = statechange. l t S == 6? 3 : 6 ; 183 statechange. i n t e r = 1 ; 184 oldcount = 0 ; 185 } 186 i f ( s t a t e == 6) seconds = 0 ; 187 } e l s e i f ( s t a t e == 3) // a l l red s t a t e 188 { 189 statechange. rets = statechange. l t S == 1? 5 : 0 ; 190 statechange. nxts = 4 ; 191 statechange. i n t e r = 1 ; 192 } 193 } / 196 This f u n c t i o n handles the other d i r e c t i o n o f i n t e r r u p t 197 / 198 ISR ( INT1 vect ) 199 { 200 i f ( s t a t e < 3 && s t a t e > 0) // Checks i f i t s in a worth while s t a t e to do t h i n g s 201 { 202 i f ( s t a t e == 1 && count < 0. 6 ( gtime+rtime 2) ) 203 { 204 statechange. rets = 1 ; 205 statechange. nxts = 2 ; 206 statechange. i n t e r = 2 ; 207 oldcount = count ; 208 } e l s e 209 { 210 statechange. rets = 5 ; 211 statechange. nxts = s t a t e +1; 212 statechange. i n t e r = 2 ; 213 oldcount = 0 ; 214 } 215 i f ( s t a t e == 1) seconds = 0 ; 216 } e l s e i f ( s t a t e == 3) // a l l red s t a t e 217 { 218 statechange. rets = statechange. l t S == 1? 5 : 0 ; 219 statechange. nxts = 4 ; 220 statechange. i n t e r = 2 ; 221 } 222 } 6

7 Appendix D Makefile 1 # AVR Makefile 2 # 3 # Made by S t e f f e n Link 4 5 TRGT = main 6 7 #Source f i l e s 8 SRC = $ ( wildcard. c ) 9 10 # The OBJ macro i s b u i l t from the SRC macro 11 OBJ = $ (SRC :. c =.o ) # Macros f o r the compiler, l i n k e r, and compiler o p t i o n s 14 CC = avr gcc GCC = $ (CC) 16 LINK = $ (CC) 17 MCU = atmega328p 18 CFLAGS = mmcu=$ (MCU) O1 std=c11 #Optimization f o r the delay 19 CXXFLAGS = $ (CFLAGS) 20 DFLAGS = mmcu=$ (MCU) DDEBUG g Og s t d=c PHONY: c l e a n # A macro f o r compiling and f l a s h i n g 25 f u l l : a l l f l a s h # Basic compile 28 a l l : $ (OBJ) 29 $ (GCC) o $ (TRGT) $ (OBJ) $ (CFLAGS) # Add a c l e a n t a r g e t to allow r e b u i l d s 32 c l e a n : 33 rm r f $ (TRGT). o. d. hex $ (OBJ) # Debug compilation 36 debug : CXXFLAGS= $ (DFLAGS) 37 debug : CFLAGS = $ (DFLAGS) 38 debug : $ (OBJ) 39 $ (GCC) o TRGT $ (OBJ) $ (DFLAGS) 40 debug : f l a s h # Remake the p r o j e c t 43 remake : c l e a n 44 remake : a l l # Remake the p r o j e c t w/ debug f l a g s 47 dremake : c l e a n 48 dremake : debug # Flash the AVR 51 f l a s h : 52 avr objcopy $ (TRGT) $ (TRGT). hex 53 avrdude p m328p c arduino b P /dev/ttyusb0 U f l a s h :w: $ (TRGT). hex 7