Embedded Systems and Software

Transcription

1 Embedded Systems and Software Lab 5 Considerations Lab 5 Considerations Slide 1

2 Big Picture Keypad Mag-Stripe Card Reader User PINs are stored in μμμμ FLASH memory Swipe Card LCD Lab 5 Considerations Slide 2

3 Major Elements Read User-IDs from Mag Stripe reader Read PINs from Keypad Compare the entered USER-IDs and PINs to values stored in FLASH Display text on LCD Central Issues Where to Start? o Timers o Keypad, Mag-Stripe o Interrupts Usually a good idea to consider timing constraints first This will dictate the overall structure of the application Lab 5 Considerations Slide 3

4 Mag Stripe Reader Lab 5 Timing Constraints Nominal data rate: 1.5 ms/bit (= 667 Hz) Data must be sampled within ~ 0.75 ms after leading edge of strobe Lab 5 Considerations Slide 4

5 Keypad Lab 5 Timing Constraints Switch debounce requires sampling keypad at ~ 10 ms intervals Variation of a few ms in either direction can be tolerated LCD Writing a character to the LCD requires known time Need to insure that programmed delays don t interfere with servicing of other devices e.g., How long does it take to write 16 characters to the LCD? Lab 5 Considerations Slide 5

6 Main Program Loop: How Should Lab 5 be Structured? Authorize Users: check entered User-ID/PIN against values stored in FLASH Service LCD Mag Stripe Reader Service via external interrupt Should be OK to trigger interrupts on leading edge of strobe Keypad Service via periodic timer interrupt 10 ms period should work OK Lab 5 Considerations Slide 6

7 One Possible Structure of Program Main Program Loop Authorize Users: check entered User-ID/PIN against values stored in FLASH Service LCD Mag Stripe Reader Should be OK to trigger interrupts on leading edge of strobe Service via external interrupt Service via periodic timer interrupt 10 ms period should work OK Keypad Lab 5 Considerations Slide 7

8 One Possible Structure of Program Timer ISR Reads keypad on rollover, every 10 ms Main Program Authenticates IDs/PINs Services LCD External Interrupt ISR Reads Mag-Stripe Data ISR is invoked at leading-edge of each strobe cycle (approx. the middle of each data bit period) from the mag-stripe reader ISR must sample the data line from the mag-stripe reader and assemble and store digits read from track 2 Lab 5 Considerations Slide 8

9 Track 2 Format Odd Parity b3 b2 b1 b0 Meaning of Group Track 2 data characters are 4 bits + parity. Must be numeric: 0x0 0x9) Lab 5 Considerations Slide 9

10 Track 2 Format Odd Parity b3 b2 b1 b0 Meaning of Group Characters are recorded LSb first with parity at the end i.e., right to left in this diagram Lab 5 Considerations Slide 10

11 Track 2 Format Odd Parity b3 b2 b1 b0 Meaning of Group The data output from the stripe reader is inverted. Logical zeros will be read as high values, logical ones as low. Lab 5 Considerations Slide 11

12 Mag-Stripe Reader ISR Game Plan Identify the beginning of the start sentinel Assemble next four bits into a digit and store in an array Read the parity bit and discard (or verify correct parity) Continue to assemble and store digits as above until the 10-digit User-ID, stop sentinel, and LRC character have been read But, remember, this behavior takes place over many invocations of the ISR the ISR is invoked once for each bit-time on the card Lab 5 Considerations Slide 12

13 Useful Tool Finite State Machine data = 0 (high) S0 Waiting for Start Sentinel Structure the Mag-reader ISR as a FSM one state transition per invocation Lab 5 Considerations Slide 13

14 Useful Tool Finite State Machine data = 0 (high) S0 Waiting for Start Sentinel data = 1 (low) S1 First bit of char read Structure the Mag-reader ISR as a FSM one state transition per invocation Lab 5 Considerations Slide 14

15 Useful Tool Finite State Machine data = 0 (high) S0 S1 S2 Waiting for Start Sentinel data = 1 (low) First bit of char read data = x Second bit of char read Structure the Mag-reader ISR as a FSM one state transition per invocation Lab 5 Considerations Slide 15

16 Useful Tool Finite State Machine data = 0 (high) S0 S1 S2 Waiting for Start Sentinel data = 1 (low) First bit of char read data = x Second bit of char read data = x S3 Third bit of char read Structure the Mag-reader ISR as a FSM one state transition per invocation Lab 5 Considerations Slide 16

17 Useful Tool Finite State Machine data = 0 (high) S0 S1 S2 Waiting for Start Sentinel data = 1 (low) First bit of char read data = x Second bit of char read data = x data = x S4 Fourth bit of char read data = x S3 Third bit of char read Structure the Mag-reader ISR as a FSM one state transition per invocation Lab 5 Considerations Slide 17

18 Useful Tool Finite State Machine data = 0 (high) S0 S1 S2 Waiting for Start Sentinel data = 1 (low) First bit of char read data = x Second bit of char read last char (LRC) has been read S5 Parity bit read data = x data = x; last char was not LRC S4 Fourth bit of char read data = x S3 Third bit of char read data = x Structure the Mag-reader ISR as a FSM one state transition per invocation Lab 5 Considerations Slide 18

19 #define S0 0 #define S1 1 #define S2 2 #define S3 3 #define S4 4 #define S5 5 char next_state = S0; char current_bit; char next_bit; char ch; char User_ID[12]; Implementing FSM ISR is invoked for each bit the reader sees Mag_Stripe_ISR() { current_bit = next_bit next_bit = /* read Mag stripe data */ switch (next_state){ S0: if (next_bit == 0) next_ state = S0; else next_state = S1; break; S1: next_state = S2; break;. : S5: if (/* 12 chars have been read */) next_state = S0; else next_state = S1; } } Lab 5 Considerations Slide 19

20 #define S0 0 #define S1 1 #define S2 2 #define S3 3 #define S4 4 #define S5 5 char next_state = S0; char current_bit; char next_bit; char ch; char User_ID[12]; Implementing FSM #define for the states Mag_Stripe_ISR() { current_bit = next_bit; next_bit = /* read Mag stripe data */ switch (next_state){ S0: if (next_bit == 0) next_ state = S0; else next_state = S1; break; S1: next_state = S2; break;. : S5: if (/* 12 chars have been read */) next_state = S0; else next_state = S1; } } Lab 5 Considerations Slide 20

21 #define S0 0 #define S1 1 #define S2 2 #define S3 3 #define S4 4 #define S5 5 char next_state = S0; char current_bit; char next_bit; char ch; char User_ID[12]; Mag_Stripe_ISR() { current_bit = next_bit; next_bit = /* read Mag stripe data */ switch (next_state){ S0: if (next_bit == 0) next_ state = S0; else next_state = S1; break; S1: next_state = S2; break;. : S5: if (/* 12 chars have been read */) next_state = S0; else next_state = S1; } } Implementing FSM Read bit value (1 or 0) from the card reader Lab 5 Considerations Slide 21

22 #define S0 0 #define S1 1 #define S2 2 #define S3 3 #define S4 4 #define S5 5 char next_state = S0; char current_bit; char next_bit; char ch; char User_ID[12]; Mag_Stripe_ISR() { current_bit = next_bit; next_bit = /* read Mag stripe data */ switch (next_state){ S0: if (next_bit == 0) next_ state = S0; else next_state = S1; break; S1: next_state = S2; break;. : S5: if (/* 12 chars have been read */) next_state = S0; else next_state = S1; } } Implementing FSM Do different things depending of what state we are at Lab 5 Considerations Slide 22

23 #define S0 0 #define S1 1 #define S2 2 #define S3 3 #define S4 4 #define S5 5 char next_state = S0; char current_bit; char next_bit; char ch; char User_ID[12]; Mag_Stripe_ISR() { current-bit = next_bit; next_bit = /* read Mag stripe data */ switch (next_state){ S0: if (next_bit == 0) next_ state = S0; else next_state = S1; break; S1: next_state = S2; break;. : S5: if (/* 12 chars have been read */) next_state = S0; else next_state = S1; } } Implementing FSM Do state 0 s work here Lab 5 Considerations Slide 23

24 #define S0 0 #define S1 1 #define S2 2 #define S3 3 #define S4 4 #define S5 5 char next_state = S0; char current_bit; char next_bit; char ch; char User_ID[12]; Mag_Stripe_ISR() { current-bit = next_bit next_bit = /* read Mag stripe data */ switch (next_state){ S0: if (next_bit == 0) next_ state = S0; else next_state = S1; break; S1: next_state = S2; break;. : S5: if (/* 12 chars have been read */) next_state = S0; else next_state = S1; } } Implementing FSM Do state 2 s work here Lab 5 Considerations Slide 24

25 Possible Lab 5 Program Structure External Interrupt ISR Mag-Stripe Main Loop Authenticates IDs/PINs Services LCD Timer ISR Reads Keypad Lab 5 Considerations Slide 25

26 Possible Lab 5 Program Structure char Card_Swiped External Interrupt ISR Mag-Stripe char ID[10] Main Loop Authenticates IDs/PINs Services LCD Timer ISR Reads Keypad Lab 5 Considerations Slide 26

27 Possible Lab 5 Program Structure char Card_Swiped External Interrupt ISR Mag-Stripe char ID[10] Main Loop Authenticates IDs/PINs Services LCD Timer ISR Reads Keypad ISR sets Card_Swiped to indicate that a complete User-ID has been read from a card. The User-ID is placed by the ISR into the array ID Lab 5 Considerations Slide 27

28 Possible Lab 5 Program Structure char Card_Swiped char PIN_Entered External Interrupt ISR Mag-Stripe char ID[10] Main Loop Authenticates IDs/PINs Services LCD char PIN[4] Timer ISR Reads Keypad ISR sets Card_Swiped to indicate that a complete User-ID has been read from a card. The User-ID is placed by the ISR into the array ID Lab 5 Considerations Slide 28

29 Possible Lab 5 Program Structure char Card_Swiped char PIN_Entered External Interrupt ISR Mag-Stripe char ID[10] Main Loop Authenticates IDs/PINs Services LCD char PIN[4] Timer ISR Reads Keypad ISR sets Card_Swiped to indicate that a complete User-ID has been read from a card. The User-ID is placed by the ISR into the array ID ISR sets PIN_Entered to indicate that a complete PIN has been read from the keypad. The PIN is placed by the ISR into the array PIN Lab 5 Considerations Slide 29

30 Main Program as a FSM!(Card_Swiped) A_IDLE Lab 5 Considerations Slide 30

31 Main Program as a FSM!(Card_Swiped) CHECK_ID A_IDLE invalid ID Lab 5 Considerations Slide 31

32 Main Program as a FSM!(Card_Swiped)!(PIN_Entered) CHECK_ID valid ID GET_PIN A_IDLE invalid ID Lab 5 Considerations Slide 32

33 Main Program as a FSM!(Card_Swiped)!(PIN_Entered) CHECK_ID valid ID GET_PIN A_IDLE invalid ID bad PIN PIN_Entered CHECK_PIN Lab 5 Considerations Slide 33

34 Main Program as a FSM!(Card_Swiped)!(PIN_Entered) CHECK_ID valid ID GET_PIN A_IDLE invalid ID bad PIN PIN_Entered AUTHORIZE valid PIN CHECK_PIN < five seconds Lab 5 Considerations Slide 34

35 Main Program as a FSM!(Card_Swiped)!(PIN_Entered) CHECK_ID valid ID GET_PIN A_IDLE invalid ID bad PIN PIN_Entered five seconds elapsed AUTHORIZE valid PIN CHECK_PIN < five seconds Lab 5 Considerations Slide 35

36 Pseudo-Code for Main FSM states main () { //Initialization Goes Here while(1) switch (Auth_Next_State) { A_IDLE: /* A_IDLE State Stuff Goes Here */ break; CHECK_ID: /* CHECK_ID State Stuff Goes Here */ break; GET_PIN: /* GET_PIN State Stuff Goes Here */ break; CHECK_PIN: /* CHECK_PIN State Stuff Goes Here */ break; AUTHORIZE: /* AUTHORIZE State Stuff Goes Here */ } Lab 5 Considerations Slide 36

37 Pseudo-Code for Main FSM states Initialization: Display Swipe Card on LCD; Turn off Authorization LED; Card_Swiped = false; PIN_Entered = false; Auth_Next_State = A_IDLE; IDLE: if (Card_Swiped) Auth_Next_State = CHECK_ID; else Auth_Next_State = A_IDLE; break; Lab 5 Considerations Slide 37

38 Pseudo-Code for Main FSM states CHECK_ID: Reset Card_Swiped; if (ID matches a stored User-ID) { Stored_PIN = PIN of matching stored User-ID; Display Enter PIN on LCD; Auth_Next_State = GET_PIN; } else { Display Invalid ID on LCD Auth_Next_State=A_IDLE; } break; GET_PIN: if (PIN_Entered) Auth_Next_State = CHECK_PIN; else Auth_Next_State = GET_PIN; break; Lab 5 Considerations Slide 38

39 Pseudo-Code for Main FSM states AUTHORIZE: if ( less than five seconds have elapsed since entering this state) Auth_Next_State = AUTHORIZE; else { Turn off authorization LED; Display Swipe Card on LCD; Auth_Next_State = A_IDLE; } break: CHECK_PIN: if (PIN == Stored_PIN) { Turn on Authorization LED; Display Door is Unlocked on LCD; Auth_Next_State = Authorize; } else { Display Re-enter PIN on LCD; Auth_Next_State = GET_PIN; } break; Lab 5 Considerations Slide 39

40 Lab 5 Considerations Slide 40