CSC-2700 – (3) Introduction to Robotics

CSC-2700 – (3) Introduction to Robotics Robotics Research Laboratory Louisiana State University

What we learned in last class • UART – (Universal Asynchronous Receiver/Transmitter) • Minimum required connection (RX,TX, and Ground) • RX – Receiver (yellow) • TX – Transmitter(green) • Ground - black • Our programmer has 2 serial port • ttyACM0 : ISP programming port • ttyACM1 : UART serial port • Wire connection • PE0  Yellow wire • PE1  Green wire • GND  Black wire • Open Gtk-term • Set port : /dev/ttyACM1 • Speed : 57600 for ttyACM1 9600 for Bluetooth connection

Send A2D values through UART • Config.h • Set : #define CFG_USE_UART0 1 • Hardware.h • Set : #define UART0_BAUD_RATE 57600 • ADC_test.c • Add : #include "UART.h” • Create file pointer : FILE *u0; // for UART0 • Open u0 • if defined( __AVR_LIBC_VERSION__ ) • u0 = fdevopen( UART0_PutCharStdio, UART0_GetCharStdio ); • #else • u0 = fdevopen( UART0_PutCharStdio, UART0_GetCharStdio, 0 ); • #endif • Send values using fprintf(u0,”your message %d”, variable); /home/csc2700/csc2700/40-ADC-02

Receiving values from UART • Check the UART buffer first • int UART0_IsCharAvailable() • Read a character from UART buffer • int UART0_GetChar() int counter; char tmpChar; While(1){ if ( UART0_IsCharAvailable() ) { tmpChar = UART0_GetChar(); if ( tmpChar == ‘s'){ // start moving }else if ( tmpChar == ‘c'){ // clear counter }else if ( tmpChar == ‘r’){ // report counter number } } }

Interrupt • Some tasks need to be executed independently from main process • Some tasks need to be executed with specific timing • ADC conversion, UART, PWM, etc • Some tasks need to be executed from arbitrary input signals • external interrupts • Internal / External Interrupts

Types of Interrupts • Internal Interrupt • Timer interrupt • Counter interrupt • ADC, SPM READY(Store Program Memory Ready),EE Ready • External Interrupt • INT0 = SCL [PD0] • INT1 = SDA [PD1] • INT2 = RXD1 [PD2] • INT3 = TXD1 [PD3] • INT4 = OC3B [PE4] • INT5 = OC3C [PE5] • INT6= T3 [PE6] • INT7= ICP3 [PE7] • RESET= RESET [RESET] • SPI, UART, etc

Interrupt Procedure Main program Main program Interrupt occur Interrupt service routine Load PC from Stack then, return to Main program Execute Interrupt Service Routine Interrupt Register Bit check Jump to Triggered Interrupt Vector Interrupt Trigger check Save Main program PC at stack

External Interrupt trigger 1) Falling edge 2) Rising edge High: + 4 V 3) Low level Low: 0.9 V

Interrupt Setting // Grab the rising edge. EICRB |= (( 1 << ISC71 )|( 1 << ISC70 )|( 1 << ISC61 )|( 1 << ISC60 )); // External interrupt control register B EIFR = (( 1 << INTF7 ) | ( 1 << INTF6 )); // External interrup flag register EIMSK |= (( 1 << INT7 ) | ( 1 << INT6 )); // External interrup mask register DDRE &= ~(( 1 << 6 ) | ( 1 << 7 )); // PE6 & PE7 set input PORTE |= (( 1 << 6 ) | ( 1 << 7 )); // pullup for input sei(); // set interrupt cli(); // unset interrupt

Interrupt Service Routine intleftCounter = 0; intprevLeft = 0; intrunFlag = 0; long cnt = 9000000; main(1){ // Grab the rising edge. EICRB |= (( 1 << ISC71 )|( 1 << ISC70 )|( 1 << ISC61 )|( 1 << ISC60 )) // External interrupt control register B EIFR = (( 1 << INTF7 ) | ( 1 << INTF6 )); // External interrup flag register EIMSK |= (( 1 << INT7 ) | ( 1 << INT6 )); // External interrup mask register sei(); // set enable interrupt while(1){ if (leftCounter != prevLeft){ prevLeft = leftCounter; PIN(LED,1,SET_TOGGLE); } while (cnt-- > 0){ } cnt = 9000000; } } // interrupt service routine for int6 SIGNAL(SIG_INTERRUPT6){ leftCounter++; PIN(LED,0,SET_TOGGLE); } // SIG_INTERRUPT6

Let’s make distance measuring program • Make a counter for the optical switches on wheels • Make a clear the counter when ‘c’ message is received from UART • Make a report the counter when ‘r’ message is received from UART • Make a robot move forward when ‘s’ message is received from UART until the counter value is 90

cli() & sei() functions • Interrupts may need to set disable interrupt setting during their job processing • for preventing endless chaining interrupts • for some tasks need no interruption • ADC conversion • Transmitting and receiving procedure • SPI , UART, JTAG, etc • cli() : disable interrupt setting • sei() : enable interrupt setting

External Interrupt & ADC intinterrupt_counter=0; int a2d_value =0; main(1){ while(1){ cli(); // clear interrupt enable set a2d_value = a2d_10(0); // read a2d value sei(); // set enable interrupt fprintf(u0,” a2d= %d, counter = “, a2d_value,interrrupt_counter); delay(500); } } uint16_t a2d_10( uint8_t Channel ){ // Select the channel in a manner which leaves REFS0 and REFS1 un touched. ADMUX = ( ADMUX & (( 1 << REFS1 ) | ( 1 << REFS0 ))) | Channel; // Start the conversion ADCSR = ADCSR | ( 1 << ADSC ); // Wait for it to complete while ( ADCSR & ( 1 << ADSC )); return ADC; // ADC defined at avr/iom128.h ( special function register: SFR_IO16) } // a2d_10

volatile type variable • It allows interrupt processes to read/write global variables even if main process is holding the variables • Special Function Registers(SFR) are defined by volatile type • If interrupt functions and the main function share a global variable, you should define the variable as volatile type - read/write failure

Optical Switch • Consideration for using optical switch on interrupt pins Case 1 Case 2 Case 3 IR detector Black Bar Output : 0 Output : 1 Output : 0 or 1

CSC-2700 – (3) Introduction to Robotics