cs 212 dick steflik n.
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Butterfly I/O Ports

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Butterfly I/O Ports

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  1. CS-212 Dick Steflik Butterfly I/O Ports

  2. I/O for our labs • To get data into and out of our Butterfly its a little trickier than using printf and scanf as you did in CS211 • Since the Butterfly doesn't have an Operating System we need to write and read data directly to/from the I/O ports • Access to the ports is through the Special Function Registers (SFRs) that are defined symbolically in iom169.h which is included in your program by io.h

  3. io.h # include <avr/iom165p.h> #elif defined (__AVR_ATmega168__)‏ # include <avr/iom168.h> #elif defined (__AVR_ATmega168P__)‏ # include <avr/iom168p.h> #elif defined (__AVR_ATmega169__)‏ # include <avr/iom169.h> #elif defined (__AVR_ATmega169P__)‏ # include <avr/iom169p.h> #elif defined (__AVR_ATmega8HVA__)‏ # include <avr/iom8hva.h> #elif defined (__AVR_ATmega16HVA__)‏

  4. iom169.h /* iom169.h - definitions for ATmega169 */ /* This should be up to date with data sheet version 2514J-AVR-12/03. */ #ifndef _AVR_IOM169_H_ #define _AVR_IOM169_H_ 1 /* This file should only be included from <avr/io.h>, never directly. */ #ifndef _AVR_IO_H_ # error "Include <avr/io.h> instead of this file." #endif #ifndef _AVR_IOXXX_H_ # define _AVR_IOXXX_H_ "iom169.h" #else # error "Attempt to include more than one <avr/ioXXX.h> file." #endif /* I/O registers */ /* Port A */ #define PINA _SFR_IO8(0x00)‏ #define DDRA _SFR_IO8(0x01)‏ #define PORTA _SFR_IO8(0x02)‏ /* Port B */ #define PINB _SFR_IO8(0x03)‏ #define DDRB _SFR_IO8(0x04)‏

  5. sfr_defs.h • included in every compile via io.h • contains macro definitions for accessing Special Function Registers as if they were just c language variables • in iom169.h the statement: #define PINA _SFR_IO8(0x00) the symbol PINA is mapped to the SFR at address 0x00 in SFR memory • _SFR_IO8( ) is a macro (look in sfr_defs.h )‏

  6. Why this is done • in your program you #include io.h and io.h in turn includes iom169.h (because in your project definition you picked the ATmega169 as the processor)‏ • pass 1 of the compiler does all includes and macro substitutions ( in our example with PINA all occurrences of the symbol PINA in your program will be replaced with a reference to SFR 0x00)‏ • This makes all SFR references look like references to C variables

  7. Memories

  8. Getting Data Into and Out Of • Initialize the ports • set the Data Direction Registers (DDRs)‏ • use PORTB for input • use the 8 input DIP switch for inputting data • don't forget the pull-up resistors • use PORTD for showing output • use 8 LEDS • don't forget the current limiting, series resistors

  9. Design • This warrants 3 subroutines • one to do initialization • one to do input • one to do output • These should be written very general purpose as we will use them for many of the labs

  10. daemons • a daemon is a program that will sit in memory forever and run until the system loses power • since most embedded system run forever (until they lose power) our main() should be written as a never ending loop. • processing to be done can be done either in the body of the loop or asynchronously in response to an external or internal event (interrupt)‏

  11. Interrupts • How Interrupts are handled • Somewhere in your program you define an Interrupt Servicing Subroutine, the compiler will put the address of this routine into the proper location in the interrupt vector (low memory)‏ • When the interrupt occurs the system state is saved, a branch to the ISS is made via the interrupt vector • The ISS executes and returns the state of the system and you are right where you were before the interrupt occurred

  12. ATmega169 Interrupt Vector

  13. What we want to do • use 8 LEDs for output • 8 switches for input • 1 button to tell when it is OK to read the switches • to do this we should us an interrupt

  14. The way it should work /* Interrupt handler */ { // disable interruptes // read the switches // save the data at the next location in an array // light the lights // enable interrupts } int main ()‏ { // initialize ports B & D // initial Port E for interrupt on PE2 // loop forever – this is our daemon }

  15. volatile keyword • the keyword “volatile” should be used to define any variable that may be modified inside of an interrupt handler • “volatile” flags a variable to the optimizing compiler to not optimize variables with the “volatile” keyword volatile char switches = 0; volatile uint8_t flags = 0;

  16. char & uint8_t • Remember the char data type can be used for ASCII characters or a signed 8 bit integer • The AVR header files define another data type that allows an unsigned 8 bit integer, this is convenient for working with gpio ports as they are not usually signed data.

  17. internal pullups for gpio inputs • on many MCUs you must add an external pullup resistor on gpio input lines • Atmel MCUs have built-in internal pullup resistors • to use the internal pullups write a one to that line after it has been defined as an input line in the DDR // define Port B as all outputs and Port D as all inputs DDRB = 0xFF; DDRD = 0x00; //turn on the internal pullup resistors for Port D PORTD = 0xFF;

  18. Setting up an interrupt handler • Signal or ISR • the ISR macro has superceded the Signal macro and is the preferred way of setting up an interrupt handler ISR( name of the int from processor .h file)‏ { ........ } ISR(SIG_PIN_CHANGE1)‏ { .... }

  19. Pin Change Interrupts • Input lines on Ports B and E can be set up to generate a pin change interrupt • Each port has an associated mask register • to enable an interrupt put a 1 into the correct position in the appropriate mask register • Port B PCMSK1 • Port E PCMSK0


  21. Example //set bit 2 of Port B to cause an interrupt PCMSK1 = 0x04; // set bit 2 of Port B to cause interrupt EIMSK = 0xC0; // Ext Int Mask Reg EIFR = 0xC0; // Ext Int Flag Reg DDRB & = 0xFB; // make bit 2 an input line PORTB | = 0x04; // turn on pullup ISR(SIG_PIN_CHANGE1)‏ { cli( ); // disable interrupts . . . sei( ); // enable interrupts }