Butterfly I/O Ports

CS-212Dick Steflik

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

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__)

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)

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 )

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

Memories

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

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

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)

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

ATmega169 Interrupt Vector

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

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}

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;

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.

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 inputsDDRB = 0xFF;DDRD = 0x00;//turn on the internal pullup resistors for Port DPORTD = 0xFF;

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){ ....}

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

PCINT Mapping PORT EPCINT7 7 SIG_PIN_CHANGE0PCINT6 6PCINT5 5PCINT4 4PCINT3 3PCINT2 2PCINT1 1PCINT0 0

PORT BPCINT15 7 SIG_PIN_CHANGE1PCINT14 6PCINT13 5PCINT12 4PCINT11 3PCINT10 2PCINT9 1PCINT8 0

Example

//set bit 2 of Port B to cause an interruptPCMSK1 = 0x04; // set bit 2 of Port B to cause interruptEIMSK = 0xC0; // Ext Int Mask RegEIFR = 0xC0; // Ext Int Flag RegDDRB & = 0xFB; // make bit 2 an input linePORTB | = 0x04; // turn on pullup

ISR(SIG_PIN_CHANGE1){ cli( ); // disable interrupts . . . sei( ); // enable interrupts }