Iii avr-basics(2)

Microprocessor based Design for Biomedical Applications

MBE 3 – MDBA

III : The ATmega8 Basic Features (2)

Let‘s repeat some important topics of the last lecture:

AVR memoriesSFRs – GFRsBit OperationsGPIO PortsClock SourcesInterrupt Handling

Today:

Fix the IDE – Bug (update AVR-Studio)Repeat blink.c sourceUse the SimulatorLook at avr-gcc, avr-objdump, make ISR – Interrupt Service RoutinesTimer Interrupt Example16-Bit Timer, ModesUART – Configuration and ModesStart with Uart Example

Blink.c – sourcecode review

#include <avr/io.h> #include <util/delay_basic.h>

#define Bit(x) (1<<x)

void delay_ms(uint16_t ms){ uint16_t t; for (t=0;t<ms;t++) _delay_loop_2(1843); // 1843 * 4 clock cycles gives 7372 cycles: // (approx. 1 millisecond at 7,3728 MHz}

int main( void ){ DDRD = Bit(5); // DataDirection Port D: Pin D5 = Output (Led) PORTD= Bit(5); // Switch on led and deactivate pullups on the inputs

while (1) { PORTD ^= Bit(5); // toggle D5 delay_ms(500); // wait 500 milliseconds }return(0);}

Macro definition, shift left operation

Function definition, call by value (call by reference: pointer)

SFRs for Port D configuration

Bit manipulation Port D (XOR)

Include device specific definitions (SFRs,..)

Using the AVRStudio - Simulator

additional information to the Getting_Started.pdf

Flow Control Peripherals

Peripheral Details

CPUstatus

AVRStudio SimulatorOverview


Breakpoint

Watch Window


Register and Memory Views

Watch Window

Disassembly Window

AVRStudio Simulator notes

● Select the Crystal / Oscillator frequency to get accurate time measurements in the Simulator

● beware of delay loops (they take long to simulate)

● use „run to cursor“ or breakpoints for getting into interrupt handlers

● on-chip debugging is useful, needs devices with JTAG interface or debugWire interface

Using the WinAVR-Toolchain from commandline

WinAVR-Toolchain – avr-gcc.exe

Compile

Link

Convert .elf to .ihex

Download to Device

.elf: Executable and Linking Format, segment and section information

WinAVR-Toolchain – make.exeMAKEFILE The makefile automates the build process only changed modules are compiled

Environment variables add flexibility

current target

current prerequistite

Browse the GNU MAKE User Manual: http://www.gnu.org/software/make

Rules

Variables & constants

Target

SRC = blink.c test.cCFLAGS= -O2 -g -Wall

PRG = $(SRC:.c=.hex)

all: $(PRG)

# Create .hex files from .o files%.hex : %.o

echo Creating $@avr-objcopy -O ihex $< $@

# Compile%.o : %.c

echo Compiling $@avr-gcc $(CFLAGS) -mmcu=atmega8 $< -o $@

clean:rm -f *~ *.bak *.lst *.o *.hexc

WinAVR-Toolchain – avr-objdump.exe

Avr-objdump:

Extract informationfrom .elf – file

Here: show disassembly information

Where to find AVR C - specific information ?

● AVR-GCC is ANSI-C compatible

● browse the AVR Libc – Documentation

● examine module header files (#include <…>) subdirectory avr/include

● use example code, play with open source firmware


<assert.h>: Diagnostics <ctype.h>: Character Operations <errno.h>: System Errors <inttypes.h>: Integer Type conversions <math.h>: Mathematics <stdint.h>: Standard Integer Types <stdio.h>: Standard IO facilities <stdlib.h>: General utilities <string.h>: Strings, memory functions<avr/boot.h>: Bootloader Support Utilities <avr/eeprom.h>: EEPROM handling <avr/interrupt.h>: Interrupts <avr/pgmspace.h>: Program Space Utilities<avr/power.h>: Power Reduction Management<avr/io.h>: Special function registers and IO definitions<avr/sleep.h>: Power Management and Sleep Modes<util/delay_basic.h>: Basic busy-wait delay loops <util/parity.h>: Parity bit generation<util/twi.h>: TWI bit mask definitions

Useful modules,all documented inthe AVR-Libc manual !


• typedef signed char int8_t• typedef unsigned char uint8_t• typedef signed int int16_t• typedef unsigned int uint16_t• typedef signed long int int32_t• typedef unsigned long int uint32_t• typedef signed long long int int64_t• typedef unsigned long long int uint64_t

#define INT8_MAX 0x7f#define INT8_MIN (-INT8_MAX - 1)

…

Standard integer and character types, defined in <stdint.h>: 8, 16, 32 and 64 bit, signed and unsigned

Constants for min and max values


• void memcpy (void , const void , size_t)• void memmove (void , const void , size_t)• char strcat (char , const char )• char strstr (const char , const char )• char strupr (char )…

Some functions from <string.h>:

Interrupt handling with the AVR-Libc API

Interrupt and Signal definitions: <avr/interrupt.h>

● remember: vector table points to interrupt routines

● by using the appropriate name, your routine will be installed in the table and called when the interrupt occurs

● a set of default interrupt routines is provided

● Macro for registering interrupt routines: ISR (<signalname>)

● saving and restoring registers is handled


Examle interrupt handler for the ADC:

#include <avr/interrupt.h>

ISR(ADC_vect) { // user code here } ● The interrupt source, here the ADC, has to be configured and enabled using SFRs

● Global interrupt instructions: sei () … set interupt enable (I – bit in SREG) cli () … clear interrupt enable

● AVR hardware clears the global interrupt flag before entering an interrupt vector -> use sei() to enable nested interrupts


Useful Interrupt vector names for ATmega8:

ADC_vect analog/digital converter ANA_COMP_vect analog comparator EE_RDY_vect eeprom ready INT0_vect external interrupt 0 TIMER0_OVF_vect Timer0 overflow event TIMER1_CAPT_vect Timer1 capture event SPI_STC_vect serial transfer complete USART_UDRE_vect USART data register empty USART_RXC_vect USART receive complete

more AVR Peripheral Features

16 – bit Timer / Counter 1

● Two Independent Output Compare Units● can be used as Pulse Width Modulator (PWM)● Clear Timer on Compare Match (Auto Reload)● One Input Capture Unit● can be used as External Event Counter● Four Independent Interrupt Sources TOV1, OCF1A, OCF1B, and ICF1


● TCNT1, OCR1A, OCR1B and ICR1 are 16-bit registers

● write high byte first read low byte first (automatically done in C)

● clocking via prescaler or external clock on pin T1

● output compare register OCR1A/B can be used for PWM generation (output pin: OC1A/B) or for interrupt request


● Input capture Unit: timestamp external events on ICP1 pin (or on Analog comp.) Can generate Input Capture Interrupt


● Output Compare Units: compare TCNT1 with OCR1A and OCR1B Can generate Output Capture Interrupt

● 13 PWM / Waveform generation modes

● Top and Bottom values

● Auto reload


● Mode configuration using TCCR1A and TCCR1B

PWM Mode, set/clear/toggle of OC1A/B, auto-reload, Noise canceller

Find Details in the ATmega8 datasheet !


● Clock source configuration using TCCR1B

The UART Serial Interface

USART interface

● universal synchronous / asynchronous receiver / transmitter

● Full Duplex Operation: Receive and Transmit Registers

● Asynchronous or Synchronous Operation

● Frames with 5, 6, 7, 8, or 9 Databits and 1 or 2 Stop Bits

● Odd or Even Parity Generation and Parity Check

● Framing Error Detection, Noise Filtering

● Interrupts possible on TX Complete, TX Data Register Empty and RX Complete

USART interface

● synchronous mode: Pin XCK is used as clock Input (slave) or clock output (master)

● asynchronous mode: receiver and transmitter are clocked independently

USART interface

● Frame formats:

USART interface

● calculating the baud rate register value:

low and high byte of ubrr are written into the UBRRL and UBRRH registers

Accuracy depends on System clock source !

(see table in ATmega8 data sheet, pp 155)

USART interface

● Initialisation: set baud rate, frame format, enable TX and RX

RXC: RX completeTXC: TX completeUDR: Uart Data Register emptyFE: Frame ErrorDOR: Data OverRunPE: Parity ErrorU2X: Double the USART speed

USART interface


RXCIE: RX complete interrupt enableTXCIE: TX complete interrupt enableUDRIE: Uart Data Register empty interrupt enableRXEN: Receiver EnableTXEN: Transmitter EnableUCSZ2: Character SizeRXB8, TXB8: Bit 8 for receive and transmit

USART interface


URSEL: Register Select (1=UCSR/0=UBRRH)UMSEL: 0=async. mode, 1=sync. ModeUMP1, UMP0: Parity mode: 00 = disabled, 10 = even, 11=oddUSBS: Stop Bits: 0=1 Stop Bit, 1= 2 Stop bitsUCSZ2,1, 0 : character size

USART interface

character size selection using the UCSZ bits

USART interface

Selection of the baud rate using the UBRRH and UBRRL SFRs:

URSEL has to be 0 when writing to the UBRRH register

USART interface


void USART_Init( unsigned int baud ){ /* Set baud rate */ UBRRH = (unsigned char)(baud>>8); UBRRL = (unsigned char)baud;

/* Set frame format: 8data, 2stop bit */ UCSRC = (1<<URSEL)|(1<<USBS)|(3<<UCSZ0);

/* Enable Receiver and Transmitter */ UCSRB = (1<<RXEN)|(1<<TXEN);

}

USART interface

● Sending bytes in polling mode

void USART_Transmit( unsigned char data ){ /* Wait for empty transmit buffer */ while ( !( UCSRA & (1<<UDRE)) );

/* Put data into buffer, sends the data */ UDR = data;}

USART interface

● Receiving bytes in polling mode

unsigned char USART_Receive( void ){ /* Wait for data to be received */ while ( !(UCSRA & (1<<RXC)) ) ;

/* Get and return received data from buffer */ return UDR;}

Iii avr-basics(2)

Engineering

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