64 lines
2.3 KiB
C
64 lines
2.3 KiB
C
#include <avr/io.h>
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#include <util/delay.h>
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#include <avr/interrupt.h>
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#include "utils.h"
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#include "bitmanip.h"
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#include "timer.h"
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#include "usart.h"
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#include "interrupt.h"
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// TIMER
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#define PERIOD 2000
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#define PRESCALE_VALUE 1024 // can be 1, 8, 64, 256, 1024
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// USART
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#define USART_BAUDRATE 115200 // Table 20-1 : Baud Rate Calculation
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// END MACROS
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void uart_init() {
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UBRR0H = (unsigned char) (BAUD_PRESCALER(USART_BAUDRATE) >> 8); // 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
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UBRR0L = (unsigned char) BAUD_PRESCALER(USART_BAUDRATE);
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UCSR0C |= ASYNCHRONOUS | PARITY_DISABLED | STOP_ONE_BIT | DATA_EIGHT_BIT; // 20.11.4 : set Frame Format
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UCSR0B |= RECEIVER_DISABLED | TRANSMITTER_ENABLED; // 20.11.3 : enable Receiver and/or Transmitter
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}
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void uart_tx(char c) {
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while (TEST(UCSR0A, UDRE0) == 0); // 20.11.2 : do nothing until UDR emission buffer is empty, if UDREn flag is 1, UCSRnA register is empty
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UDR0 = (unsigned char) c; // 20.11.1 : Put data into buffer, UDRn – USART I/O Data Register (read and write)
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}
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void uart_printstr(const char* str) {
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while (*str) {
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uart_tx(*str);
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str++;
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}
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}
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// print "Hello World!\n", on serial port, every 2 seconds, with empty infinite loop
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// `screen /dev/ttyUSB0 115200`
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int main() {
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uart_init();
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TCCR1A |= CTC_TOP_OCR1A_IN_TCCR1A; // Table 16-4 : set timer in CTC (Clear Time on Compare) mode
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TCCR1B |= CTC_TOP_OCR1A_IN_TCCR1B;
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SREG |= ENABLE_GLOBAL_INTERRUPT; // 7.3.1 : Status Register, bit 7 : I – Global Interrupt Enable
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TIMSK1 |= INTERRUPT_ENABLE_CHANNEL_A; // 16.11.8 : enables the Timer1 Compare Match A interrupt, this makes the MCU react when OCR1A == TCNT1 by calling TIMER1_COMPA_vect
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OCR1A = TIME_MS(PERIOD, PRESCALE_VALUE); // Table 16-4 : set CTC compare value on channel A, the counter is cleared to zero when the counter value (TCNT1) matches the OCR1A register
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TCCR1B |= (PRESCALE_SET(PRESCALE_VALUE)); // 16.4 : set timer according to prescale value, in register TCCR1B, table 16-5 : prescale sets
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while(1);
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}
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// ISR interrupt macro : https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html
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ISR(TIMER1_COMPA_vect) { // Table 12-7 : we select the code for timer 1 on channel A
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uart_printstr("Hello World!\r\n"); // \n and \r : https://stackoverflow.com/questions/7812142/how-to-toggle-cr-lf-in-gnu-screen
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}
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