├── serial.cpp
├── serial.h
└── test.cpp


/serial.cpp:
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 1 | #include <avr/interrupt.h>
 2 | #include <util/delay.h>
 3 | #include "serial.h"
 4 | 
 5 | void serial_init() {
 6 |   #ifdef SERIAL_SEND
 7 |     DDRB |= 1 << SERIAL_SEND; // Set transmit as output
 8 |     PORTB |= 1 << SERIAL_SEND; // Set high (inactive)
 9 |   #endif
10 | 
11 |   #ifdef SERIAL_RECEIVE
12 |     DDRB &= ~(1 << SERIAL_RECEIVE);
13 | 
14 |     TCCR0A |= 1 << WGM01; // clear on compare
15 |     TCCR0B |= (1 << CS01) | (1 << CS00); // set timer clock to 0b011 (clock/64)
16 | 
17 |     GIMSK = 1 << PCIE; // general intertupt mask enable pin change int
18 |     PCMSK |= 1 << SERIAL_RECEIVE; // Pin change mask?
19 |     sei(); // set int enabled
20 |   #endif
21 | }
22 | 
23 | #ifdef SERIAL_SEND
24 |   void serial_send(unsigned char val) {
25 |     PORTB &= ~(1 << SERIAL_SEND); // Set low
26 |     _delay_us(1000000 / SERIAL_RATE); // Wait
27 | 
28 |     for (char i = 0; i < 8; ++i) { // Loop bits
29 |       PORTB = (PORTB & ~(1 << SERIAL_SEND)) | (((val >> i) & 1) << SERIAL_SEND); // Set port to each bit
30 |       _delay_us(1000000 / SERIAL_RATE); // Wait
31 |     }
32 | 
33 |     PORTB |= 1 << SERIAL_SEND; // Send stop bit
34 |     _delay_us(1000000 / SERIAL_RATE); // Wait
35 |   }
36 | #endif
37 | 
38 | #ifdef SERIAL_RECEIVE
39 |   volatile unsigned char position; // Current position within byte
40 |   volatile unsigned char data; // Recieved byte
41 | 
42 |   /*
43 |     WARNING: Receive uses inverted logic, designed to be used with an inverting level shifter
44 |   */
45 |   ISR(TIM0_COMPA_vect) { // Timer interrupt
46 |     if (!(PINB & (1 << SERIAL_RECEIVE))) { // If current bit is set
47 |       data |= (1 << position); // Set corresponding bit in recieved byte
48 |     }
49 | 
50 |     if (++position == 8) { // If at end of byte
51 |       TIMSK0 &= ~(1 << OCIE0A); // Disable interrupt for compare register A (this interrupt)
52 |       serial_receive(data); // Alert user they have data
53 |       PCMSK |= 1 << SERIAL_RECEIVE; // Enable pin change interrupt to start next byte
54 |     } else {
55 |       OCR0A = SERIAL_BIT_TIME; // Set delay time equal to the length of a single bit
56 |     }
57 |   }
58 | 
59 |   /*
60 |     WARNING: Receive uses inverted logic, designed to be used with an inverting level shifter
61 |   */
62 |   ISR(PCINT0_vect) { // On pin change
63 |     if (PINB & (1 << SERIAL_RECEIVE)) { // If is a start bit
64 |       TCNT0 = 0; // Set counter to 0
65 |       OCR0A = SERIAL_BIT_TIME * 1.5; // Call timer interrupt in middle of first bit
66 |       position = 0; // Reset position and data
67 |       data = 0;
68 |       TIMSK0 |= 1 << OCIE0A; // Enable interrupt for compare register A (timer interrupt)
69 |       TIFR0 |= 1 << OCF0A; // Clear timer interrupt flag to prevent it jumping directly there
70 |       PCMSK &= ~(1 << SERIAL_RECEIVE); // Disable pin change interrupt
71 |     }
72 |   }
73 | #endif
74 | 


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/serial.h:
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 1 | #define SERIAL_SEND 3
 2 | #define SERIAL_RECEIVE 4
 3 | #define SERIAL_RATE 9600
 4 | 
 5 | #define SERIAL_BIT_TIME (1000000.0 / SERIAL_RATE) / (1.0 / 9.6 * 64)
 6 | 
 7 | void serial_init();
 8 | 
 9 | #ifdef SERIAL_SEND
10 |   void serial_send(unsigned char data);
11 | #endif
12 | 
13 | void serial_receive(unsigned char data);
14 | 


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/test.cpp:
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 1 | #include "serial.h"
 2 | 
 3 | unsigned char buffer[10]; // 10 byte buffer
 4 | 
 5 | int main() {
 6 |   serial_init(); // Initialise UART
 7 | 
 8 |   while(1); // Do a heap of useful calculations
 9 | }
10 | 
11 | unsigned char index; // Current index of buffer
12 | 
13 | void serial_receive(unsigned char value) { // Called when a byte is received
14 |   buffer[index] = value; // Set buffer at index to value
15 | 
16 |   if (++index == 10) { // If buffer is full
17 |     for (int i = 0; i < 10; ++i) { // Loop buffer
18 |       serial_send(buffer[i]); // Send byte
19 |     }
20 | 
21 |     index = 0; // Reset index
22 |   }
23 | }
24 | 


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