2 * WARNING: be careful changing this code, it is very timing dependent
10 #include <avr/interrupt.h>
11 #include <util/delay.h>
17 // Serial pulse period in microseconds. Its probably a bad idea to lower this
19 #define SERIAL_DELAY 24
21 uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
22 uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
24 #define SLAVE_DATA_CORRUPT (1<<0)
25 volatile uint8_t status = 0;
28 void serial_delay(void) {
29 _delay_us(SERIAL_DELAY);
33 void serial_output(void) {
34 SERIAL_PIN_DDR |= SERIAL_PIN_MASK;
37 // make the serial pin an input with pull-up resistor
39 void serial_input(void) {
40 SERIAL_PIN_DDR &= ~SERIAL_PIN_MASK;
41 SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
45 uint8_t serial_read_pin(void) {
46 return !!(SERIAL_PIN_INPUT & SERIAL_PIN_MASK);
50 void serial_low(void) {
51 SERIAL_PIN_PORT &= ~SERIAL_PIN_MASK;
55 void serial_high(void) {
56 SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
59 void serial_master_init(void) {
64 void serial_slave_init(void) {
67 #ifndef USE_SERIAL_PD2
70 // Trigger on falling edge of INT0
71 EICRA &= ~(_BV(ISC00) | _BV(ISC01));
75 // Trigger on falling edge of INT2
76 EICRA &= ~(_BV(ISC20) | _BV(ISC21));
80 // Used by the master to synchronize timing with the slave.
82 void sync_recv(void) {
84 // This shouldn't hang if the slave disconnects because the
85 // serial line will float to high if the slave does disconnect.
86 while (!serial_read_pin());
90 // Used by the slave to send a synchronization signal to the master.
92 void sync_send(void) {
101 // Reads a byte from the serial line
103 uint8_t serial_read_byte(void) {
106 for ( uint8_t i = 0; i < 8; ++i) {
107 byte = (byte << 1) | serial_read_pin();
115 // Sends a byte with MSB ordering
117 void serial_write_byte(uint8_t data) {
121 if(data & (1 << b)) {
130 // interrupt handle to be used by the slave device
131 ISR(SERIAL_PIN_INTERRUPT) {
134 uint8_t checksum = 0;
135 for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
136 serial_write_byte(serial_slave_buffer[i]);
138 checksum += serial_slave_buffer[i];
140 serial_write_byte(checksum);
143 // wait for the sync to finish sending
146 // read the middle of pulses
147 _delay_us(SERIAL_DELAY/2);
149 uint8_t checksum_computed = 0;
150 for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
151 serial_master_buffer[i] = serial_read_byte();
153 checksum_computed += serial_master_buffer[i];
155 uint8_t checksum_received = serial_read_byte();
158 serial_input(); // end transaction
160 if ( checksum_computed != checksum_received ) {
161 status |= SLAVE_DATA_CORRUPT;
163 status &= ~SLAVE_DATA_CORRUPT;
168 bool serial_slave_DATA_CORRUPT(void) {
169 return status & SLAVE_DATA_CORRUPT;
172 // Copies the serial_slave_buffer to the master and sends the
173 // serial_master_buffer to the slave.
177 // 1 => slave did not respond
178 int serial_update_buffers(void) {
179 // this code is very time dependent, so we need to disable interrupts
182 // signal to the slave that we want to start a transaction
187 // wait for the slaves response
190 _delay_us(SERIAL_DELAY);
192 // check if the slave is present
193 if (serial_read_pin()) {
194 // slave failed to pull the line low, assume not present
199 // if the slave is present syncronize with it
202 uint8_t checksum_computed = 0;
203 // receive data from the slave
204 for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
205 serial_slave_buffer[i] = serial_read_byte();
207 checksum_computed += serial_slave_buffer[i];
209 uint8_t checksum_received = serial_read_byte();
212 if (checksum_computed != checksum_received) {
217 uint8_t checksum = 0;
218 // send data to the slave
219 for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
220 serial_write_byte(serial_master_buffer[i]);
222 checksum += serial_master_buffer[i];
224 serial_write_byte(checksum);
227 // always, release the line when not in use