2 * WARNING: be careful changing this code, it is very timing dependent
10 #include <avr/interrupt.h>
11 #include <util/delay.h>
17 #define _delay_sub_us(x) __builtin_avr_delay_cycles(x)
19 // Serial pulse period in microseconds.
20 #define SELECT_SERIAL_SPEED 1
21 #if SELECT_SERIAL_SPEED == 0
23 #define SERIAL_DELAY 4 // micro sec
24 #define READ_WRITE_START_ADJUST 30 // cycles
25 #define READ_WRITE_WIDTH_ADJUST 10 // cycles
26 #elif SELECT_SERIAL_SPEED == 1
28 #define SERIAL_DELAY 6 // micro sec
29 #define READ_WRITE_START_ADJUST 23 // cycles
30 #define READ_WRITE_WIDTH_ADJUST 10 // cycles
31 #elif SELECT_SERIAL_SPEED == 2
33 #define SERIAL_DELAY 12 // micro sec
34 #define READ_WRITE_START_ADJUST 25 // cycles
35 #define READ_WRITE_WIDTH_ADJUST 10 // cycles
36 #elif SELECT_SERIAL_SPEED == 3
38 #define SERIAL_DELAY 24 // micro sec
39 #define READ_WRITE_START_ADJUST 25 // cycles
40 #define READ_WRITE_WIDTH_ADJUST 10 // cycles
41 #elif SELECT_SERIAL_SPEED == 4
43 #define SERIAL_DELAY 50 // micro sec
44 #define READ_WRITE_START_ADJUST 25 // cycles
45 #define READ_WRITE_WIDTH_ADJUST 10 // cycles
47 #error Illegal Serial Speed
51 #define SERIAL_DELAY_HALF1 (SERIAL_DELAY/2)
52 #define SERIAL_DELAY_HALF2 (SERIAL_DELAY - SERIAL_DELAY/2)
54 #define SLAVE_INT_WIDTH 1
55 #define SLAVE_INT_RESPONSE_TIME SERIAL_DELAY
57 uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
58 uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
60 #define SLAVE_DATA_CORRUPT (1<<0)
61 volatile uint8_t status = 0;
64 void serial_delay(void) {
65 _delay_us(SERIAL_DELAY);
69 void serial_delay_half1(void) {
70 _delay_us(SERIAL_DELAY_HALF1);
74 void serial_delay_half2(void) {
75 _delay_us(SERIAL_DELAY_HALF2);
79 void serial_output(void) {
80 SERIAL_PIN_DDR |= SERIAL_PIN_MASK;
83 // make the serial pin an input with pull-up resistor
85 void serial_input_with_pullup(void) {
86 SERIAL_PIN_DDR &= ~SERIAL_PIN_MASK;
87 SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
91 uint8_t serial_read_pin(void) {
92 return !!(SERIAL_PIN_INPUT & SERIAL_PIN_MASK);
96 void serial_low(void) {
97 SERIAL_PIN_PORT &= ~SERIAL_PIN_MASK;
101 void serial_high(void) {
102 SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
105 void serial_master_init(void) {
110 void serial_slave_init(void) {
111 serial_input_with_pullup();
113 #ifndef USE_SERIAL_PD2
116 // Trigger on falling edge of INT0
117 EICRA &= ~(_BV(ISC00) | _BV(ISC01));
121 // Trigger on falling edge of INT2
122 EICRA &= ~(_BV(ISC20) | _BV(ISC21));
126 // Used by the sender to synchronize timing with the reciver.
128 void sync_recv(void) {
129 for (int i = 0; i < SERIAL_DELAY*5 && serial_read_pin(); i++ ) {
131 // This shouldn't hang if the slave disconnects because the
132 // serial line will float to high if the slave does disconnect.
133 while (!serial_read_pin());
136 // Used by the reciver to send a synchronization signal to the sender.
138 void sync_send(void) {
144 // Reads a byte from the serial line
146 uint8_t serial_read_byte(void) {
148 _delay_sub_us(READ_WRITE_START_ADJUST);
149 for ( uint8_t i = 0; i < 8; ++i) {
150 serial_delay_half1(); // read the middle of pulses
151 byte = (byte << 1) | serial_read_pin();
152 _delay_sub_us(READ_WRITE_WIDTH_ADJUST);
153 serial_delay_half2();
158 // Sends a byte with MSB ordering
160 void serial_write_byte(uint8_t data) {
171 serial_low(); // sync_send() / senc_recv() need raise edge
174 // interrupt handle to be used by the slave device
175 ISR(SERIAL_PIN_INTERRUPT) {
179 uint8_t checksum = 0;
180 for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
182 serial_write_byte(serial_slave_buffer[i]);
183 checksum += serial_slave_buffer[i];
186 serial_write_byte(checksum);
188 // slave switch to input
190 serial_delay_half1(); //1
192 serial_input_with_pullup(); //2
193 serial_delay_half1(); //3
195 // slave recive phase
196 uint8_t checksum_computed = 0;
197 for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
199 serial_master_buffer[i] = serial_read_byte();
200 checksum_computed += serial_master_buffer[i];
203 uint8_t checksum_received = serial_read_byte();
205 if ( checksum_computed != checksum_received ) {
206 status |= SLAVE_DATA_CORRUPT;
208 status &= ~SLAVE_DATA_CORRUPT;
211 sync_recv(); //weit master output to high
215 bool serial_slave_DATA_CORRUPT(void) {
216 return status & SLAVE_DATA_CORRUPT;
219 // Copies the serial_slave_buffer to the master and sends the
220 // serial_master_buffer to the slave.
224 // 1 => slave did not respond
225 // 2 => checksum error
226 int serial_update_buffers(void) {
227 // this code is very time dependent, so we need to disable interrupts
230 // signal to the slave that we want to start a transaction
233 _delay_us(SLAVE_INT_WIDTH);
235 // wait for the slaves response
236 serial_input_with_pullup();
237 _delay_us(SLAVE_INT_RESPONSE_TIME);
239 // check if the slave is present
240 if (serial_read_pin()) {
241 // slave failed to pull the line low, assume not present
248 // master recive phase
249 // if the slave is present syncronize with it
251 uint8_t checksum_computed = 0;
252 // receive data from the slave
253 for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
255 serial_slave_buffer[i] = serial_read_byte();
256 checksum_computed += serial_slave_buffer[i];
259 uint8_t checksum_received = serial_read_byte();
261 if (checksum_computed != checksum_received) {
268 // master switch to output
272 serial_output(); // 3
273 serial_delay_half1(); //4
276 uint8_t checksum = 0;
278 for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
280 serial_write_byte(serial_master_buffer[i]);
281 checksum += serial_master_buffer[i];
284 serial_write_byte(checksum);
286 // always, release the line when not in use