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- /*
- * WARNING: be careful changing this code, it is very timing dependent
- */
-
- #ifndef F_CPU
- #define F_CPU 16000000
- #endif
-
- #include <avr/io.h>
- #include <avr/interrupt.h>
- #include <util/delay.h>
- #include <stdbool.h>
- #include "serial.h"
-
- #ifdef USE_SERIAL
-
- #define _delay_sub_us(x) __builtin_avr_delay_cycles(x)
-
- // Serial pulse period in microseconds.
- #define SELECT_SERIAL_SPEED 1
- #if SELECT_SERIAL_SPEED == 0
- // Very High speed
- #define SERIAL_DELAY 4 // micro sec
- #define READ_WRITE_START_ADJUST 30 // cycles
- #define READ_WRITE_WIDTH_ADJUST 10 // cycles
- #elif SELECT_SERIAL_SPEED == 1
- // High speed
- #define SERIAL_DELAY 6 // micro sec
- #define READ_WRITE_START_ADJUST 23 // cycles
- #define READ_WRITE_WIDTH_ADJUST 10 // cycles
- #elif SELECT_SERIAL_SPEED == 2
- // Middle speed
- #define SERIAL_DELAY 12 // micro sec
- #define READ_WRITE_START_ADJUST 25 // cycles
- #define READ_WRITE_WIDTH_ADJUST 10 // cycles
- #elif SELECT_SERIAL_SPEED == 3
- // Low speed
- #define SERIAL_DELAY 24 // micro sec
- #define READ_WRITE_START_ADJUST 25 // cycles
- #define READ_WRITE_WIDTH_ADJUST 10 // cycles
- #elif SELECT_SERIAL_SPEED == 4
- // Very Low speed
- #define SERIAL_DELAY 50 // micro sec
- #define READ_WRITE_START_ADJUST 25 // cycles
- #define READ_WRITE_WIDTH_ADJUST 10 // cycles
- #else
- #error Illegal Serial Speed
- #endif
-
-
- #define SERIAL_DELAY_HALF1 (SERIAL_DELAY/2)
- #define SERIAL_DELAY_HALF2 (SERIAL_DELAY - SERIAL_DELAY/2)
-
- #define SLAVE_INT_WIDTH 1
- #define SLAVE_INT_RESPONSE_TIME SERIAL_DELAY
-
- uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
- uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
-
- #define SLAVE_DATA_CORRUPT (1<<0)
- volatile uint8_t status = 0;
-
- inline static
- void serial_delay(void) {
- _delay_us(SERIAL_DELAY);
- }
-
- inline static
- void serial_delay_half1(void) {
- _delay_us(SERIAL_DELAY_HALF1);
- }
-
- inline static
- void serial_delay_half2(void) {
- _delay_us(SERIAL_DELAY_HALF2);
- }
-
- inline static
- void serial_output(void) {
- SERIAL_PIN_DDR |= SERIAL_PIN_MASK;
- }
-
- // make the serial pin an input with pull-up resistor
- inline static
- void serial_input_with_pullup(void) {
- SERIAL_PIN_DDR &= ~SERIAL_PIN_MASK;
- SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
- }
-
- inline static
- uint8_t serial_read_pin(void) {
- return !!(SERIAL_PIN_INPUT & SERIAL_PIN_MASK);
- }
-
- inline static
- void serial_low(void) {
- SERIAL_PIN_PORT &= ~SERIAL_PIN_MASK;
- }
-
- inline static
- void serial_high(void) {
- SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
- }
-
- void serial_master_init(void) {
- serial_output();
- serial_high();
- }
-
- void serial_slave_init(void) {
- serial_input_with_pullup();
-
- #if SERIAL_PIN_MASK == _BV(PD0)
- // Enable INT0
- EIMSK |= _BV(INT0);
- // Trigger on falling edge of INT0
- EICRA &= ~(_BV(ISC00) | _BV(ISC01));
- #elif SERIAL_PIN_MASK == _BV(PD2)
- // Enable INT2
- EIMSK |= _BV(INT2);
- // Trigger on falling edge of INT2
- EICRA &= ~(_BV(ISC20) | _BV(ISC21));
- #else
- #error unknown SERIAL_PIN_MASK value
- #endif
- }
-
- // Used by the sender to synchronize timing with the reciver.
- static
- void sync_recv(void) {
- for (int i = 0; i < SERIAL_DELAY*5 && serial_read_pin(); i++ ) {
- }
- // This shouldn't hang if the slave disconnects because the
- // serial line will float to high if the slave does disconnect.
- while (!serial_read_pin());
- }
-
- // Used by the reciver to send a synchronization signal to the sender.
- static
- void sync_send(void) {
- serial_low();
- serial_delay();
- serial_high();
- }
-
- // Reads a byte from the serial line
- static
- uint8_t serial_read_byte(void) {
- uint8_t byte = 0;
- _delay_sub_us(READ_WRITE_START_ADJUST);
- for ( uint8_t i = 0; i < 8; ++i) {
- serial_delay_half1(); // read the middle of pulses
- byte = (byte << 1) | serial_read_pin();
- _delay_sub_us(READ_WRITE_WIDTH_ADJUST);
- serial_delay_half2();
- }
- return byte;
- }
-
- // Sends a byte with MSB ordering
- static
- void serial_write_byte(uint8_t data) {
- uint8_t b = 1<<7;
- while( b ) {
- if(data & b) {
- serial_high();
- } else {
- serial_low();
- }
- b >>= 1;
- serial_delay();
- }
- serial_low(); // sync_send() / senc_recv() need raise edge
- }
-
- // interrupt handle to be used by the slave device
- ISR(SERIAL_PIN_INTERRUPT) {
- serial_output();
-
- // slave send phase
- uint8_t checksum = 0;
- for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
- sync_send();
- serial_write_byte(serial_slave_buffer[i]);
- checksum += serial_slave_buffer[i];
- }
- sync_send();
- serial_write_byte(checksum);
-
- // slave switch to input
- sync_send(); //0
- serial_delay_half1(); //1
- serial_low(); //2
- serial_input_with_pullup(); //2
- serial_delay_half1(); //3
-
- // slave recive phase
- uint8_t checksum_computed = 0;
- for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
- sync_recv();
- serial_master_buffer[i] = serial_read_byte();
- checksum_computed += serial_master_buffer[i];
- }
- sync_recv();
- uint8_t checksum_received = serial_read_byte();
-
- if ( checksum_computed != checksum_received ) {
- status |= SLAVE_DATA_CORRUPT;
- } else {
- status &= ~SLAVE_DATA_CORRUPT;
- }
-
- sync_recv(); //weit master output to high
- }
-
- inline
- bool serial_slave_DATA_CORRUPT(void) {
- return status & SLAVE_DATA_CORRUPT;
- }
-
- // Copies the serial_slave_buffer to the master and sends the
- // serial_master_buffer to the slave.
- //
- // Returns:
- // 0 => no error
- // 1 => slave did not respond
- // 2 => checksum error
- int serial_update_buffers(void) {
- // this code is very time dependent, so we need to disable interrupts
- cli();
-
- // signal to the slave that we want to start a transaction
- serial_output();
- serial_low();
- _delay_us(SLAVE_INT_WIDTH);
-
- // wait for the slaves response
- serial_input_with_pullup();
- _delay_us(SLAVE_INT_RESPONSE_TIME);
-
- // check if the slave is present
- if (serial_read_pin()) {
- // slave failed to pull the line low, assume not present
- serial_output();
- serial_high();
- sei();
- return 1;
- }
-
- // master recive phase
- // if the slave is present syncronize with it
-
- uint8_t checksum_computed = 0;
- // receive data from the slave
- for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
- sync_recv();
- serial_slave_buffer[i] = serial_read_byte();
- checksum_computed += serial_slave_buffer[i];
- }
- sync_recv();
- uint8_t checksum_received = serial_read_byte();
-
- if (checksum_computed != checksum_received) {
- serial_output();
- serial_high();
- sei();
- return 2;
- }
-
- // master switch to output
- sync_recv(); //0
- serial_delay(); //1
- serial_low(); //3
- serial_output(); // 3
- serial_delay_half1(); //4
-
- // master send phase
- uint8_t checksum = 0;
-
- for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
- sync_send();
- serial_write_byte(serial_master_buffer[i]);
- checksum += serial_master_buffer[i];
- }
- sync_send();
- serial_write_byte(checksum);
-
- // always, release the line when not in use
- sync_send();
-
- sei();
- return 0;
- }
-
- #endif
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