--- /dev/null
+/*
+ * 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
projects / qmk_firmware.git / blobdiff