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qmk_firmware/keyboards/mint60/serial.c

296 lines
6.8 KiB

/*
* 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