/* * WARNING: be careful changing this code, it is very timing dependent */ #ifndef F_CPU #define F_CPU 16000000 #endif #include #include #include #include #include "serial.h" #ifndef USE_I2C // Serial pulse period in microseconds. Its probably a bad idea to lower this // value. #define SERIAL_DELAY 24 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_output(void) { SERIAL_PIN_DDR |= SERIAL_PIN_MASK; } // make the serial pin an input with pull-up resistor inline static void serial_input(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(); // Enable INT0 EIMSK |= _BV(INT0); // Trigger on falling edge of INT0 EICRA &= ~(_BV(ISC00) | _BV(ISC01)); } // Used by the master to synchronize timing with the slave. static void sync_recv(void) { serial_input(); // 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()); serial_delay(); } // Used by the slave to send a synchronization signal to the master. static void sync_send(void) { serial_output(); serial_low(); serial_delay(); serial_high(); } // Reads a byte from the serial line static uint8_t serial_read_byte(void) { uint8_t byte = 0; serial_input(); for ( uint8_t i = 0; i < 8; ++i) { byte = (byte << 1) | serial_read_pin(); serial_delay(); _delay_us(1); } return byte; } // Sends a byte with MSB ordering static void serial_write_byte(uint8_t data) { uint8_t b = 8; serial_output(); while( b-- ) { if(data & (1 << b)) { serial_high(); } else { serial_low(); } serial_delay(); } } // interrupt handle to be used by the slave device ISR(SERIAL_PIN_INTERRUPT) { sync_send(); uint8_t checksum = 0; for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) { serial_write_byte(serial_slave_buffer[i]); sync_send(); checksum += serial_slave_buffer[i]; } serial_write_byte(checksum); sync_send(); // wait for the sync to finish sending serial_delay(); // read the middle of pulses _delay_us(SERIAL_DELAY/2); uint8_t checksum_computed = 0; for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) { serial_master_buffer[i] = serial_read_byte(); sync_send(); checksum_computed += serial_master_buffer[i]; } uint8_t checksum_received = serial_read_byte(); sync_send(); serial_input(); // end transaction if ( checksum_computed != checksum_received ) { status |= SLAVE_DATA_CORRUPT; } else { status &= ~SLAVE_DATA_CORRUPT; } } 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 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(1); // wait for the slaves response serial_input(); serial_high(); _delay_us(SERIAL_DELAY); // check if the slave is present if (serial_read_pin()) { // slave failed to pull the line low, assume not present sei(); return 1; } // if the slave is present syncronize with it sync_recv(); uint8_t checksum_computed = 0; // 
The files in this project are licensed under the MIT license
It uses the following libraries
uGFX - with it's own license, see the license.html file in the uGFX subfolder for more information
tmk_core - is indirectly used and not included in the repository. It's licensed under the GPLv2 license
Chibios - which is used by tmk_core is licensed under GPLv3.

Therefore the effective license for any project using the library is GPLv3

The MIT License (MIT)

Copyright (c) 2016 Fred Sundvik

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of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
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SOFTWARE.
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