/* This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
/* Copyright (c) 2016 King Kévin <kingkevin@cuvoodoo.info> */
/* this library handles communication with the I2C RTC IC Maxim DS1307 */
/* peripherals used: I2C (check source for details) */

/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdio.h> // standard I/O facilities
#include <stdlib.h> // general utilities

/* STM32 (including CM3) libraries */
#include <libopencm3/stm32/rcc.h> // real-time control clock library
#include <libopencm3/stm32/gpio.h> // general purpose input output library
#include <libopencm3/stm32/i2c.h> // I2C library
#include <libopencm3/cm3/nvic.h> // interrupt handler
#include <libopencmsis/core_cm3.h> // Cortex M3 utilities

#include "rtc_ds1307.h" // RTC header and definitions

/* which I2C to use */
#define I2C I2C1
#define I2C_RCC RCC_I2C1
#define I2C_IRQ NVIC_I2C1_IRQ
#define I2C_PORT GPIOB
#define I2C_PIN_SDA GPIO_I2C1_SDA // on PB7
#define I2C_PIN_SCL GPIO_I2C1_SCL // on PB6
#define I2C_ADDR 0b1101000 // DS1307 fixed slave address

/* setup communication with RTC IC */
void rtc_setup(void)
{
	/* enable peripheral */
	rcc_periph_clock_enable(RCC_AFIO); // enable clock for alternate function
	rcc_periph_clock_enable(I2C_RCC); // enable clock for I2C peripheral
	gpio_set_mode(I2C_PORT, GPIO_MODE_OUTPUT_10_MHZ, GPIO_CNF_OUTPUT_ALTFN_OPENDRAIN, I2C_PIN_SDA | I2C_PIN_SCL); // setup I2C pin

	/* configure I2C peripheral (see RM008 26.3.3, I2C master) */
	i2c_reset(I2C); // reset configuration
	i2c_peripheral_disable(I2C); // I2C needs to be disable to be configured
	i2c_set_clock_frequency(I2C, rcc_apb1_frequency/1E6); // configure the peripheral clock to the APB1 freq (where it is connected to)
	i2c_set_standard_mode(I2C); // the DS1307 has a maximum I2C SCL freq if 100 kHz (corresponding to the standard mode)
	i2c_set_ccr(I2C, rcc_apb1_frequency/(100E3*2)); // set Thigh/Tlow to generate frequency of 100 kHz
	i2c_set_trise(I2C, rcc_apb1_frequency/1E6); // max rise time for 100 kHz is 1000 ns (~1 MHz)
	i2c_peripheral_enable(I2C); // enable I2C after configuration completed
}

/* read memory from RTC IC
 * read <len> data into <data>
 * return if read succeeded */
static bool rtc_read_memory(uint8_t* data, size_t len)
{
	bool to_return = false; // return if read succeeded
	if (data==NULL || len==0) { // verify there it data to be read
		goto error;
	}
	i2c_send_start(I2C); // send start condition to start transaction
	while (!(I2C_SR1(I2C) & I2C_SR1_SB)); // wait until start bit is transmitted
	if (!(I2C_SR2(I2C) & I2C_SR2_MSL)) { // verify if in master mode
		goto error;
	}
	i2c_send_7bit_address(I2C, I2C_ADDR, I2C_READ); // transmit address
	while (!(I2C_SR1(I2C) & I2C_SR1_ADDR)); // wait until address is transmitted
	if (I2C_SR2(I2C) & I2C_SR2_TRA) { // verify we are in receive mode (and read SR2 to clear ADDR)
		goto error;
	}
	for (size_t i=0; i<len; i++) { // read bytes
		if (i==len-1) { // prepare to sent NACK for last byte
			i2c_disable_ack(I2C); // NACK received to stop slave transmission
			i2c_send_stop(I2C); // send STOP after receiving byte
		} else {
			i2c_enable_ack(I2C); // ACK received byte to continue slave transmission
		}
		while (!(I2C_SR1(I2C) & I2C_SR1_RxNE)); // wait until byte has been received
		data[i] = i2c_get_data(I2C); // read received byte
	}
	to_return = true;
error:
	if (I2C_SR2(I2C) & I2C_SR2_BUSY) { // release bus if busy
		i2c_send_stop(I2C); // send stop to release bus
	}
	while (I2C_SR2(I2C) & I2C_SR2_MSL); // wait until bus released (non master mode)
	return to_return;
}

/* read seconds (0-59) from RTC IC */
uint8_t rtc_read_seconds(void)
{
	uint8_t to_return = 0; // seconds to return
	rtc_read_memory(&to_return, 1); // read a single byte to test
	return to_return;
}