I2C read example implemented for RTC IC

lib/rtc_ds1307.c

@@ -0,0 +1,104 @@
+/* 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;
+}

lib/rtc_ds1307.h

@@ -0,0 +1,23 @@
+/* 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) */
+#pragma once
+
+/* setup communication with RTC IC */
+void rtc_setup(void);
+/* read seconds (0-59) from RTC IC */
+uint8_t rtc_read_seconds(void);