testing I2C on the STM32L1 using libopencm3

i2c_test_stm32l1.c

#include <stdio.h>

#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/stm32/usart.h>
#include <libopencm3/stm32/i2c.h>

static void clock_setup(void) {

    rcc_clock_setup_hsi(&rcc_clock_config[2]);  // 16mhz hsi raw

}

static void gpio_setup(void) {

    rcc_periph_clock_enable(RCC_GPIOA);
    gpio_mode_setup(GPIOA, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO5);

}

static void usart_setup(void) {

    rcc_periph_clock_enable(RCC_USART1);

    gpio_mode_setup(GPIOA, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO9);
    gpio_set_af(GPIOA, GPIO_AF7, GPIO9);

    usart_set_baudrate(USART1, 115200);
    usart_set_databits(USART1, 8);
    usart_set_parity(USART1, USART_PARITY_NONE);
    usart_set_stopbits(USART1, USART_CR2_STOPBITS_1);
    usart_set_flow_control(USART1, USART_FLOWCONTROL_NONE);
    usart_set_mode(USART1, USART_MODE_TX);

    usart_enable(USART1);

    setbuf(stdout, NULL);   // optional

}

static void i2c_setup(void) {

    rcc_periph_clock_enable(RCC_I2C1);

    gpio_mode_setup(GPIOB, GPIO_MODE_AF, GPIO_OTYPE_OD, GPIO8 | GPIO9);
    gpio_set_af(GPIOB, GPIO_AF4, GPIO8 | GPIO9);

    i2c_peripheral_disable(I2C1);
    i2c_set_clock_frequency(I2C1, I2C_CR2_FREQ_36MHZ);
    i2c_set_fast_mode(I2C1);
    i2c_set_ccr(I2C1, 0x1e);
    i2c_set_trise(I2C1, 0x0b);
    i2c_peripheral_enable(I2C1);

}

////

int main(void) {

    int i;

    clock_setup();
    gpio_setup();
    usart_setup();
    i2c_setup();

    while (1) {

        // blink the LED
        gpio_set(GPIOA, GPIO5);
        for (i = 0; i < 1000000; i++) {
            __asm__("nop");
        }
        gpio_clear(GPIOA, GPIO5);
        for (i = 0; i < 1000000; i++) {
            __asm__("nop");
        }

        // query an i2c address
        i2c_send_start(I2C1);
        i2c_send_7bit_address(I2C1, 0x18, I2C_WRITE);
        i2c_send_stop(I2C1);

    }

    return 0;

}