diff --git a/src/stm32/Kconfig b/src/stm32/Kconfig
index 9eef1430..e9f086a0 100644
--- a/src/stm32/Kconfig
+++ b/src/stm32/Kconfig
@@ -7,6 +7,7 @@ config STM32_SELECT
     default y
     select HAVE_GPIO
     select HAVE_GPIO_ADC
+    select HAVE_GPIO_I2C
     select HAVE_GPIO_SPI
     select HAVE_GPIO_BITBANGING
 
diff --git a/src/stm32/Makefile b/src/stm32/Makefile
index ecc3999f..f7df2a4d 100644
--- a/src/stm32/Makefile
+++ b/src/stm32/Makefile
@@ -25,6 +25,7 @@ src-$(CONFIG_MACH_STM32F1) += stm32/stm32f1.c
 src-$(CONFIG_MACH_STM32F4) += ../lib/stm32f4/system_stm32f4xx.c
 src-$(CONFIG_MACH_STM32F4) += stm32/stm32f4.c
 src-$(CONFIG_HAVE_GPIO_ADC) += stm32/adc.c
+src-$(CONFIG_HAVE_GPIO_I2C) += stm32/i2c.c
 src-$(CONFIG_HAVE_GPIO_SPI) += stm32/spi.c
 usb-src-$(CONFIG_HAVE_STM32_USBFS) := stm32/usbfs.c
 usb-src-$(CONFIG_HAVE_STM32_USBOTG) := stm32/usbotg.c
diff --git a/src/stm32/gpio.h b/src/stm32/gpio.h
index ad8a9979..0fe17596 100644
--- a/src/stm32/gpio.h
+++ b/src/stm32/gpio.h
@@ -39,4 +39,14 @@ void spi_prepare(struct spi_config config);
 void spi_transfer(struct spi_config config, uint8_t receive_data
                   , uint8_t len, uint8_t *data);
 
+struct i2c_config {
+    void *i2c;
+    uint8_t addr;
+};
+
+struct i2c_config i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr);
+void i2c_write(struct i2c_config config, uint8_t write_len, uint8_t *write);
+void i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg
+              , uint8_t read_len, uint8_t *read);
+
 #endif // gpio.h
diff --git a/src/stm32/i2c.c b/src/stm32/i2c.c
new file mode 100644
index 00000000..d4ab6a46
--- /dev/null
+++ b/src/stm32/i2c.c
@@ -0,0 +1,126 @@
+// I2C functions on stm32
+//
+// Copyright (C) 2019  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "autoconf.h" // CONFIG_MACH_STM32F1
+#include "board/misc.h" // timer_is_before
+#include "command.h" // shutdown
+#include "gpio.h" // i2c_setup
+#include "internal.h" // GPIO
+#include "sched.h" // sched_shutdown
+
+struct i2c_info {
+    I2C_TypeDef *i2c;
+    uint8_t scl_pin, sda_pin;
+};
+
+DECL_ENUMERATION_RANGE("i2c_bus", "i2c1", 0, 2);
+DECL_CONSTANT_STR("BUS_PINS_i2c1", "PB6,PB7");
+DECL_CONSTANT_STR("BUS_PINS_i2c2", "PB10,PB11");
+
+static const struct i2c_info i2c_bus[] = {
+    { I2C1, GPIO('B', 6), GPIO('B', 7) },
+    { I2C2, GPIO('B', 10), GPIO('B', 11) },
+};
+
+// Work around stm32 errata causing busy bit to be stuck
+static void
+i2c_busy_errata(uint8_t scl_pin, uint8_t sda_pin)
+{
+    if (! CONFIG_MACH_STM32F1)
+        return;
+    gpio_peripheral(scl_pin, GPIO_OUTPUT | GPIO_OPEN_DRAIN, 1);
+    gpio_peripheral(sda_pin, GPIO_OUTPUT | GPIO_OPEN_DRAIN, 1);
+    gpio_peripheral(sda_pin, GPIO_OUTPUT | GPIO_OPEN_DRAIN, -1);
+    gpio_peripheral(scl_pin, GPIO_OUTPUT | GPIO_OPEN_DRAIN, -1);
+    gpio_peripheral(scl_pin, GPIO_OUTPUT | GPIO_OPEN_DRAIN, 1);
+    gpio_peripheral(sda_pin, GPIO_OUTPUT | GPIO_OPEN_DRAIN, 1);
+}
+
+struct i2c_config
+i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr)
+{
+    // Lookup requested i2c bus
+    if (bus >= ARRAY_SIZE(i2c_bus))
+        shutdown("Unsupported i2c bus");
+    const struct i2c_info *ii = &i2c_bus[bus];
+    I2C_TypeDef *i2c = ii->i2c;
+
+    if (!is_enabled_pclock((uint32_t)i2c)) {
+        // Enable i2c clock and gpio
+        enable_pclock((uint32_t)i2c);
+        i2c_busy_errata(ii->scl_pin, ii->sda_pin);
+        gpio_peripheral(ii->scl_pin, GPIO_FUNCTION(4) | GPIO_OPEN_DRAIN, 1);
+        gpio_peripheral(ii->sda_pin, GPIO_FUNCTION(4) | GPIO_OPEN_DRAIN, 1);
+        i2c->CR1 = I2C_CR1_SWRST;
+        i2c->CR1 = 0;
+
+        // Set 100Khz frequency and enable
+        uint32_t pclk = get_pclock_frequency((uint32_t)i2c);
+        i2c->CR2 = pclk / 1000000;
+        i2c->CCR = pclk / 100000 / 2;
+        i2c->TRISE = (pclk / 1000000) + 1;
+        i2c->CR1 = I2C_CR1_PE;
+    }
+
+    return (struct i2c_config){ .i2c=i2c, .addr=addr<<1 };
+}
+
+static uint32_t
+i2c_wait(I2C_TypeDef *i2c, uint32_t set, uint32_t clear, uint32_t timeout)
+{
+    for (;;) {
+        uint32_t sr1 = i2c->SR1;
+        if ((sr1 & set) == set && (sr1 & clear) == 0)
+            return sr1;
+        if (!timer_is_before(timer_read_time(), timeout))
+            shutdown("i2c timeout");
+    }
+}
+
+static void
+i2c_start(I2C_TypeDef *i2c, uint8_t addr, uint32_t timeout)
+{
+    i2c->CR1 = I2C_CR1_START | I2C_CR1_PE;
+    i2c_wait(i2c, I2C_SR1_SB, 0, timeout);
+    i2c->DR = addr;
+    i2c_wait(i2c, I2C_SR1_ADDR, 0, timeout);
+    uint32_t sr2 = i2c->SR2;
+    if (!(sr2 & I2C_SR2_MSL))
+        shutdown("Failed to send i2c addr");
+}
+
+static void
+i2c_send_byte(I2C_TypeDef *i2c, uint8_t b, uint32_t timeout)
+{
+    i2c->DR = b;
+    i2c_wait(i2c, I2C_SR1_TXE, 0, timeout);
+}
+
+static void
+i2c_stop(I2C_TypeDef *i2c, uint32_t timeout)
+{
+    i2c->CR1 = I2C_CR1_STOP | I2C_CR1_PE;
+    i2c_wait(i2c, 0, I2C_SR1_TXE, timeout);
+}
+
+void
+i2c_write(struct i2c_config config, uint8_t write_len, uint8_t *write)
+{
+    I2C_TypeDef *i2c = config.i2c;
+    uint32_t timeout = timer_read_time() + timer_from_us(5000);
+
+    i2c_start(i2c, config.addr, timeout);
+    while (write_len--)
+        i2c_send_byte(i2c, *write++, timeout);
+    i2c_stop(i2c, timeout);
+}
+
+void
+i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg
+         , uint8_t read_len, uint8_t *read)
+{
+    shutdown("i2c_read not supported on stm32");
+}