diff --git a/ports/stm32/i2cslave.c b/ports/stm32/i2cslave.c
new file mode 100644
index 0000000000..f8ff19cd6c
--- /dev/null
+++ b/ports/stm32/i2cslave.c
@@ -0,0 +1,101 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "i2cslave.h"
+
+#if defined(STM32F4)
+
+void i2c_slave_init_helper(i2c_slave_t *i2c, int addr) {
+    i2c->CR2 = I2C_CR2_ITBUFEN | I2C_CR2_ITEVTEN | 4 << I2C_CR2_FREQ_Pos;
+    i2c->OAR1 = 1 << 14 | addr << 1;
+    i2c->OAR2 = 0;
+    i2c->CR1 = I2C_CR1_ACK | I2C_CR1_PE;
+}
+
+void i2c_slave_ev_irq_handler(i2c_slave_t *i2c) {
+    uint32_t sr1 = i2c->SR1;
+    if (sr1 & I2C_SR1_ADDR) {
+        // Address matched
+        // Read of SR1, SR2 needed to clear ADDR bit
+        sr1 = i2c->SR1;
+        uint32_t sr2 = i2c->SR2;
+        i2c_slave_process_addr_match((sr2 >> I2C_SR2_TRA_Pos) & 1);
+    }
+    if (sr1 & I2C_SR1_STOPF) {
+        // STOPF only set at end of RX mode (in TX mode AF is set on NACK)
+        // Read of SR1, write CR1 needed to clear STOPF bit
+        sr1 = i2c->SR1;
+        i2c->CR1 &= ~I2C_CR1_ACK;
+        i2c_slave_process_rx_end();
+        i2c->CR1 |= I2C_CR1_ACK;
+    }
+    if (sr1 & I2C_SR1_TXE) {
+        i2c->DR = i2c_slave_process_tx_byte();
+    }
+    if (sr1 & I2C_SR1_RXNE) {
+        i2c_slave_process_rx_byte(i2c->DR);
+    }
+}
+
+#elif defined(STM32F7)
+
+void i2c_slave_init_helper(i2c_slave_t *i2c, int addr) {
+    i2c->CR1 = I2C_CR1_STOPIE | I2C_CR1_ADDRIE | I2C_CR1_RXIE | I2C_CR1_TXIE;
+    i2c->CR2 = 0;
+    i2c->OAR1 = I2C_OAR1_OA1EN | addr << 1;
+    i2c->OAR2 = 0;
+    i2c->CR1 |= I2C_CR1_PE;
+}
+
+void i2c_slave_ev_irq_handler(i2c_slave_t *i2c) {
+    uint32_t isr = i2c->ISR;
+    if (isr & I2C_ISR_ADDR) {
+        // Address matched
+        // Set TXE so that TXDR is flushed and ready for the first byte
+        i2c->ISR = I2C_ISR_TXE;
+        i2c->ICR = I2C_ICR_ADDRCF;
+        i2c_slave_process_addr_match(0);
+    }
+    if (isr & I2C_ISR_STOPF) {
+        // STOPF only set for STOP condition, not a repeated START
+        i2c->ICR = I2C_ICR_STOPCF;
+        i2c->OAR1 &= ~I2C_OAR1_OA1EN;
+        if (i2c->ISR & I2C_ISR_DIR) {
+            //i2c_slave_process_tx_end();
+        } else {
+            i2c_slave_process_rx_end();
+        }
+        i2c->OAR1 |= I2C_OAR1_OA1EN;
+    }
+    if (isr & I2C_ISR_TXIS) {
+        i2c->TXDR = i2c_slave_process_tx_byte();
+    }
+    if (isr & I2C_ISR_RXNE) {
+        i2c_slave_process_rx_byte(i2c->RXDR);
+    }
+}
+
+#endif
diff --git a/ports/stm32/i2cslave.h b/ports/stm32/i2cslave.h
new file mode 100644
index 0000000000..ac35c0cc82
--- /dev/null
+++ b/ports/stm32/i2cslave.h
@@ -0,0 +1,60 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_STM32_I2CSLAVE_H
+#define MICROPY_INCLUDED_STM32_I2CSLAVE_H
+
+#include STM32_HAL_H
+
+typedef I2C_TypeDef i2c_slave_t;
+
+void i2c_slave_init_helper(i2c_slave_t *i2c, int addr);
+
+static inline void i2c_slave_init(i2c_slave_t *i2c, int irqn, int irq_pri, int addr) {
+    int en_bit = RCC_APB1ENR_I2C1EN_Pos + ((uintptr_t)i2c - I2C1_BASE) / (I2C2_BASE - I2C1_BASE);
+    RCC->APB1ENR |= 1 << en_bit;
+    volatile uint32_t tmp = RCC->APB1ENR; // Delay after enabling clock
+    (void)tmp;
+
+    i2c_slave_init_helper(i2c, addr);
+
+    NVIC_SetPriority(irqn, irq_pri);
+    NVIC_EnableIRQ(irqn);
+}
+
+static inline void i2c_slave_shutdown(i2c_slave_t *i2c, int irqn) {
+    i2c->CR1 = 0;
+    NVIC_DisableIRQ(irqn);
+}
+
+void i2c_slave_ev_irq_handler(i2c_slave_t *i2c);
+
+// These should be provided externally
+int i2c_slave_process_addr_match(int rw);
+int i2c_slave_process_rx_byte(uint8_t val);
+void i2c_slave_process_rx_end(void);
+uint8_t i2c_slave_process_tx_byte(void);
+
+#endif // MICROPY_INCLUDED_STM32_I2CSLAVE_H