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diff --git a/circuitpython/shared-module/bitbangio/I2C.c b/circuitpython/shared-module/bitbangio/I2C.c
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+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * SPDX-FileCopyrightText: Copyright (c) 2016 Damien P. George, Scott Shawcroft
+ *
+ * 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 "shared-bindings/bitbangio/I2C.h"
+#include "py/mperrno.h"
+#include "py/obj.h"
+#include "py/runtime.h"
+
+#include "common-hal/microcontroller/Pin.h"
+#include "shared-bindings/microcontroller/__init__.h"
+#include "shared-bindings/digitalio/DigitalInOut.h"
+#include "supervisor/shared/translate.h"
+
+STATIC void delay(bitbangio_i2c_obj_t *self) {
+ // We need to use an accurate delay to get acceptable I2C
+ // speeds (eg 1us should be not much more than 1us).
+ common_hal_mcu_delay_us(self->us_delay);
+}
+
+STATIC void scl_low(bitbangio_i2c_obj_t *self) {
+ common_hal_digitalio_digitalinout_set_value(&self->scl, false);
+}
+
+STATIC void scl_release(bitbangio_i2c_obj_t *self) {
+ common_hal_digitalio_digitalinout_set_value(&self->scl, true);
+ uint32_t count = self->us_timeout;
+ delay(self);
+ // For clock stretching, wait for the SCL pin to be released, with timeout.
+ common_hal_digitalio_digitalinout_switch_to_input(&self->scl, PULL_UP);
+ for (; !common_hal_digitalio_digitalinout_get_value(&self->scl) && count; --count) {
+ common_hal_mcu_delay_us(1);
+ }
+ common_hal_digitalio_digitalinout_switch_to_output(&self->scl, true, DRIVE_MODE_OPEN_DRAIN);
+ // raise exception on timeout
+ if (count == 0) {
+ mp_raise_msg(&mp_type_TimeoutError, translate("Clock stretch too long"));
+ }
+}
+
+STATIC void sda_low(bitbangio_i2c_obj_t *self) {
+ common_hal_digitalio_digitalinout_set_value(&self->sda, false);
+}
+
+STATIC void sda_release(bitbangio_i2c_obj_t *self) {
+ common_hal_digitalio_digitalinout_set_value(&self->sda, true);
+}
+
+STATIC bool sda_read(bitbangio_i2c_obj_t *self) {
+ common_hal_digitalio_digitalinout_switch_to_input(&self->sda, PULL_UP);
+ bool value = common_hal_digitalio_digitalinout_get_value(&self->sda);
+ common_hal_digitalio_digitalinout_switch_to_output(&self->sda, true, DRIVE_MODE_OPEN_DRAIN);
+ return value;
+}
+
+STATIC void start(bitbangio_i2c_obj_t *self) {
+ sda_release(self);
+ delay(self);
+ scl_release(self);
+ sda_low(self);
+ delay(self);
+}
+
+STATIC void stop(bitbangio_i2c_obj_t *self) {
+ delay(self);
+ sda_low(self);
+ delay(self);
+ scl_release(self);
+ sda_release(self);
+ delay(self);
+}
+
+STATIC int write_byte(bitbangio_i2c_obj_t *self, uint8_t val) {
+ delay(self);
+ scl_low(self);
+
+ for (int i = 7; i >= 0; i--) {
+ if ((val >> i) & 1) {
+ sda_release(self);
+ } else {
+ sda_low(self);
+ }
+ delay(self);
+ scl_release(self);
+ scl_low(self);
+ }
+
+ sda_release(self);
+ delay(self);
+ scl_release(self);
+
+ int ret = sda_read(self);
+ delay(self);
+ scl_low(self);
+
+ return !ret;
+}
+
+STATIC bool read_byte(bitbangio_i2c_obj_t *self, uint8_t *val, bool ack) {
+ delay(self);
+ scl_low(self);
+ delay(self);
+
+ uint8_t data = 0;
+ for (int i = 7; i >= 0; i--) {
+ scl_release(self);
+ data = (data << 1) | sda_read(self);
+ scl_low(self);
+ delay(self);
+ }
+ *val = data;
+
+ // send ack/nack bit
+ if (ack) {
+ sda_low(self);
+ }
+ delay(self);
+ scl_release(self);
+ scl_low(self);
+ sda_release(self);
+
+ return true;
+}
+
+void shared_module_bitbangio_i2c_construct(bitbangio_i2c_obj_t *self,
+ const mcu_pin_obj_t *scl,
+ const mcu_pin_obj_t *sda,
+ uint32_t frequency,
+ uint32_t us_timeout) {
+
+ self->us_timeout = us_timeout;
+ self->us_delay = 500000 / frequency;
+ if (self->us_delay == 0) {
+ self->us_delay = 1;
+ }
+ digitalinout_result_t result = common_hal_digitalio_digitalinout_construct(&self->scl, scl);
+ if (result != DIGITALINOUT_OK) {
+ return;
+ }
+ result = common_hal_digitalio_digitalinout_construct(&self->sda, sda);
+ if (result != DIGITALINOUT_OK) {
+ common_hal_digitalio_digitalinout_deinit(&self->scl);
+ return;
+ }
+ common_hal_digitalio_digitalinout_switch_to_output(&self->scl, true, DRIVE_MODE_OPEN_DRAIN);
+ common_hal_digitalio_digitalinout_switch_to_output(&self->sda, true, DRIVE_MODE_OPEN_DRAIN);
+
+ stop(self);
+}
+
+bool shared_module_bitbangio_i2c_deinited(bitbangio_i2c_obj_t *self) {
+ // If one is deinited, both will be.
+ return common_hal_digitalio_digitalinout_deinited(&self->scl);
+}
+
+void shared_module_bitbangio_i2c_deinit(bitbangio_i2c_obj_t *self) {
+ if (shared_module_bitbangio_i2c_deinited(self)) {
+ return;
+ }
+ common_hal_digitalio_digitalinout_deinit(&self->scl);
+ common_hal_digitalio_digitalinout_deinit(&self->sda);
+}
+
+bool shared_module_bitbangio_i2c_try_lock(bitbangio_i2c_obj_t *self) {
+ bool success = false;
+ common_hal_mcu_disable_interrupts();
+ if (!self->locked) {
+ self->locked = true;
+ success = true;
+ }
+ common_hal_mcu_enable_interrupts();
+ return success;
+}
+
+bool shared_module_bitbangio_i2c_has_lock(bitbangio_i2c_obj_t *self) {
+ return self->locked;
+}
+
+void shared_module_bitbangio_i2c_unlock(bitbangio_i2c_obj_t *self) {
+ self->locked = false;
+}
+
+bool shared_module_bitbangio_i2c_probe(bitbangio_i2c_obj_t *self, uint8_t addr) {
+ start(self);
+ bool ok = write_byte(self, addr << 1);
+ stop(self);
+ return ok;
+}
+
+uint8_t shared_module_bitbangio_i2c_write(bitbangio_i2c_obj_t *self, uint16_t addr,
+ const uint8_t *data, size_t len, bool transmit_stop_bit) {
+ // start the I2C transaction
+ start(self);
+ uint8_t status = 0;
+ if (!write_byte(self, addr << 1)) {
+ status = MP_ENODEV;
+ }
+
+ if (status == 0) {
+ for (uint32_t i = 0; i < len; i++) {
+ if (!write_byte(self, data[i])) {
+ status = MP_EIO;
+ break;
+ }
+ }
+ }
+
+ if (transmit_stop_bit) {
+ stop(self);
+ }
+ return status;
+}
+
+uint8_t shared_module_bitbangio_i2c_read(bitbangio_i2c_obj_t *self, uint16_t addr,
+ uint8_t *data, size_t len) {
+ // start the I2C transaction
+ start(self);
+ uint8_t status = 0;
+ if (!write_byte(self, (addr << 1) | 1)) {
+ status = MP_ENODEV;
+ }
+
+ if (status == 0) {
+ for (uint32_t i = 0; i < len; i++) {
+ if (!read_byte(self, data + i, i < len - 1)) {
+ status = MP_EIO;
+ break;
+ }
+ }
+ }
+
+ stop(self);
+ return status;
+}
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