Add baseline HAL I2C support

12 files changed, 982 insertions, 4 deletions

diff --git a/ports/stm32f4/Makefile b/ports/stm32f4/Makefile
index 7f0744443..15fed7bde 100755
--- a/ports/stm32f4/Makefile
+++ b/ports/stm32f4/Makefile
@@ -148,6 +148,7 @@ SRC_STM32 = \
 	stm32f4/STM32F4xx_HAL_Driver/Src/stm32f4xx_ll_usb.c \
 	stm32f4/STM32F4xx_HAL_Driver/Src/stm32f4xx_ll_fsmc.c \
 	stm32f4/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_sram.c \
+	stm32f4/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_i2c.c \
 	stm32f4/STM32F4xx_HAL_Driver/Src/stm32f4xx_ll_i2c.c \
 	stm32f4/STM32F4xx_HAL_Driver/Src/stm32f4xx_ll_dma.c \
 	stm32f4/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_i2s.c \
diff --git a/ports/stm32f4/boards/stm32f411re_discovery/mpconfigboard.mk b/ports/stm32f4/boards/stm32f411re_discovery/mpconfigboard.mk
index 7b865b57e..0d15aab49 100644
--- a/ports/stm32f4/boards/stm32f411re_discovery/mpconfigboard.mk
+++ b/ports/stm32f4/boards/stm32f411re_discovery/mpconfigboard.mk
@@ -9,5 +9,4 @@ MCU_SUB_VARIANT = stm32f411xe
 CMSIS_MCU = STM32F411xE
 LD_FILE = boards/STM32F411VETx_FLASH.ld
 TEXT0_ADDR = 0x08000000
-TEXT1_ADDR = 0x08020000
-
+TEXT1_ADDR = 0x08020000
\ No newline at end of file
diff --git a/ports/stm32f4/boards/stm32f412zg_discovery/stm32f4xx_hal_msp.c b/ports/stm32f4/boards/stm32f412zg_discovery/stm32f4xx_hal_msp.c
index 9d29f3607..54f444a71 100644
--- a/ports/stm32f4/boards/stm32f412zg_discovery/stm32f4xx_hal_msp.c
+++ b/ports/stm32f4/boards/stm32f412zg_discovery/stm32f4xx_hal_msp.c
@@ -273,14 +273,14 @@ void HAL_I2C_MspInit(I2C_HandleTypeDef* hi2c)
     */
     GPIO_InitStruct.Pin = I2C2_SCL_Pin;
     GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
-    GPIO_InitStruct.Pull = GPIO_PULLUP;
+    GPIO_InitStruct.Pull = GPIO_NOPULL;//GPIO_PULLUP;
     GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
     GPIO_InitStruct.Alternate = GPIO_AF4_I2C2;
     HAL_GPIO_Init(I2C2_SCL_GPIO_Port, &GPIO_InitStruct);
 
     GPIO_InitStruct.Pin = I2C2_SDA_Pin;
     GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
-    GPIO_InitStruct.Pull = GPIO_PULLUP;
+    GPIO_InitStruct.Pull = GPIO_NOPULL;//GPIO_PULLUP;
     GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
     GPIO_InitStruct.Alternate = GPIO_AF9_I2C2;
     HAL_GPIO_Init(I2C2_SDA_GPIO_Port, &GPIO_InitStruct);
diff --git a/ports/stm32f4/common-hal/busio/I2C.c b/ports/stm32f4/common-hal/busio/I2C.c
new file mode 100644
index 000000000..8e1e57c36
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/I2C.c
@@ -0,0 +1,115 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 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/busio/I2C.h"
+#include "py/mperrno.h"
+#include "py/runtime.h"
+#include "stm32f4xx_hal.h"
+
+#include "shared-bindings/microcontroller/__init__.h"
+#include "supervisor/shared/translate.h"
+
+I2C_HandleTypeDef hi2c2;
+
+void common_hal_busio_i2c_construct(busio_i2c_obj_t *self,
+        const mcu_pin_obj_t* scl, const mcu_pin_obj_t* sda, uint32_t frequency, uint32_t timeout) {
+    hi2c2.Instance = I2C2;
+    hi2c2.Init.ClockSpeed = 100000;
+    hi2c2.Init.DutyCycle = I2C_DUTYCYCLE_2;
+    hi2c2.Init.OwnAddress1 = 0;
+    hi2c2.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
+    hi2c2.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
+    hi2c2.Init.OwnAddress2 = 0;
+    hi2c2.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
+    hi2c2.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
+    if(HAL_I2C_Init(&hi2c2) != HAL_OK) {
+        mp_raise_RuntimeError(translate("I2C Init Error"));
+    } else {
+        mp_printf(&mp_plat_print, "I2C INIT OK");
+    }
+
+    self->sda_pin = sda->number;
+    self->scl_pin = scl->number;
+
+    claim_pin(sda);
+    claim_pin(scl);
+}
+
+bool common_hal_busio_i2c_deinited(busio_i2c_obj_t *self) {
+    return self->sda_pin == NO_PIN;
+}
+
+void common_hal_busio_i2c_deinit(busio_i2c_obj_t *self) {
+    if (common_hal_busio_i2c_deinited(self)) {
+        return;
+    }
+
+    HAL_I2C_MspDeInit(&hi2c2);
+
+    self->sda_pin = NO_PIN;
+    self->scl_pin = NO_PIN;
+}
+
+bool common_hal_busio_i2c_probe(busio_i2c_obj_t *self, uint8_t addr) {
+    return HAL_I2C_IsDeviceReady(&hi2c2, (uint16_t)(addr<<1),2,2) == HAL_OK;
+}
+
+bool common_hal_busio_i2c_try_lock(busio_i2c_obj_t *self) {
+    bool grabbed_lock = false;
+
+    //Critical section code that may be required at some point. 
+    // uint32_t store_primask = __get_PRIMASK();
+    // __disable_irq();
+    // __DMB();
+
+        if (!self->has_lock) {
+            grabbed_lock = true;
+            self->has_lock = true;
+        }
+
+    // __DMB();
+    // __set_PRIMASK(store_primask);
+
+    return grabbed_lock;
+}
+
+bool common_hal_busio_i2c_has_lock(busio_i2c_obj_t *self) {
+    return self->has_lock;
+}
+
+void common_hal_busio_i2c_unlock(busio_i2c_obj_t *self) {
+    self->has_lock = false;
+}
+
+uint8_t common_hal_busio_i2c_write(busio_i2c_obj_t *self, uint16_t addr,
+                                   const uint8_t *data, size_t len, bool transmit_stop_bit) {
+    return HAL_I2C_Master_Transmit(&hi2c2, (uint16_t)(addr<<1), (uint8_t *)data, (uint16_t)len, 2) == HAL_OK ? 0 : MP_EIO;
+}
+
+uint8_t common_hal_busio_i2c_read(busio_i2c_obj_t *self, uint16_t addr,
+        uint8_t *data, size_t len) {
+    return HAL_I2C_Master_Receive(&hi2c2, (uint16_t)(addr<<1), data, (uint16_t)len, 2) == HAL_OK ? 0 : MP_EIO;
+}
diff --git a/ports/stm32f4/common-hal/busio/I2C.h b/ports/stm32f4/common-hal/busio/I2C.h
new file mode 100644
index 000000000..9fe0258a1
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/I2C.h
@@ -0,0 +1,44 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 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.
+ */
+
+#ifndef MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_I2C_H
+#define MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_I2C_H
+
+#include "common-hal/microcontroller/Pin.h"
+
+#include "stm32f4xx_hal.h"
+
+#include "py/obj.h"
+
+typedef struct {
+    mp_obj_base_t base;
+    I2C_HandleTypeDef i2c_handle;
+    bool has_lock;
+    uint8_t scl_pin;
+    uint8_t sda_pin;
+} busio_i2c_obj_t;
+
+#endif // MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_I2C_H
diff --git a/ports/stm32f4/common-hal/busio/OneWire.h b/ports/stm32f4/common-hal/busio/OneWire.h
new file mode 100644
index 000000000..6e8c82979
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/OneWire.h
@@ -0,0 +1,33 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 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.
+ */
+
+#ifndef MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_ONEWIRE_H
+#define MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_ONEWIRE_H
+
+// Use bitbangio.
+#include "shared-module/busio/OneWire.h"
+
+#endif // MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_ONEWIRE_H
diff --git a/ports/stm32f4/common-hal/busio/SPI.c b/ports/stm32f4/common-hal/busio/SPI.c
new file mode 100644
index 000000000..a8b919984
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/SPI.c
@@ -0,0 +1,321 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 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/busio/SPI.h"
+#include "py/mperrno.h"
+#include "py/runtime.h"
+
+#include "boards/board.h"
+#include "common-hal/microcontroller/Pin.h"
+
+void common_hal_busio_spi_construct(busio_spi_obj_t *self,
+         const mcu_pin_obj_t * clock, const mcu_pin_obj_t * mosi,
+         const mcu_pin_obj_t * miso) {
+    // Sercom* sercom = NULL;
+    // uint8_t sercom_index;
+    // uint32_t clock_pinmux = 0;
+    // bool mosi_none = mosi == mp_const_none || mosi == NULL;
+    // bool miso_none = miso == mp_const_none || miso == NULL;
+    // uint32_t mosi_pinmux = 0;
+    // uint32_t miso_pinmux = 0;
+    // uint8_t clock_pad = 0;
+    // uint8_t mosi_pad = 0;
+    // uint8_t miso_pad = 0;
+    // uint8_t dopo = 255;
+
+    // // Special case for SAMR boards.
+    // #ifdef PIN_PC19
+    // if (miso == &pin_PC19) {
+    //     if (mosi == &pin_PB30 && clock == &pin_PC18) {
+    //         sercom = SERCOM4;
+    //         sercom_index = 4;
+    //         clock_pinmux = MUX_F;
+    //         mosi_pinmux = MUX_F;
+    //         miso_pinmux = MUX_F;
+    //         clock_pad = 3;
+    //         mosi_pad = 2;
+    //         miso_pad = 0;
+    //         dopo = samd_peripherals_get_spi_dopo(clock_pad, mosi_pad);
+    //     }
+    //     // Error, leave SERCOM unset to throw an exception later.
+    // } else {
+    // #endif
+    // for (int i = 0; i < NUM_SERCOMS_PER_PIN; i++) {
+    //     sercom_index = clock->sercom[i].index; // 2 for SERCOM2, etc.
+    //     if (sercom_index >= SERCOM_INST_NUM) {
+    //         continue;
+    //     }
+    //     Sercom* potential_sercom = sercom_insts[sercom_index];
+    //     if (
+    //     #if defined(MICROPY_HW_APA102_SCK) && defined(MICROPY_HW_APA102_MOSI) && !defined(CIRCUITPY_BITBANG_APA102)
+    //         (potential_sercom->SPI.CTRLA.bit.ENABLE != 0 &&
+    //          potential_sercom != status_apa102.spi_desc.dev.prvt &&
+    //          !apa102_sck_in_use)) {
+    //     #else
+    //         potential_sercom->SPI.CTRLA.bit.ENABLE != 0) {
+    //     #endif
+    //         continue;
+    //     }
+    //     clock_pinmux = PINMUX(clock->number, (i == 0) ? MUX_C : MUX_D);
+    //     clock_pad = clock->sercom[i].pad;
+    //     if (!samd_peripherals_valid_spi_clock_pad(clock_pad)) {
+    //         continue;
+    //     }
+    //     for (int j = 0; j < NUM_SERCOMS_PER_PIN; j++) {
+    //         if (!mosi_none) {
+    //             if (sercom_index == mosi->sercom[j].index) {
+    //                 mosi_pinmux = PINMUX(mosi->number, (j == 0) ? MUX_C : MUX_D);
+    //                 mosi_pad = mosi->sercom[j].pad;
+    //                 dopo = samd_peripherals_get_spi_dopo(clock_pad, mosi_pad);
+    //                 if (dopo > 0x3) {
+    //                     continue;  // pad combination not possible
+    //                 }
+    //                 if (miso_none) {
+    //                     sercom = potential_sercom;
+    //                     break;
+    //                 }
+    //             } else {
+    //                 continue;
+    //             }
+    //         }
+    //         if (!miso_none) {
+    //             for (int k = 0; k < NUM_SERCOMS_PER_PIN; k++) {
+    //                 if (sercom_index == miso->sercom[k].index) {
+    //                     miso_pinmux = PINMUX(miso->number, (k == 0) ? MUX_C : MUX_D);
+    //                     miso_pad = miso->sercom[k].pad;
+    //                     sercom = potential_sercom;
+    //                     break;
+    //                 }
+    //             }
+    //         }
+    //         if (sercom != NULL) {
+    //             break;
+    //         }
+    //     }
+    //     if (sercom != NULL) {
+    //         break;
+    //     }
+    // }
+    // #ifdef PIN_PC19
+    // }
+    // #endif
+    // if (sercom == NULL) {
+    //     mp_raise_ValueError(translate("Invalid pins"));
+    // }
+
+    // // Set up SPI clocks on SERCOM.
+    // samd_peripherals_sercom_clock_init(sercom, sercom_index);
+
+    // #if defined(MICROPY_HW_APA102_SCK) && defined(MICROPY_HW_APA102_MOSI) && !defined(CIRCUITPY_BITBANG_APA102)
+    // // if we're re-using the dotstar sercom, make sure it is disabled or the init will fail out
+    // hri_sercomspi_clear_CTRLA_ENABLE_bit(sercom);
+    // #endif
+    // if (spi_m_sync_init(&self->spi_desc, sercom) != ERR_NONE) {
+    //     mp_raise_OSError(MP_EIO);
+    // }
+
+    // // Pads must be set after spi_m_sync_init(), which uses default values from
+    // // the prototypical SERCOM.
+    // hri_sercomspi_write_CTRLA_DOPO_bf(sercom, dopo);
+    // hri_sercomspi_write_CTRLA_DIPO_bf(sercom, miso_pad);
+
+    // // Always start at 250khz which is what SD cards need. They are sensitive to
+    // // SPI bus noise before they are put into SPI mode.
+    // uint8_t baud_value = samd_peripherals_spi_baudrate_to_baud_reg_value(250000);
+    // if (spi_m_sync_set_baudrate(&self->spi_desc, baud_value) != ERR_NONE) {
+    //     // spi_m_sync_set_baudrate does not check for validity, just whether the device is
+    //     // busy or not
+    //     mp_raise_OSError(MP_EIO);
+    // }
+
+    // gpio_set_pin_direction(clock->number, GPIO_DIRECTION_OUT);
+    // gpio_set_pin_pull_mode(clock->number, GPIO_PULL_OFF);
+    // gpio_set_pin_function(clock->number, clock_pinmux);
+    // claim_pin(clock);
+    // self->clock_pin = clock->number;
+
+    // if (mosi_none) {
+    //     self->MOSI_pin = NO_PIN;
+    // } else {
+    //     gpio_set_pin_direction(mosi->number, GPIO_DIRECTION_OUT);
+    //     gpio_set_pin_pull_mode(mosi->number, GPIO_PULL_OFF);
+    //     gpio_set_pin_function(mosi->number, mosi_pinmux);
+    //     self->MOSI_pin = mosi->number;
+    //     claim_pin(mosi);
+    // }
+
+    // if (miso_none) {
+    //     self->MISO_pin = NO_PIN;
+    // } else {
+    //     gpio_set_pin_direction(miso->number, GPIO_DIRECTION_IN);
+    //     gpio_set_pin_pull_mode(miso->number, GPIO_PULL_OFF);
+    //     gpio_set_pin_function(miso->number, miso_pinmux);
+    //     self->MISO_pin = miso->number;
+    //     claim_pin(miso);
+    // }
+
+    // spi_m_sync_enable(&self->spi_desc);
+}
+
+void common_hal_busio_spi_never_reset(busio_spi_obj_t *self) {
+    // never_reset_sercom(self->spi_desc.dev.prvt);
+
+    // never_reset_pin_number(self->clock_pin);
+    // never_reset_pin_number(self->MOSI_pin);
+    // never_reset_pin_number(self->MISO_pin);
+}
+
+bool common_hal_busio_spi_deinited(busio_spi_obj_t *self) {
+    //return self->clock_pin == NO_PIN;
+}
+
+void common_hal_busio_spi_deinit(busio_spi_obj_t *self) {
+    // if (common_hal_busio_spi_deinited(self)) {
+    //     return;
+    // }
+    // allow_reset_sercom(self->spi_desc.dev.prvt);
+
+    // spi_m_sync_disable(&self->spi_desc);
+    // spi_m_sync_deinit(&self->spi_desc);
+    // reset_pin_number(self->clock_pin);
+    // reset_pin_number(self->MOSI_pin);
+    // reset_pin_number(self->MISO_pin);
+    // self->clock_pin = NO_PIN;
+}
+
+bool common_hal_busio_spi_configure(busio_spi_obj_t *self,
+         uint32_t baudrate, uint8_t polarity, uint8_t phase, uint8_t bits) {
+    // uint8_t baud_reg_value = samd_peripherals_spi_baudrate_to_baud_reg_value(baudrate);
+
+    // void * hw = self->spi_desc.dev.prvt;
+    // // If the settings are already what we want then don't reset them.
+    // if (hri_sercomspi_get_CTRLA_CPHA_bit(hw) == phase &&
+    //     hri_sercomspi_get_CTRLA_CPOL_bit(hw) == polarity &&
+    //     hri_sercomspi_read_CTRLB_CHSIZE_bf(hw) == ((uint32_t)bits - 8) &&
+    //     hri_sercomspi_read_BAUD_BAUD_bf(hw) == baud_reg_value) {
+    //     return true;
+    // }
+
+    // // Disable, set values (most or all are enable-protected), and re-enable.
+    // spi_m_sync_disable(&self->spi_desc);
+    // hri_sercomspi_wait_for_sync(hw, SERCOM_SPI_SYNCBUSY_MASK);
+
+    // hri_sercomspi_write_CTRLA_CPHA_bit(hw, phase);
+    // hri_sercomspi_write_CTRLA_CPOL_bit(hw, polarity);
+    // hri_sercomspi_write_CTRLB_CHSIZE_bf(hw, bits - 8);
+    // hri_sercomspi_write_BAUD_BAUD_bf(hw, baud_reg_value);
+    // hri_sercomspi_wait_for_sync(hw, SERCOM_SPI_SYNCBUSY_MASK);
+
+    // spi_m_sync_enable(&self->spi_desc);
+    // hri_sercomspi_wait_for_sync(hw, SERCOM_SPI_SYNCBUSY_MASK);
+
+     return true;
+}
+
+bool common_hal_busio_spi_try_lock(busio_spi_obj_t *self) {
+    bool grabbed_lock = false;
+    // CRITICAL_SECTION_ENTER()
+    //     if (!self->has_lock) {
+    //         grabbed_lock = true;
+    //         self->has_lock = true;
+    //     }
+    // CRITICAL_SECTION_LEAVE();
+    return grabbed_lock;
+}
+
+bool common_hal_busio_spi_has_lock(busio_spi_obj_t *self) {
+    return self->has_lock;
+}
+
+void common_hal_busio_spi_unlock(busio_spi_obj_t *self) {
+    self->has_lock = false;
+}
+
+bool common_hal_busio_spi_write(busio_spi_obj_t *self,
+        const uint8_t *data, size_t len) {
+    // if (len == 0) {
+    //     return true;
+    // }
+    // int32_t status;
+    // if (len >= 16) {
+    //     status = sercom_dma_write(self->spi_desc.dev.prvt, data, len);
+    // } else {
+    //     struct io_descriptor *spi_io;
+    //     spi_m_sync_get_io_descriptor(&self->spi_desc, &spi_io);
+    //     status = spi_io->write(spi_io, data, len);
+    // }
+    return 0;//status >= 0; // Status is number of chars read or an error code < 0.
+}
+
+bool common_hal_busio_spi_read(busio_spi_obj_t *self,
+        uint8_t *data, size_t len, uint8_t write_value) {
+    // if (len == 0) {
+    //     return true;
+    // }
+    // int32_t status;
+    // if (len >= 16) {
+    //     status = sercom_dma_read(self->spi_desc.dev.prvt, data, len, write_value);
+    // } else {
+    //     self->spi_desc.dev.dummy_byte = write_value;
+
+    //     struct io_descriptor *spi_io;
+    //     spi_m_sync_get_io_descriptor(&self->spi_desc, &spi_io);
+
+    //     status = spi_io->read(spi_io, data, len);
+    // }
+    return 0;//status >= 0; // Status is number of chars read or an error code < 0.
+}
+
+bool common_hal_busio_spi_transfer(busio_spi_obj_t *self, uint8_t *data_out, uint8_t *data_in, size_t len) {
+    // if (len == 0) {
+    //     return true;
+    // }
+    // int32_t status;
+    // if (len >= 16) {
+    //     status = sercom_dma_transfer(self->spi_desc.dev.prvt, data_out, data_in, len);
+    // } else {
+    //     struct spi_xfer xfer;
+    //     xfer.txbuf = data_out;
+    //     xfer.rxbuf = data_in;
+    //     xfer.size = len;
+    //     status = spi_m_sync_transfer(&self->spi_desc, &xfer);
+    // }
+    return 0;//status >= 0; // Status is number of chars read or an error code < 0.
+}
+
+uint32_t common_hal_busio_spi_get_frequency(busio_spi_obj_t* self) {
+    return 0;//samd_peripherals_spi_baud_reg_value_to_baudrate(hri_sercomspi_read_BAUD_reg(self->spi_desc.dev.prvt));
+}
+
+uint8_t common_hal_busio_spi_get_phase(busio_spi_obj_t* self) {
+    //void * hw = self->spi_desc.dev.prvt;
+    return 0;//hri_sercomspi_get_CTRLA_CPHA_bit(hw);
+}
+
+uint8_t common_hal_busio_spi_get_polarity(busio_spi_obj_t* self) {
+    //void * hw = self->spi_desc.dev.prvt;
+    return 0;//hri_sercomspi_get_CTRLA_CPOL_bit(hw);
+}
diff --git a/ports/stm32f4/common-hal/busio/SPI.h b/ports/stm32f4/common-hal/busio/SPI.h
new file mode 100644
index 000000000..f7ff79b49
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/SPI.h
@@ -0,0 +1,42 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 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.
+ */
+
+#ifndef MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_SPI_H
+#define MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_SPI_H
+
+#include "common-hal/microcontroller/Pin.h"
+
+#include "py/obj.h"
+
+typedef struct {
+    mp_obj_base_t base;
+    bool has_lock;
+    uint8_t clock_pin;
+    uint8_t MOSI_pin;
+    uint8_t MISO_pin;
+} busio_spi_obj_t;
+
+#endif // MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_SPI_H
diff --git a/ports/stm32f4/common-hal/busio/UART.c b/ports/stm32f4/common-hal/busio/UART.c
new file mode 100644
index 000000000..e9a491715
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/UART.c
@@ -0,0 +1,375 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 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 "shared-bindings/microcontroller/__init__.h"
+#include "shared-bindings/busio/UART.h"
+
+#include "mpconfigport.h"
+#include "lib/utils/interrupt_char.h"
+#include "py/gc.h"
+#include "py/mperrno.h"
+#include "py/runtime.h"
+#include "py/stream.h"
+#include "supervisor/shared/translate.h"
+
+#include "tick.h"
+
+void common_hal_busio_uart_construct(busio_uart_obj_t *self,
+        const mcu_pin_obj_t * tx, const mcu_pin_obj_t * rx, uint32_t baudrate,
+        uint8_t bits, uart_parity_t parity, uint8_t stop, mp_float_t timeout,
+        uint8_t receiver_buffer_size) {
+    // Sercom* sercom = NULL;
+    // uint8_t sercom_index = 255; // Unset index
+    // uint32_t rx_pinmux = 0;
+    // uint8_t rx_pad = 255; // Unset pad
+    // uint32_t tx_pinmux = 0;
+    // uint8_t tx_pad = 255; // Unset pad
+
+    // if (bits > 8) {
+    //     mp_raise_NotImplementedError(translate("bytes > 8 bits not supported"));
+    // }
+
+    // bool have_tx = tx != mp_const_none;
+    // bool have_rx = rx != mp_const_none;
+    // if (!have_tx && !have_rx) {
+    //     mp_raise_ValueError(translate("tx and rx cannot both be None"));
+    // }
+
+    // self->baudrate = baudrate;
+    // self->character_bits = bits;
+    // self->timeout_ms = timeout * 1000;
+
+    // // This assignment is only here because the usart_async routines take a *const argument.
+    // struct usart_async_descriptor * const usart_desc_p = (struct usart_async_descriptor * const) &self->usart_desc;
+
+    // for (int i = 0; i < NUM_SERCOMS_PER_PIN; i++) {
+    //     Sercom* potential_sercom = NULL;
+    //     if (have_tx) {
+    //         sercom_index = tx->sercom[i].index;
+    //         if (sercom_index >= SERCOM_INST_NUM) {
+    //             continue;
+    //         }
+    //         potential_sercom = sercom_insts[sercom_index];
+    //         if (potential_sercom->USART.CTRLA.bit.ENABLE != 0 ||
+    //             !(tx->sercom[i].pad == 0 ||
+    //               tx->sercom[i].pad == 2)) {
+    //             continue;
+    //         }
+    //         tx_pinmux = PINMUX(tx->number, (i == 0) ? MUX_C : MUX_D);
+    //         tx_pad = tx->sercom[i].pad;
+    //         if (rx == mp_const_none) {
+    //             sercom = potential_sercom;
+    //             break;
+    //         }
+    //     }
+    //     for (int j = 0; j < NUM_SERCOMS_PER_PIN; j++) {
+    //         if (((!have_tx && rx->sercom[j].index < SERCOM_INST_NUM &&
+    //               sercom_insts[rx->sercom[j].index]->USART.CTRLA.bit.ENABLE == 0) ||
+    //              sercom_index == rx->sercom[j].index) &&
+    //             rx->sercom[j].pad != tx_pad) {
+    //             rx_pinmux = PINMUX(rx->number, (j == 0) ? MUX_C : MUX_D);
+    //             rx_pad = rx->sercom[j].pad;
+    //             sercom = sercom_insts[rx->sercom[j].index];
+    //             sercom_index = rx->sercom[j].index;
+    //             break;
+    //         }
+    //     }
+    //     if (sercom != NULL) {
+    //         break;
+    //     }
+    // }
+    // if (sercom == NULL) {
+    //     mp_raise_ValueError(translate("Invalid pins"));
+    // }
+    // if (!have_tx) {
+    //     tx_pad = 0;
+    //     if (rx_pad == 0) {
+    //         tx_pad = 2;
+    //     }
+    // }
+    // if (!have_rx) {
+    //     rx_pad = (tx_pad + 1) % 4;
+    // }
+
+    // // Set up clocks on SERCOM.
+    // samd_peripherals_sercom_clock_init(sercom, sercom_index);
+
+    // if (rx && receiver_buffer_size > 0) {
+    //     self->buffer_length = receiver_buffer_size;
+    //     // Initially allocate the UART's buffer in the long-lived part of the
+    //     // heap.  UARTs are generally long-lived objects, but the "make long-
+    //     // lived" machinery is incapable of moving internal pointers like
+    //     // self->buffer, so do it manually.  (However, as long as internal
+    //     // pointers like this are NOT moved, allocating the buffer
+    //     // in the long-lived pool is not strictly necessary)
+    //     self->buffer = (uint8_t *) gc_alloc(self->buffer_length * sizeof(uint8_t), false, true);
+    //     if (self->buffer == NULL) {
+    //         common_hal_busio_uart_deinit(self);
+    //         mp_raise_msg(&mp_type_MemoryError, translate("Failed to allocate RX buffer"));
+    //     }
+    // } else {
+    //     self->buffer_length = 0;
+    //     self->buffer = NULL;
+    // }
+
+    // if (usart_async_init(usart_desc_p, sercom, self->buffer, self->buffer_length, NULL) != ERR_NONE) {
+    //     mp_raise_ValueError(translate("Could not initialize UART"));
+    // }
+
+    // // usart_async_init() sets a number of defaults based on a prototypical SERCOM
+    // // which don't necessarily match what we need. After calling it, set the values
+    // // specific to this instantiation of UART.
+
+    // // Set pads computed for this SERCOM.
+    // // TXPO:
+    // // 0x0: TX pad 0; no RTS/CTS
+    // // 0x1: TX pad 2; no RTS/CTS
+    // // 0x2: TX pad 0; RTS: pad 2, CTS: pad 3 (not used by us right now)
+    // // So divide by 2 to map pad to value.
+    // // RXPO:
+    // // 0x0: RX pad 0
+    // // 0x1: RX pad 1
+    // // 0x2: RX pad 2
+    // // 0x3: RX pad 3
+
+    // // Doing a group mask and set of the registers saves 60 bytes over setting the bitfields individually.
+
+    // sercom->USART.CTRLA.reg &= ~(SERCOM_USART_CTRLA_TXPO_Msk |
+    //                              SERCOM_USART_CTRLA_RXPO_Msk |
+    //                              SERCOM_USART_CTRLA_FORM_Msk);
+    // sercom->USART.CTRLA.reg |= SERCOM_USART_CTRLA_TXPO(tx_pad / 2) |
+    //                            SERCOM_USART_CTRLA_RXPO(rx_pad) |
+    //                            (parity == PARITY_NONE ? 0 : SERCOM_USART_CTRLA_FORM(1));
+
+    // // Enable tx and/or rx based on whether the pins were specified.
+    // // CHSIZE is 0 for 8 bits, 5, 6, 7 for 5, 6, 7 bits. 1 for 9 bits, but we don't support that.
+    // sercom->USART.CTRLB.reg &= ~(SERCOM_USART_CTRLB_TXEN |
+    //                              SERCOM_USART_CTRLB_RXEN |
+    //                              SERCOM_USART_CTRLB_PMODE |
+    //                              SERCOM_USART_CTRLB_SBMODE |
+    //                              SERCOM_USART_CTRLB_CHSIZE_Msk);
+    // sercom->USART.CTRLB.reg |= (have_tx ? SERCOM_USART_CTRLB_TXEN : 0) |
+    //                            (have_rx ? SERCOM_USART_CTRLB_RXEN : 0) |
+    //                            (parity == PARITY_ODD ? SERCOM_USART_CTRLB_PMODE : 0) |
+    //                            (stop > 1 ? SERCOM_USART_CTRLB_SBMODE : 0) |
+    //                            SERCOM_USART_CTRLB_CHSIZE(bits % 8);
+
+    // // Set baud rate
+    // common_hal_busio_uart_set_baudrate(self, baudrate);
+
+    // // Turn on rx interrupt handling. The UART async driver has its own set of internal callbacks,
+    // // which are set up by uart_async_init(). These in turn can call user-specified callbacks.
+    // // In fact, the actual interrupts are not enabled unless we set up a user-specified callback.
+    // // This is confusing. It's explained in the Atmel START User Guide -> Implementation Description ->
+    // // Different read function behavior in some asynchronous drivers. As of this writing:
+    // // http://start.atmel.com/static/help/index.html?GUID-79201A5A-226F-4FBB-B0B8-AB0BE0554836
+    // // Look at the ASFv4 code example for async USART.
+    // usart_async_register_callback(usart_desc_p, USART_ASYNC_RXC_CB, usart_async_rxc_callback);
+
+
+    // if (have_tx) {
+    //     gpio_set_pin_direction(tx->number, GPIO_DIRECTION_OUT);
+    //     gpio_set_pin_pull_mode(tx->number, GPIO_PULL_OFF);
+    //     gpio_set_pin_function(tx->number, tx_pinmux);
+    //     self->tx_pin  = tx->number;
+    //     claim_pin(tx);
+    // } else {
+    //     self->tx_pin = NO_PIN;
+    // }
+
+    // if (have_rx) {
+    //     gpio_set_pin_direction(rx->number, GPIO_DIRECTION_IN);
+    //     gpio_set_pin_pull_mode(rx->number, GPIO_PULL_OFF);
+    //     gpio_set_pin_function(rx->number, rx_pinmux);
+    //     self->rx_pin  = rx->number;
+    //     claim_pin(rx);
+    // } else {
+    //     self->rx_pin = NO_PIN;
+    // }
+
+    // usart_async_enable(usart_desc_p);
+}
+
+bool common_hal_busio_uart_deinited(busio_uart_obj_t *self) {
+    return 0;//self->rx_pin == NO_PIN && self->tx_pin == NO_PIN;
+}
+
+void common_hal_busio_uart_deinit(busio_uart_obj_t *self) {
+    // if (common_hal_busio_uart_deinited(self)) {
+    //     return;
+    // }
+    // // This assignment is only here because the usart_async routines take a *const argument.
+    // struct usart_async_descriptor * const usart_desc_p = (struct usart_async_descriptor * const) &self->usart_desc;
+    // usart_async_disable(usart_desc_p);
+    // usart_async_deinit(usart_desc_p);
+    // reset_pin_number(self->rx_pin);
+    // reset_pin_number(self->tx_pin);
+    // self->rx_pin = NO_PIN;
+    // self->tx_pin = NO_PIN;
+}
+
+// Read characters.
+size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t len, int *errcode) {
+//     if (self->rx_pin == NO_PIN) {
+//         mp_raise_ValueError(translate("No RX pin"));
+//     }
+
+//     // This assignment is only here because the usart_async routines take a *const argument.
+//     struct usart_async_descriptor * const usart_desc_p = (struct usart_async_descriptor * const) &self->usart_desc;
+
+//     if (len == 0) {
+//         // Nothing to read.
+//         return 0;
+//     }
+
+//     struct io_descriptor *io;
+//     usart_async_get_io_descriptor(usart_desc_p, &io);
+
+//     size_t total_read = 0;
+//     uint64_t start_ticks = ticks_ms;
+
+//     // Busy-wait until timeout or until we've read enough chars.
+//     while (ticks_ms - start_ticks <= self->timeout_ms) {
+//         // Read as many chars as we can right now, up to len.
+//         size_t num_read = io_read(io, data, len);
+
+//         // Advance pointer in data buffer, and decrease how many chars left to read.
+//         data += num_read;
+//         len -= num_read;
+//         total_read += num_read;
+//         if (len == 0) {
+//             // Don't need to read any more: data buf is full.
+//             break;
+//         }
+//         if (num_read > 0) {
+//             // Reset the timeout on every character read.
+//             start_ticks = ticks_ms;
+//         }
+// #ifdef MICROPY_VM_HOOK_LOOP
+//         MICROPY_VM_HOOK_LOOP ;
+//         // Allow user to break out of a timeout with a KeyboardInterrupt.
+//         if (mp_hal_is_interrupted()) {
+//             break;
+//         }
+// #endif
+//         // If we are zero timeout, make sure we don't loop again (in the event
+//         // we read in under 1ms)
+//         if (self->timeout_ms == 0) {
+//             break;
+//         }
+//     }
+
+//     if (total_read == 0) {
+//         *errcode = EAGAIN;
+//         return MP_STREAM_ERROR;
+//     }
+
+    return 0;//total_read;
+}
+
+// Write characters.
+size_t common_hal_busio_uart_write(busio_uart_obj_t *self, const uint8_t *data, size_t len, int *errcode) {
+    // if (self->tx_pin == NO_PIN) {
+    //     mp_raise_ValueError(translate("No TX pin"));
+    // }
+
+    // // This assignment is only here because the usart_async routines take a *const argument.
+    // struct usart_async_descriptor * const usart_desc_p = (struct usart_async_descriptor * const) &self->usart_desc;
+
+    // struct io_descriptor *io;
+    // usart_async_get_io_descriptor(usart_desc_p, &io);
+
+    // if (io_write(io, data, len) < 0) {
+    //     *errcode = MP_EAGAIN;
+    //     return MP_STREAM_ERROR;
+    // }
+
+    // // Wait until write is complete or timeout.
+    // bool done = false;
+    // uint64_t start_ticks = ticks_ms;
+    // // Busy-wait for timeout.
+    // while (ticks_ms - start_ticks < self->timeout_ms) {
+    //     if (usart_async_is_tx_empty(usart_desc_p)) {
+    //         done = true;
+    //         break;
+    //     }
+    //     #ifdef MICROPY_VM_HOOK_LOOP
+    //         MICROPY_VM_HOOK_LOOP
+    //     #endif
+    // }
+
+    // if (!done) {
+    //     *errcode = MP_EAGAIN;
+    //     return MP_STREAM_ERROR;
+    // }
+
+    // // All the characters got written.
+    return 0;//len;
+}
+
+uint32_t common_hal_busio_uart_get_baudrate(busio_uart_obj_t *self) {
+    return 0;//self->baudrate;
+}
+
+void common_hal_busio_uart_set_baudrate(busio_uart_obj_t *self, uint32_t baudrate) {
+    // This assignment is only here because the usart_async routines take a *const argument.
+    // struct usart_async_descriptor * const usart_desc_p = (struct usart_async_descriptor * const) &self->usart_desc;
+    // usart_async_set_baud_rate(usart_desc_p,
+    //                           // Samples and ARITHMETIC vs FRACTIONAL must correspond to USART_SAMPR in
+    //                           // hpl_sercom_config.h.
+    //                           _usart_async_calculate_baud_rate(baudrate,  // e.g. 9600 baud
+    //                                                            PROTOTYPE_SERCOM_USART_ASYNC_CLOCK_FREQUENCY,
+    //                                                            16,   // samples
+    //                                                            USART_BAUDRATE_ASYNCH_ARITHMETIC,
+    //                                                            0  // fraction - not used for ARITHMETIC
+    //                                                            ));
+    // self->baudrate = baudrate;
+}
+
+uint32_t common_hal_busio_uart_rx_characters_available(busio_uart_obj_t *self) {
+    // // This assignment is only here because the usart_async routines take a *const argument.
+    // struct usart_async_descriptor * const usart_desc_p = (struct usart_async_descriptor * const) &self->usart_desc;
+    // struct usart_async_status async_status;
+    // usart_async_get_status(usart_desc_p, &async_status);
+    return 0;//async_status.rxcnt;
+}
+
+void common_hal_busio_uart_clear_rx_buffer(busio_uart_obj_t *self) {
+    // This assignment is only here because the usart_async routines take a *const argument.
+    // struct usart_async_descriptor * const usart_desc_p = (struct usart_async_descriptor * const) &self->usart_desc;
+    // usart_async_flush_rx_buffer(usart_desc_p);
+
+}
+
+bool common_hal_busio_uart_ready_to_tx(busio_uart_obj_t *self) {
+    // if (self->tx_pin == NO_PIN) {
+    //     return false;
+    // }
+    // // This assignment is only here because the usart_async routines take a *const argument.
+    // const struct _usart_async_device * const usart_device_p =
+    //     (struct _usart_async_device * const) &self->usart_desc.device;
+    return 0;//_usart_async_is_byte_sent(usart_device_p);
+}
diff --git a/ports/stm32f4/common-hal/busio/UART.h b/ports/stm32f4/common-hal/busio/UART.h
new file mode 100644
index 000000000..699233934
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/UART.h
@@ -0,0 +1,46 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 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.
+ */
+
+#ifndef MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_UART_H
+#define MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_UART_H
+
+#include "common-hal/microcontroller/Pin.h"
+
+#include "py/obj.h"
+
+typedef struct {
+    mp_obj_base_t base;
+    uint8_t rx_pin;
+    uint8_t tx_pin;
+    uint8_t character_bits;
+    bool rx_error;
+    uint32_t baudrate;
+    uint32_t timeout_ms;
+    uint32_t buffer_length;
+    uint8_t* buffer;
+} busio_uart_obj_t;
+
+#endif // MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_UART_H
diff --git a/ports/stm32f4/common-hal/busio/__init__.c b/ports/stm32f4/common-hal/busio/__init__.c
new file mode 100644
index 000000000..41761b674
--- /dev/null
+++ b/ports/stm32f4/common-hal/busio/__init__.c
@@ -0,0 +1 @@
+// No busio module functions.
diff --git a/ports/stm32f4/mpconfigport.mk b/ports/stm32f4/mpconfigport.mk
index 814bb2b20..88423c6d6 100644
--- a/ports/stm32f4/mpconfigport.mk
+++ b/ports/stm32f4/mpconfigport.mk
@@ -19,4 +19,5 @@ ifeq ($(MCU_SUB_VARIANT), stm32f412zx)
 	CIRCUITPY_BOARD = 1
 	CIRCUITPY_DIGITALIO = 1
 	CIRCUITPY_MICROCONTROLLER = 1
+	CIRCUITPY_BUSIO = 1
 endif