diff --git a/ports/stm32f4/boards/feather_stm32f405_express/stm32f4xx_hal_conf.h b/ports/stm32f4/boards/feather_stm32f405_express/stm32f4xx_hal_conf.h
index 7a1a9428f8..68a49b4ba8 100644
--- a/ports/stm32f4/boards/feather_stm32f405_express/stm32f4xx_hal_conf.h
+++ b/ports/stm32f4/boards/feather_stm32f405_express/stm32f4xx_hal_conf.h
@@ -63,7 +63,7 @@
 #define HAL_SPI_MODULE_ENABLED
 #define HAL_TIM_MODULE_ENABLED
 #define HAL_UART_MODULE_ENABLED   
-/* #define HAL_USART_MODULE_ENABLED   */
+#define HAL_USART_MODULE_ENABLED
 /* #define HAL_IRDA_MODULE_ENABLED   */
 /* #define HAL_SMARTCARD_MODULE_ENABLED   */
 /* #define HAL_WWDG_MODULE_ENABLED   */
diff --git a/ports/stm32f4/boards/stm32f412zg_discovery/mpconfigboard.mk b/ports/stm32f4/boards/stm32f412zg_discovery/mpconfigboard.mk
index 509a244106..d642f243ef 100644
--- a/ports/stm32f4/boards/stm32f412zg_discovery/mpconfigboard.mk
+++ b/ports/stm32f4/boards/stm32f412zg_discovery/mpconfigboard.mk
@@ -2,6 +2,7 @@ USB_VID = 0x239A
 USB_PID = 0x8056
 USB_PRODUCT = "STM32F412ZG Discovery Board - CPy"
 USB_MANUFACTURER = "STMicroelectronics"
+USB_DEVICES = "CDC,MSC,HID"
 
 INTERNAL_FLASH_FILESYSTEM = 1
 LONGINT_IMPL = NONE
diff --git a/ports/stm32f4/boards/stm32f412zg_discovery/pins.c b/ports/stm32f4/boards/stm32f412zg_discovery/pins.c
index b92f212700..ab90b04558 100644
--- a/ports/stm32f4/boards/stm32f412zg_discovery/pins.c
+++ b/ports/stm32f4/boards/stm32f412zg_discovery/pins.c
@@ -74,8 +74,8 @@ STATIC const mp_rom_map_elem_t board_module_globals_table[] = {
   { MP_ROM_QSTR(MP_QSTR_D4), MP_ROM_PTR(&pin_PG12) },
   { MP_ROM_QSTR(MP_QSTR_D3), MP_ROM_PTR(&pin_PF04) },
   { MP_ROM_QSTR(MP_QSTR_D2), MP_ROM_PTR(&pin_PG13) },
-  { MP_ROM_QSTR(MP_QSTR_D1), MP_ROM_PTR(&pin_PG14) },
-  { MP_ROM_QSTR(MP_QSTR_D0), MP_ROM_PTR(&pin_PG09) },
+  { MP_ROM_QSTR(MP_QSTR_D1), MP_ROM_PTR(&pin_PG14) }, //USART6 TX
+  { MP_ROM_QSTR(MP_QSTR_D0), MP_ROM_PTR(&pin_PG09) }, //USART6 RX
   { MP_ROM_QSTR(MP_QSTR_A0), MP_ROM_PTR(&pin_PA01) },
   { MP_ROM_QSTR(MP_QSTR_A1), MP_ROM_PTR(&pin_PC01) },
   { MP_ROM_QSTR(MP_QSTR_A2), MP_ROM_PTR(&pin_PC03) },
diff --git a/ports/stm32f4/common-hal/busio/UART.c b/ports/stm32f4/common-hal/busio/UART.c
index e1810b131e..c4ab237cd1 100644
--- a/ports/stm32f4/common-hal/busio/UART.c
+++ b/ports/stm32f4/common-hal/busio/UART.c
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2016 Damien P. George
+ * Copyright (c) 2019 Lucian Copeland for Adafruit Industries
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -36,45 +36,554 @@
 #include "supervisor/shared/translate.h"
 
 #include "tick.h"
+#include "stm32f4xx_hal.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,
+#define ALL_UARTS 0xFFFF
+
+STATIC bool reserved_uart[MAX_UART];
+int errflag; //Used to restart read halts
+
+STATIC void uart_clock_enable(uint16_t mask);
+STATIC void uart_clock_disable(uint16_t mask);
+STATIC void uart_assign_irq(busio_uart_obj_t* self, USART_TypeDef* USARTx);
+
+void uart_reset(void) {
+    for (uint8_t i = 0; i < MAX_UART; i++) {
+        reserved_uart[i] = false;
+        MP_STATE_PORT(cpy_uart_obj_all)[i] = NULL;
+    }
+    uart_clock_disable(ALL_UARTS);
+}
+
+STATIC USART_TypeDef * assign_uart_or_throw(busio_uart_obj_t* self, bool pin_eval, 
+                                            int uart_index, bool uart_taken) {
+    if (pin_eval) {
+        //assign a root pointer pointer for IRQ
+        MP_STATE_PORT(cpy_uart_obj_all)[uart_index] = self;
+        return mcu_uart_banks[uart_index];
+    } else {
+        if (uart_taken) {
+            mp_raise_ValueError(translate("Hardware in use, try alternative pins"));
+        } else {
+            mp_raise_ValueError(translate("Invalid UART pin selection"));
+        }
+    }
+}
+
+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,
         uint16_t receiver_buffer_size) {
-	mp_raise_NotImplementedError(translate("UART not yet supported"));
+
+    //match pins to UART objects
+    USART_TypeDef * USARTx;
+
+    uint8_t tx_len = sizeof(mcu_uart_tx_list)/sizeof(*mcu_uart_tx_list);
+    uint8_t rx_len = sizeof(mcu_uart_rx_list)/sizeof(*mcu_uart_rx_list);
+    bool uart_taken = false;
+    uint8_t uart_index = 0; //origin 0 corrected
+    
+    //Can have both pins, or either
+    if ((tx != mp_const_none) && (rx != mp_const_none)) {
+        //normal find loop if both pins exist
+        for (uint i = 0; i < tx_len; i++) {
+            if (mcu_uart_tx_list[i].pin == tx) {
+                //rx
+                for (uint j = 0; j < rx_len; j++) {
+                    if (mcu_uart_rx_list[j].pin == rx 
+                        && mcu_uart_rx_list[j].uart_index == mcu_uart_tx_list[i].uart_index) {
+                        //keep looking if the UART is taken, edge case
+                        if (reserved_uart[mcu_uart_tx_list[i].uart_index - 1]) {
+                            uart_taken = true;
+                            continue;
+                        }
+                        //store pins if not
+                        self->tx = &mcu_uart_tx_list[i];
+                        self->rx = &mcu_uart_rx_list[j];
+                        break;
+                    }
+                }
+            }
+        }
+        uart_index = self->tx->uart_index - 1;
+        USARTx = assign_uart_or_throw(self, (self->tx != NULL && self->rx != NULL), 
+            uart_index, uart_taken);
+    } else if (tx == mp_const_none) {
+        //If there is no tx, run only rx
+        for (uint i = 0; i < rx_len; i++) {
+            if (mcu_uart_rx_list[i].pin == rx) {
+                //keep looking if the UART is taken, edge case
+                if (reserved_uart[mcu_uart_rx_list[i].uart_index - 1]) {
+                    uart_taken = true;
+                    continue;
+                }
+                //store pins if not
+                self->rx = &mcu_uart_rx_list[i];
+                break;
+            }
+        }
+        uart_index = self->rx->uart_index - 1;
+        USARTx = assign_uart_or_throw(self, (self->rx != NULL), 
+            uart_index, uart_taken);
+    } else if (rx == mp_const_none) {
+        //If there is no rx, run only tx
+        for (uint i = 0; i < tx_len; i++) {
+            if (mcu_uart_tx_list[i].pin == tx) {
+                //keep looking if the UART is taken, edge case
+                if (reserved_uart[mcu_uart_tx_list[i].uart_index - 1]) {
+                    uart_taken = true;
+                    continue;
+                }
+                //store pins if not
+                self->tx = &mcu_uart_tx_list[i];
+                break;
+            }
+        }
+        uart_index = self->tx->uart_index - 1;
+        USARTx = assign_uart_or_throw(self, (self->tx != NULL), 
+            uart_index, uart_taken);
+    } else {
+        //both pins cannot be empty
+        mp_raise_ValueError(translate("Supply at least one UART pin"));
+    }
+
+    //Other errors
+    if ( receiver_buffer_size == 0 ) {
+        mp_raise_ValueError(translate("Invalid buffer size"));
+    }
+    if ( bits != 8 && bits != 9 ) {
+        mp_raise_ValueError(translate("Invalid word/bit length"));
+    }
+    if ( USARTx == NULL) { //this can only be hit if the periph file is wrong
+        mp_raise_ValueError(translate("Internal define error"));
+    }
+
+    //GPIO Init
+    GPIO_InitTypeDef GPIO_InitStruct = {0};
+    if (self->tx != NULL) {
+        GPIO_InitStruct.Pin = pin_mask(tx->number);
+        GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
+        GPIO_InitStruct.Pull = GPIO_PULLUP;
+        GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
+        GPIO_InitStruct.Alternate = self->tx->altfn_index;
+        HAL_GPIO_Init(pin_port(tx->port), &GPIO_InitStruct);
+    }
+    if (self->rx != NULL) {
+        GPIO_InitStruct.Pin = pin_mask(rx->number);
+        GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
+        GPIO_InitStruct.Pull = GPIO_PULLUP;
+        GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
+        GPIO_InitStruct.Alternate = self->rx->altfn_index; 
+        HAL_GPIO_Init(pin_port(rx->port), &GPIO_InitStruct);
+    }
+
+    //reserve uart and enable the peripheral
+    reserved_uart[uart_index] = true;
+    uart_clock_enable(1 << (uart_index));
+    uart_assign_irq(self, USARTx);
+
+    self->handle.Instance = USARTx;
+    self->handle.Init.BaudRate = baudrate;
+    self->handle.Init.WordLength = (bits == 9) ? UART_WORDLENGTH_9B : UART_WORDLENGTH_8B;
+    self->handle.Init.StopBits = (stop > 1) ? UART_STOPBITS_2 : UART_STOPBITS_1;
+    self->handle.Init.Parity = (parity == PARITY_ODD) ? UART_PARITY_ODD : 
+                               (parity == PARITY_EVEN) ? UART_PARITY_EVEN :
+                               UART_PARITY_NONE;
+    self->handle.Init.Mode = (self->tx != NULL && self->rx != NULL) ? UART_MODE_TX_RX :
+                             (self->tx != NULL) ? UART_MODE_TX :
+                             UART_MODE_RX;
+    self->handle.Init.HwFlowCtl = UART_HWCONTROL_NONE;
+    self->handle.Init.OverSampling = UART_OVERSAMPLING_16;
+    if (HAL_UART_Init(&self->handle) != HAL_OK)
+    {
+        mp_raise_ValueError(translate("UART Init Error"));
+
+    }
+
+    // Init buffer for rx and claim pins
+    if (self->rx != NULL) {
+        ringbuf_alloc(&self->rbuf, receiver_buffer_size, true);
+        if (!self->rbuf.buf) {
+            mp_raise_ValueError(translate("UART Buffer allocation error"));
+        }
+        claim_pin(rx);
+    }
+    if (self->tx != NULL) {
+        claim_pin(tx);
+    }
+    self->baudrate = baudrate;
+    self->timeout_ms = timeout * 1000;
+
+    //start the interrupt series
+    if ((HAL_UART_GetState(&self->handle) & HAL_UART_STATE_BUSY_RX) == HAL_UART_STATE_BUSY_RX) {
+        mp_raise_ValueError(translate("Could not start interrupt, RX busy"));
+    }
+
+    //start the receive interrupt chain
+    HAL_NVIC_DisableIRQ(self->irq); //prevent handle lock contention
+    HAL_UART_Receive_IT(&self->handle, &self->rx_char, 1);
+    HAL_NVIC_SetPriority(self->irq, UART_IRQPRI, UART_IRQSUB_PRI);
+    HAL_NVIC_EnableIRQ(self->irq);
+
+    errflag = HAL_OK;
 }
 
 bool common_hal_busio_uart_deinited(busio_uart_obj_t *self) {
-    return 0;
+    return self->tx->pin == mp_const_none;
 }
 
 void common_hal_busio_uart_deinit(busio_uart_obj_t *self) {
+    if (common_hal_busio_uart_deinited(self)) return;
+    
+    reset_pin_number(self->tx->pin->port,self->tx->pin->number);
+    reset_pin_number(self->rx->pin->port,self->rx->pin->number);
+    self->tx = mp_const_none;
+    self->rx = mp_const_none;
+    gc_free(self->rbuf.buf);
+    self->rbuf.size = 0;
+    self->rbuf.iput = self->rbuf.iget = 0;
 }
 
-// Read characters.
 size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t len, int *errcode) {
-    return 0;
+    if (self->rx == NULL) {
+        mp_raise_ValueError(translate("No RX pin"));
+    }
+
+    size_t rx_bytes = 0;
+    uint64_t start_ticks = ticks_ms;
+
+    // Wait for all bytes received or timeout, same as nrf
+    while ( (ringbuf_count(&self->rbuf) < len) && (ticks_ms - start_ticks < self->timeout_ms) ) {
+        RUN_BACKGROUND_TASKS;
+        //restart if it failed in the callback
+        if (errflag != HAL_OK) {
+            errflag = HAL_UART_Receive_IT(&self->handle, &self->rx_char, 1);
+        }
+        // Allow user to break out of a timeout with a KeyboardInterrupt.
+        if ( mp_hal_is_interrupted() ) {
+            return 0;
+        }
+    }
+
+    // Halt reception
+    HAL_NVIC_DisableIRQ(self->irq);
+    // copy received data
+    rx_bytes = ringbuf_count(&self->rbuf);
+    rx_bytes = MIN(rx_bytes, len);
+    for (uint16_t i = 0; i < rx_bytes; i++) {
+        data[i] = ringbuf_get(&self->rbuf);
+    }
+    HAL_NVIC_EnableIRQ(self->irq);
+
+    if (rx_bytes == 0) {
+        *errcode = EAGAIN;
+        return MP_STREAM_ERROR;
+    }
+    return rx_bytes; 
 }
 
 // Write characters.
 size_t common_hal_busio_uart_write(busio_uart_obj_t *self, const uint8_t *data, size_t len, int *errcode) {
-    return 0;
+    if (self->tx == NULL) {
+        mp_raise_ValueError(translate("No TX pin"));
+    }
+    bool write_err = false; //write error shouldn't disable interrupts
+
+    HAL_NVIC_DisableIRQ(self->irq);
+    if (HAL_UART_Transmit(&self->handle, (uint8_t*)data, len, self->timeout_ms) != HAL_OK) {
+        write_err = true;
+    }
+    HAL_UART_Receive_IT(&self->handle, &self->rx_char, 1);
+    HAL_NVIC_EnableIRQ(self->irq);
+
+    if (write_err) mp_raise_ValueError(translate("UART write error"));
+    return len;
+}
+
+void HAL_UART_RxCpltCallback(UART_HandleTypeDef *handle)
+{
+    for (int i = 0; i < 7; i++) {
+        //get context pointer and cast it as struct pointer
+        busio_uart_obj_t * context = (busio_uart_obj_t*)MP_STATE_PORT(cpy_uart_obj_all)[i];
+        if (handle == &context->handle) {
+            //check if transaction is ongoing
+            if ((HAL_UART_GetState(handle) & HAL_UART_STATE_BUSY_RX) == HAL_UART_STATE_BUSY_RX) {
+                return;
+            }
+            ringbuf_put_n(&context->rbuf, &context->rx_char, 1);
+            errflag = HAL_UART_Receive_IT(handle, &context->rx_char, 1);
+            
+            return;
+        }
+    }
+}
+
+void HAL_UART_ErrorCallback(UART_HandleTypeDef *UartHandle)
+{
+    if (__HAL_UART_GET_FLAG(UartHandle, UART_FLAG_PE) != RESET) {
+        __HAL_UART_CLEAR_PEFLAG(UartHandle);
+    } else if (__HAL_UART_GET_FLAG(UartHandle, UART_FLAG_FE) != RESET) {
+        __HAL_UART_CLEAR_FEFLAG(UartHandle);
+    } else if (__HAL_UART_GET_FLAG(UartHandle, UART_FLAG_NE) != RESET) {
+        __HAL_UART_CLEAR_NEFLAG(UartHandle);
+    } else if (__HAL_UART_GET_FLAG(UartHandle, UART_FLAG_ORE) != RESET) {
+        __HAL_UART_CLEAR_OREFLAG(UartHandle);
+    }
+    //restart serial read after an error
+    for (int i = 0; i < 7; i++) {
+        busio_uart_obj_t * context = (busio_uart_obj_t *)MP_STATE_PORT(cpy_uart_obj_all)[i];
+        if (UartHandle == &context->handle) {
+            HAL_UART_Receive_IT(UartHandle, &context->rx_char, 1);
+            return;
+        }
+    }
+
 }
 
 uint32_t common_hal_busio_uart_get_baudrate(busio_uart_obj_t *self) {
-    return 0;
+    return self->baudrate;
 }
 
 void common_hal_busio_uart_set_baudrate(busio_uart_obj_t *self, uint32_t baudrate) {
+    //Don't reset if it's the same value
+    if (baudrate == self->baudrate) return;
+
+    //Otherwise de-init and set new rate
+    if (HAL_UART_DeInit(&self->handle) != HAL_OK) {
+        mp_raise_ValueError(translate("UART De-init error"));
+    }
+    self->handle.Init.BaudRate = baudrate;
+    if (HAL_UART_Init(&self->handle) != HAL_OK) {
+        mp_raise_ValueError(translate("UART Re-init error"));
+    }
+
+    self->baudrate = baudrate;
 }
 
 uint32_t common_hal_busio_uart_rx_characters_available(busio_uart_obj_t *self) {
-    return 0;
+    return ringbuf_count(&self->rbuf);
 }
 
 void common_hal_busio_uart_clear_rx_buffer(busio_uart_obj_t *self) {
+    // Halt reception
+    HAL_NVIC_DisableIRQ(self->irq);
+    ringbuf_clear(&self->rbuf);
+    HAL_NVIC_EnableIRQ(self->irq);
 }
 
 bool common_hal_busio_uart_ready_to_tx(busio_uart_obj_t *self) {
-    return 0;
+    return __HAL_UART_GET_FLAG(&self->handle, UART_FLAG_TXE);
+}
+
+STATIC void call_hal_irq(int uart_num) {
+    //Create casted context pointer
+    busio_uart_obj_t * context = (busio_uart_obj_t*)MP_STATE_PORT(cpy_uart_obj_all)[uart_num - 1];
+    if (context != NULL) {
+        HAL_NVIC_ClearPendingIRQ(context->irq);
+        HAL_UART_IRQHandler(&context->handle);
+    }
+}
+
+// UART/USART IRQ handlers
+void USART1_IRQHandler(void) {
+    call_hal_irq(1);
+}
+
+void USART2_IRQHandler(void) {
+    call_hal_irq(2);
+}
+
+void USART3_IRQHandler(void) {
+    call_hal_irq(3);
+}
+
+void UART4_IRQHandler(void) {
+    call_hal_irq(4);
+}
+
+void UART5_IRQHandler(void) {
+    call_hal_irq(5);
+}
+
+void USART6_IRQHandler(void) {
+    call_hal_irq(6);
+}
+
+STATIC void uart_clock_enable(uint16_t mask) {
+    #ifdef USART1
+    if (mask & (1 << 0)) {
+        __HAL_RCC_USART1_FORCE_RESET();
+        __HAL_RCC_USART1_RELEASE_RESET();
+        __HAL_RCC_USART1_CLK_ENABLE(); 
+    }
+    #endif
+    #ifdef USART2
+    if (mask & (1 << 1)) {
+        __HAL_RCC_USART2_FORCE_RESET();
+        __HAL_RCC_USART2_RELEASE_RESET();
+        __HAL_RCC_USART2_CLK_ENABLE(); 
+    }
+    #endif
+    #ifdef USART3
+    if (mask & (1 << 2)) {
+        __HAL_RCC_USART3_FORCE_RESET();
+        __HAL_RCC_USART3_RELEASE_RESET();
+        __HAL_RCC_USART3_CLK_ENABLE(); 
+    }
+    #endif
+    #ifdef UART4
+    if (mask & (1 << 3)) {
+        __HAL_RCC_UART4_FORCE_RESET();
+        __HAL_RCC_UART4_RELEASE_RESET();
+        __HAL_RCC_UART4_CLK_ENABLE(); 
+    }
+    #endif
+    #ifdef UART5
+    if (mask & (1 << 4)) {
+        __HAL_RCC_UART5_FORCE_RESET();
+        __HAL_RCC_UART5_RELEASE_RESET();
+        __HAL_RCC_UART5_CLK_ENABLE(); 
+    }
+    #endif
+    #ifdef USART6
+    if (mask & (1 << 5)) {
+        __HAL_RCC_USART6_FORCE_RESET();
+        __HAL_RCC_USART6_RELEASE_RESET();
+        __HAL_RCC_USART6_CLK_ENABLE(); 
+    } 
+    #endif
+    #ifdef UART7
+    if (mask & (1 << 6)) {
+        __HAL_RCC_UART7_FORCE_RESET();
+        __HAL_RCC_UART7_RELEASE_RESET();
+        __HAL_RCC_UART7_CLK_ENABLE(); 
+    } 
+    #endif
+    #ifdef UART8
+    if (mask & (1 << 7)) {
+        __HAL_RCC_UART8_FORCE_RESET();
+        __HAL_RCC_UART8_RELEASE_RESET();
+        __HAL_RCC_UART8_CLK_ENABLE(); 
+    } 
+    #endif
+    #ifdef UART9
+    if (mask & (1 << 8)) {
+        __HAL_RCC_UART9_FORCE_RESET();
+        __HAL_RCC_UART9_RELEASE_RESET();
+        __HAL_RCC_UART9_CLK_ENABLE(); 
+    } 
+    #endif
+    #ifdef UART10
+    if (mask & (1 << 9)) {
+        __HAL_RCC_UART10_FORCE_RESET();
+        __HAL_RCC_UART10_RELEASE_RESET();
+        __HAL_RCC_UART10_CLK_ENABLE(); 
+    } 
+    #endif
+}
+
+STATIC void uart_clock_disable(uint16_t mask) {
+    #ifdef USART1
+    if (mask & (1 << 0)) {
+        __HAL_RCC_USART1_FORCE_RESET();
+        __HAL_RCC_USART1_RELEASE_RESET();
+        __HAL_RCC_USART1_CLK_DISABLE(); 
+    }
+    #endif
+    #ifdef USART2
+    if (mask & (1 << 1)) {
+        __HAL_RCC_USART2_FORCE_RESET();
+        __HAL_RCC_USART2_RELEASE_RESET();
+        __HAL_RCC_USART2_CLK_DISABLE(); 
+    }
+    #endif
+    #ifdef USART3
+    if (mask & (1 << 2)) {
+        __HAL_RCC_USART3_FORCE_RESET();
+        __HAL_RCC_USART3_RELEASE_RESET();
+        __HAL_RCC_USART3_CLK_DISABLE(); 
+    }
+    #endif
+    #ifdef UART4
+    if (mask & (1 << 3)) {
+        __HAL_RCC_UART4_FORCE_RESET();
+        __HAL_RCC_UART4_RELEASE_RESET();
+        __HAL_RCC_UART4_CLK_DISABLE(); 
+    }
+    #endif
+    #ifdef UART5
+    if (mask & (1 << 4)) {
+        __HAL_RCC_UART5_FORCE_RESET();
+        __HAL_RCC_UART5_RELEASE_RESET();
+        __HAL_RCC_UART5_CLK_DISABLE(); 
+    }
+    #endif
+    #ifdef USART6
+    if (mask & (1 << 5)) {
+        __HAL_RCC_USART6_FORCE_RESET();
+        __HAL_RCC_USART6_RELEASE_RESET();
+        __HAL_RCC_USART6_CLK_DISABLE(); 
+    } 
+    #endif
+    #ifdef UART7
+    if (mask & (1 << 6)) {
+        __HAL_RCC_UART7_FORCE_RESET();
+        __HAL_RCC_UART7_RELEASE_RESET();
+        __HAL_RCC_UART7_CLK_DISABLE(); 
+    } 
+    #endif
+    #ifdef UART8
+    if (mask & (1 << 7)) {
+        __HAL_RCC_UART8_FORCE_RESET();
+        __HAL_RCC_UART8_RELEASE_RESET();
+        __HAL_RCC_UART8_CLK_DISABLE(); 
+    } 
+    #endif
+    #ifdef UART9
+    if (mask & (1 << 8)) {
+        __HAL_RCC_UART9_FORCE_RESET();
+        __HAL_RCC_UART9_RELEASE_RESET();
+        __HAL_RCC_UART9_CLK_DISABLE(); 
+    } 
+    #endif
+    #ifdef UART10
+    if (mask & (1 << 9)) {
+        __HAL_RCC_UART10_FORCE_RESET();
+        __HAL_RCC_UART10_RELEASE_RESET();
+        __HAL_RCC_UART10_CLK_DISABLE(); 
+    } 
+    #endif
+}
+
+STATIC void uart_assign_irq(busio_uart_obj_t *self, USART_TypeDef * USARTx) {
+    #ifdef USART1
+    if (USARTx == USART1) self->irq = USART1_IRQn;
+    #endif
+    #ifdef USART2
+    if (USARTx == USART2) self->irq = USART2_IRQn;
+    #endif
+    #ifdef USART3
+    if (USARTx == USART3) self->irq = USART3_IRQn;
+    #endif
+    #ifdef UART4
+    if (USARTx == UART4) self->irq = UART4_IRQn;
+    #endif
+    #ifdef UART5
+    if (USARTx == UART5) self->irq = UART5_IRQn;
+    #endif
+    #ifdef USART6
+    if (USARTx == USART6) self->irq = USART6_IRQn;
+    #endif
+    #ifdef UART7
+    if (USARTx == UART7) self->irq = UART7_IRQn;
+    #endif
+    #ifdef UART8
+    if (USARTx == UART8) self->irq = UART8_IRQn;
+    #endif
+    #ifdef UART9
+    if (USARTx == UART9) self->irq = UART9_IRQn;
+    #endif
+    #ifdef UART10
+    if (USARTx == UART10) self->irq = UART10_IRQn;
+    #endif
 }
diff --git a/ports/stm32f4/common-hal/busio/UART.h b/ports/stm32f4/common-hal/busio/UART.h
index 6992339340..cde5fadd00 100644
--- a/ports/stm32f4/common-hal/busio/UART.h
+++ b/ports/stm32f4/common-hal/busio/UART.h
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2016 Scott Shawcroft
+ * Copyright (c) 2019 Lucian Copeland for Adafruit Industries
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,19 +28,33 @@
 #define MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_UART_H
 
 #include "common-hal/microcontroller/Pin.h"
+#include "stm32f4/periph.h"
+#include "stm32f4xx_hal.h" 
 
 #include "py/obj.h"
+#include "py/ringbuf.h"
+
+#ifndef UART_IRQPRI
+#define UART_IRQPRI       1
+#endif
+#ifndef UART_IRQSUB_PRI
+#define UART_IRQSUB_PRI    0
+#endif
 
 typedef struct {
     mp_obj_base_t base;
-    uint8_t rx_pin;
-    uint8_t tx_pin;
-    uint8_t character_bits;
-    bool rx_error;
+    UART_HandleTypeDef handle;
+    IRQn_Type irq;
+    const mcu_uart_tx_obj_t *tx;
+    const mcu_uart_rx_obj_t *rx;
+
+    ringbuf_t rbuf;
+    uint8_t rx_char;
+
     uint32_t baudrate;
     uint32_t timeout_ms;
-    uint32_t buffer_length;
-    uint8_t* buffer;
 } busio_uart_obj_t;
 
+void uart_reset(void);
+
 #endif // MICROPY_INCLUDED_STM32F4_COMMON_HAL_BUSIO_UART_H
diff --git a/ports/stm32f4/mpconfigport.h b/ports/stm32f4/mpconfigport.h
index 543a55942e..7737bda8d4 100644
--- a/ports/stm32f4/mpconfigport.h
+++ b/ports/stm32f4/mpconfigport.h
@@ -39,7 +39,10 @@
 
 #include "py/circuitpy_mpconfig.h"
 
+#define MAX_UART 10 //how many UART are implemented
+
 #define MICROPY_PORT_ROOT_POINTERS \
+    void *cpy_uart_obj_all[MAX_UART]; \
 	CIRCUITPY_COMMON_ROOT_POINTERS
 
 #endif  // __INCLUDED_MPCONFIGPORT_H
diff --git a/ports/stm32f4/peripherals/stm32f4/periph.h b/ports/stm32f4/peripherals/stm32f4/periph.h
index d066b2be77..4b00ce1d92 100644
--- a/ports/stm32f4/peripherals/stm32f4/periph.h
+++ b/ports/stm32f4/peripherals/stm32f4/periph.h
@@ -34,8 +34,8 @@
 #include "stm32f4/pins.h"
 
 // I2C 
-//TODO: these objects should be condensed into a single 'periph_pin' unless we
-//find a compelling reason to store more unique data in them. 
+// TODO: these objects should be condensed into a single 'periph_pin' unless we
+// find a compelling reason to store more unique data in them. 
 
 typedef struct {
     uint8_t i2c_index:4; // Index of the I2C unit (1 to 3)
@@ -65,8 +65,8 @@ typedef struct {
 }
 
 // SPI 
-//TODO: these objects should be condensed into a single 'periph_pin' unless we
-//find a compelling reason to store more unique data in them. 
+// TODO: these objects should be condensed into a single 'periph_pin' unless we
+// find a compelling reason to store more unique data in them. 
 
 typedef struct {
     uint8_t spi_index:4; //Up to 6 SPI units
@@ -99,6 +99,29 @@ typedef struct {
     .pin = spi_pin, \
 }
 
+// UART
+// TODO: these objects should be condensed into a single 'periph_pin' unless we
+// find a compelling reason to store more unique data in them. 
+
+typedef struct {
+    uint8_t uart_index:4; 
+    uint8_t altfn_index:4; 
+    const mcu_pin_obj_t * pin;
+} mcu_uart_tx_obj_t;
+
+typedef struct {
+    uint8_t uart_index:4; 
+    uint8_t altfn_index:4; 
+    const mcu_pin_obj_t * pin;
+} mcu_uart_rx_obj_t;
+
+#define UART(index, alt, uart_pin)       \
+{ \
+    .uart_index = index, \
+    .altfn_index = alt, \
+    .pin = uart_pin, \
+}
+
 //Timers
 typedef struct {
     uint8_t tim_index:4; 
diff --git a/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.c b/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.c
index 67faacdf6b..bc03f7c7be 100644
--- a/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.c
+++ b/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.c
@@ -86,6 +86,39 @@ const mcu_spi_nss_obj_t mcu_spi_nss_list[6] = {
     SPI(3, 6, &pin_PA15),
 };
 
+USART_TypeDef * mcu_uart_banks[MAX_UART] = {USART1, USART2, USART3, UART4, UART5, USART6};
+bool mcu_uart_has_usart[MAX_UART] = {true, true, true, false, false, true};
+
+const mcu_uart_tx_obj_t mcu_uart_tx_list[12] = {
+    UART(4, 8, &pin_PA00),
+    UART(2, 7, &pin_PA02),
+    UART(1, 7, &pin_PA09),
+    UART(1, 7, &pin_PB06),
+    UART(3, 7, &pin_PB10),
+    UART(6, 8, &pin_PC06),
+    UART(3, 7, &pin_PC10),
+    UART(4, 8, &pin_PC10),
+    UART(5, 8, &pin_PC12),
+    UART(2, 7, &pin_PD05),
+    UART(3, 7, &pin_PD08),
+    UART(6, 8, &pin_PG14),
+};
+
+const mcu_uart_rx_obj_t mcu_uart_rx_list[12] = {
+    UART(4, 8, &pin_PA01),
+    UART(2, 7, &pin_PA03),
+    UART(1, 7, &pin_PA10),
+    UART(1, 7, &pin_PB07),
+    UART(3, 7, &pin_PB11),
+    UART(6, 8, &pin_PC07),
+    UART(3, 7, &pin_PC11),
+    UART(4, 8, &pin_PC11),
+    UART(5, 8, &pin_PD02),
+    UART(2, 7, &pin_PD06),
+    UART(3, 7, &pin_PD09),
+    UART(6, 8, &pin_PG09),
+};
+
 //Timers
 //TIM6 and TIM7 are basic timers that are only used by DAC, and don't have pins
 TIM_TypeDef * mcu_tim_banks[14] = {TIM1, TIM2, TIM3, TIM4, TIM5, NULL, NULL, TIM8, TIM9, TIM10,
@@ -159,4 +192,3 @@ const mcu_tim_pin_obj_t mcu_tim_pin_list[56] = {
     // TIM(8,3,2,&pin_PI06),
     // TIM(8,3,3,&pin_PI07),
 };
-
diff --git a/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.h b/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.h
index 89298cdab4..e87e798574 100644
--- a/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.h
+++ b/ports/stm32f4/peripherals/stm32f4/stm32f405xx/periph.h
@@ -41,10 +41,17 @@ extern const mcu_spi_mosi_obj_t mcu_spi_mosi_list[6];
 extern const mcu_spi_miso_obj_t mcu_spi_miso_list[6];
 extern const mcu_spi_nss_obj_t mcu_spi_nss_list[6];
 
+//UART
+extern USART_TypeDef * mcu_uart_banks[MAX_UART];
+extern bool mcu_uart_has_usart[MAX_UART];
+
+extern const mcu_uart_tx_obj_t mcu_uart_tx_list[12];
+extern const mcu_uart_rx_obj_t mcu_uart_rx_list[12];
+
+//Timers
 #define TIM_BANK_ARRAY_LEN 14
 #define TIM_PIN_ARRAY_LEN 56
 TIM_TypeDef * mcu_tim_banks[TIM_BANK_ARRAY_LEN];
 const mcu_tim_pin_obj_t mcu_tim_pin_list[TIM_PIN_ARRAY_LEN];
 
-
 #endif // MICROPY_INCLUDED_STM32F4_PERIPHERALS_STM32F405XX_PERIPH_H
\ No newline at end of file
diff --git a/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.c b/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.c
index 1d4034bbf1..b7d9edf4f7 100644
--- a/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.c
+++ b/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.c
@@ -119,7 +119,28 @@ const mcu_spi_nss_obj_t mcu_spi_nss_list[12] = {
     SPI(5, 6, &pin_PE11)
 };
 
-//UART, Etc
+USART_TypeDef * mcu_uart_banks[MAX_UART] = {USART1, USART2, NULL, NULL, NULL, USART6};
+bool mcu_uart_has_usart[MAX_UART] = {true, true, false, false, false, true};
+
+const mcu_uart_tx_obj_t mcu_uart_tx_list[7] = {
+    UART(2, 7, &pin_PA02),
+    UART(1, 7, &pin_PA09),
+    UART(1, 7, &pin_PA15),
+    UART(6, 8, &pin_PA11),
+    UART(1, 7, &pin_PB06),
+    UART(6, 8, &pin_PC06),
+    UART(2, 7, &pin_PD05),
+};
+
+const mcu_uart_rx_obj_t mcu_uart_rx_list[7] = {
+    UART(2, 7, &pin_PA03),
+    UART(1, 7, &pin_PA10),
+    UART(6, 8, &pin_PA12),
+    UART(1, 7, &pin_PB03),
+    UART(1, 7, &pin_PB07),
+    UART(6, 8, &pin_PC07),
+    UART(2, 7, &pin_PD06),
+};
 
 //Timers
 //TIM6 and TIM7 are basic timers that are only used by DAC, and don't have pins
@@ -171,4 +192,3 @@ const mcu_tim_pin_obj_t mcu_tim_pin_list[44] = {
     TIM(1,1,3,&pin_PE13),
     TIM(1,1,4,&pin_PE14),
 };
-
diff --git a/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.h b/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.h
index 3045397a35..d657d73b68 100644
--- a/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.h
+++ b/ports/stm32f4/peripherals/stm32f4/stm32f411xe/periph.h
@@ -41,9 +41,17 @@ extern const mcu_spi_mosi_obj_t mcu_spi_mosi_list[14];
 extern const mcu_spi_miso_obj_t mcu_spi_miso_list[12];
 extern const mcu_spi_nss_obj_t mcu_spi_nss_list[12];
 
+//UART
+extern USART_TypeDef * mcu_uart_banks[MAX_UART];
+extern bool mcu_uart_has_usart[MAX_UART];
+
+extern const mcu_uart_tx_obj_t mcu_uart_tx_list[7];
+extern const mcu_uart_rx_obj_t mcu_uart_rx_list[7];
+
+//Timers
 #define TIM_BANK_ARRAY_LEN 14
-TIM_TypeDef * mcu_tim_banks[14];
 #define TIM_PIN_ARRAY_LEN 44
-const mcu_tim_pin_obj_t mcu_tim_pin_list[44];
+TIM_TypeDef * mcu_tim_banks[TIM_BANK_ARRAY_LEN];
+const mcu_tim_pin_obj_t mcu_tim_pin_list[TIM_PIN_ARRAY_LEN];
 
 #endif // MICROPY_INCLUDED_STM32F4_PERIPHERALS_STM32F411VE_PERIPH_H
\ No newline at end of file
diff --git a/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.c b/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.c
index edce2845b8..f5effa80ed 100644
--- a/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.c
+++ b/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.c
@@ -120,7 +120,39 @@ const mcu_spi_nss_obj_t mcu_spi_nss_list[12] = {
     SPI(5, 6, &pin_PE11)
 };
 
-//UART, Etc
+//UART
+
+USART_TypeDef * mcu_uart_banks[MAX_UART] = {USART1, USART2, USART3, NULL, NULL, USART6};
+bool mcu_uart_has_usart[MAX_UART] = {true, true, true, false, false, true};
+
+const mcu_uart_tx_obj_t mcu_uart_tx_list[11] = {
+    UART(2, 7, &pin_PA02),
+    UART(1, 7, &pin_PA09),
+    UART(1, 7, &pin_PA15),
+    UART(6, 8, &pin_PA11),
+    UART(1, 7, &pin_PB06),
+    UART(3, 7, &pin_PB10),
+    UART(6, 8, &pin_PC06),
+    UART(3, 7, &pin_PC10),
+    UART(2, 7, &pin_PD05),
+    UART(3, 7, &pin_PD08),
+    UART(6, 8, &pin_PG14),
+};
+
+const mcu_uart_rx_obj_t mcu_uart_rx_list[12] = {
+    UART(2, 7, &pin_PA03),
+    UART(1, 7, &pin_PA10),
+    UART(6, 8, &pin_PA12),
+    UART(1, 7, &pin_PB03),
+    UART(1, 7, &pin_PB07),
+    UART(3, 7, &pin_PB11),
+    UART(3, 7, &pin_PC05),
+    UART(6, 8, &pin_PC07),
+    UART(3, 7, &pin_PC11),
+    UART(2, 7, &pin_PD06),
+    UART(3, 7, &pin_PD09),
+    UART(6, 8, &pin_PG09),
+};
 
 //Timers
 //TIM6 and TIM7 are basic timers that are only used by DAC, and don't have pins
diff --git a/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.h b/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.h
index 49ba108273..e0141e6dab 100644
--- a/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.h
+++ b/ports/stm32f4/peripherals/stm32f4/stm32f412zx/periph.h
@@ -42,9 +42,17 @@ extern const mcu_spi_mosi_obj_t mcu_spi_mosi_list[14];
 extern const mcu_spi_miso_obj_t mcu_spi_miso_list[12];
 extern const mcu_spi_nss_obj_t mcu_spi_nss_list[12];
 
+//UART
+extern USART_TypeDef * mcu_uart_banks[MAX_UART];
+extern bool mcu_uart_has_usart[MAX_UART];
+
+extern const mcu_uart_tx_obj_t mcu_uart_tx_list[11];
+extern const mcu_uart_rx_obj_t mcu_uart_rx_list[12];
+
+//Timers
 #define TIM_BANK_ARRAY_LEN 14
-TIM_TypeDef * mcu_tim_banks[14];
 #define TIM_PIN_ARRAY_LEN 60
-const mcu_tim_pin_obj_t mcu_tim_pin_list[60];
+TIM_TypeDef * mcu_tim_banks[TIM_BANK_ARRAY_LEN];
+const mcu_tim_pin_obj_t mcu_tim_pin_list[TIM_PIN_ARRAY_LEN];
 
 #endif // MICROPY_INCLUDED_STM32F4_PERIPHERALS_STM32F411VE_PERIPH_H
\ No newline at end of file
diff --git a/ports/stm32f4/supervisor/port.c b/ports/stm32f4/supervisor/port.c
index 602bec4be8..df5a70cd12 100644
--- a/ports/stm32f4/supervisor/port.c
+++ b/ports/stm32f4/supervisor/port.c
@@ -33,6 +33,7 @@
 #include "common-hal/microcontroller/Pin.h"
 #include "common-hal/busio/I2C.h"
 #include "common-hal/busio/SPI.h"
+#include "common-hal/busio/UART.h"
 #include "common-hal/pulseio/PWMOut.h"
 
 #include "stm32f4/clocks.h"
@@ -41,12 +42,12 @@
 #include "stm32f4xx_hal.h"
 
 safe_mode_t port_init(void) {
-	HAL_Init();
+    HAL_Init();
     __HAL_RCC_SYSCFG_CLK_ENABLE();
     __HAL_RCC_PWR_CLK_ENABLE();
 
-	stm32f4_peripherals_clocks_init();
-	stm32f4_peripherals_gpio_init();
+    stm32f4_peripherals_clocks_init();
+    stm32f4_peripherals_gpio_init();
 
     tick_init();
     board_init(); 
@@ -55,9 +56,10 @@ safe_mode_t port_init(void) {
 }
 
 void reset_port(void) {
-	reset_all_pins();
+    reset_all_pins();
     i2c_reset();
     spi_reset();
+    uart_reset();
     pwmout_reset();
 }
 
@@ -66,7 +68,7 @@ void reset_to_bootloader(void) {
 }
 
 void reset_cpu(void) {
-	NVIC_SystemReset();
+    NVIC_SystemReset();
 }
 
 uint32_t *port_stack_get_limit(void) {
@@ -88,7 +90,7 @@ uint32_t port_get_saved_word(void) {
 }
 
 void HardFault_Handler(void) {
-	reset_into_safe_mode(HARD_CRASH);
+    reset_into_safe_mode(HARD_CRASH);
     while (true) {
         asm("nop;");
     }
diff --git a/ports/stm32f4/tick.c b/ports/stm32f4/tick.c
index 43521fb516..688f71dbd4 100644
--- a/ports/stm32f4/tick.c
+++ b/ports/stm32f4/tick.c
@@ -62,6 +62,11 @@ uint32_t HAL_GetTick(void) //override ST HAL
 void tick_init() {
     uint32_t ticks_per_ms = SystemCoreClock/ 1000;
     SysTick_Config(ticks_per_ms); // interrupt is enabled
+
+    NVIC_EnableIRQ(SysTick_IRQn);
+    // Bump up the systick interrupt so nothing else interferes with timekeeping.
+    NVIC_SetPriority(SysTick_IRQn, 0);
+    NVIC_SetPriority(OTG_FS_IRQn, 1);
 }
 
 void tick_delay(uint32_t us) {