mimxrt/machine_uart: Add the UART class to the machine module.

The implementation uses the LPUARTx devices.  Up to 8 UARTs can be used,
given that the pins are accessible.  E.g. 8 on Teensy 4.1, 5 on
MIMXRT1020_EVK.

For Tennsy 4.0 and 4.1 the UART numbers are as printed on the pinout 1..N.
The MIMXRT10xx-EVK boards have only one UART named, which gets the number
1.  All other UART are assigned to different Pins:

MIMXRT1010-EVK:
    D0/D1   UART 1
    D6/D7   UART 2
    A0/D4   UART 3

MIMXRT1020-EVK:
    D0/D1   UART 1
    D6/D9   UART 2
    D10/D12 UART 3
    D14/D15 UART 4
    A0/A1   UART 5

MIMXRT1050-EVK, MIMXRT1060-EVK, MIMXRT1064-EVK:
    D0/D1   UART 1
    D7/D6   UART 2
    D8/D9   UART 3
    A1/A0   UART 4

15 files changed, 589 insertions, 82 deletions

diff --git a/ports/mimxrt/Makefile b/ports/mimxrt/Makefile
index cacbcc1a3..3af2a5547 100644
--- a/ports/mimxrt/Makefile
+++ b/ports/mimxrt/Makefile
@@ -140,6 +140,7 @@ SRC_C = \
 	machine_pin.c \
 	machine_rtc.c \
 	machine_timer.c \
+	machine_uart.c \
 	mimxrt_flash.c \
 	modutime.c \
 	modmachine.c \
@@ -263,6 +264,7 @@ SRC_QSTR += \
 	machine_pin.c \
 	machine_rtc.c \
 	machine_timer.c \
+	machine_uart.c \
 	mimxrt_flash.c \
 	modutime.c \
 	modmachine.c \
diff --git a/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.h b/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.h
index 3eb326812..5a373a3ca 100644
--- a/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.h
+++ b/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.h
@@ -8,3 +8,17 @@
 #define MICROPY_HW_LED_ON(pin) (mp_hal_pin_high(pin))
 #define MICROPY_HW_LED_OFF(pin) (mp_hal_pin_low(pin))
 #define BOARD_FLASH_CONFIG_HEADER_H "evkmimxrt1010_flexspi_nor_config.h"
+
+// Define mapping logical UART # to hardware UART #
+// LPUART1 on D0/D1 -> 1
+// LPUART3 on A0/D4 -> 3
+// LPUART4 on D6/D7 -> 2
+
+#define MICROPY_HW_UART_NUM     (sizeof(uart_index_table) / sizeof(uart_index_table)[0])
+#define MICROPY_HW_UART_INDEX   { 0, 1, 4, 3 }
+
+#define IOMUX_TABLE_UART \
+    { IOMUXC_GPIO_10_LPUART1_TXD }, { IOMUXC_GPIO_09_LPUART1_RXD }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_08_LPUART3_TXD }, { IOMUXC_GPIO_AD_07_LPUART3_RXD }, \
+    { IOMUXC_GPIO_AD_02_LPUART4_TXD }, { IOMUXC_GPIO_AD_01_LPUART4_RXD },
diff --git a/ports/mimxrt/boards/MIMXRT1010_EVK/pins.csv b/ports/mimxrt/boards/MIMXRT1010_EVK/pins.csv
index f7fdf3964..1f01215dd 100644
--- a/ports/mimxrt/boards/MIMXRT1010_EVK/pins.csv
+++ b/ports/mimxrt/boards/MIMXRT1010_EVK/pins.csv
@@ -34,24 +34,3 @@ PWM_CB,GPIO_05
 ENC_A,GPIO_AD_05
 ENC_B,GPIO_AD_06
 LED_GREEN,GPIO_11
-GPIO_01,GPIO_01
-GPIO_02,GPIO_02
-GPIO_03,GPIO_03
-GPIO_04,GPIO_04
-GPIO_05,GPIO_05
-GPIO_06,GPIO_06
-GPIO_08,GPIO_08
-GPIO_09,GPIO_09
-GPIO_10,GPIO_10
-GPIO_11,GPIO_11
-GPIO_AD_01,GPIO_AD_01
-GPIO_AD_02,GPIO_AD_02
-GPIO_AD_03,GPIO_AD_03
-GPIO_AD_04,GPIO_AD_04
-GPIO_AD_05,GPIO_AD_05
-GPIO_AD_06,GPIO_AD_06
-GPIO_AD_07,GPIO_AD_07
-GPIO_AD_09,GPIO_AD_09
-GPIO_AD_10,GPIO_AD_10
-GPIO_AD_14,GPIO_AD_14
-GPIO_SD_02,GPIO_SD_02
diff --git a/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.h b/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.h
index a025c85bf..5a595074a 100644
--- a/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.h
+++ b/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.h
@@ -9,3 +9,24 @@
 #define MICROPY_HW_LED_ON(pin) (mp_hal_pin_low(pin))
 #define MICROPY_HW_LED_OFF(pin) (mp_hal_pin_high(pin))
 #define BOARD_FLASH_CONFIG_HEADER_H "evkmimxrt1020_flexspi_nor_config.h"
+
+// Define mapping logical UART # to hardware UART #
+// D3/D5   LPUART1  Not usable, Since D3 is blocked.
+// D0/D1   LPUART2 -> 1
+// D6/D9   LPUART3 -> 2
+// D10/D12 LPUART5 -> 3
+// D14/D15 LPUART8 -> 4
+// A0/A1   LPUART4 -> 5
+
+#define MICROPY_HW_UART_NUM     (sizeof(uart_index_table) / sizeof(uart_index_table)[0])
+#define MICROPY_HW_UART_INDEX   { 0, 2, 3, 5, 8, 4 }
+
+#define IOMUX_TABLE_UART \
+    { IOMUXC_GPIO_AD_B0_06_LPUART1_TX }, { IOMUXC_GPIO_AD_B0_07_LPUART1_RX }, \
+    { IOMUXC_GPIO_AD_B1_08_LPUART2_TX }, { IOMUXC_GPIO_AD_B1_09_LPUART2_RX }, \
+    { IOMUXC_GPIO_AD_B0_14_LPUART3_TX }, { IOMUXC_GPIO_AD_B0_15_LPUART3_RX }, \
+    { IOMUXC_GPIO_AD_B1_10_LPUART4_TX }, { IOMUXC_GPIO_AD_B1_11_LPUART4_RX }, \
+    { IOMUXC_GPIO_AD_B0_10_LPUART5_TX }, { IOMUXC_GPIO_AD_B0_11_LPUART5_RX }, \
+    { 0 }, { 0 }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_SD_B1_02_LPUART8_TX }, { IOMUXC_GPIO_SD_B1_03_LPUART8_RX },
diff --git a/ports/mimxrt/boards/MIMXRT1050_EVK/mpconfigboard.h b/ports/mimxrt/boards/MIMXRT1050_EVK/mpconfigboard.h
index 9b7664841..51e0e2dc4 100644
--- a/ports/mimxrt/boards/MIMXRT1050_EVK/mpconfigboard.h
+++ b/ports/mimxrt/boards/MIMXRT1050_EVK/mpconfigboard.h
@@ -8,3 +8,22 @@
 #define MICROPY_HW_LED_ON(pin) (mp_hal_pin_low(pin))
 #define MICROPY_HW_LED_OFF(pin) (mp_hal_pin_high(pin))
 #define BOARD_FLASH_CONFIG_HEADER_H "evkmimxrt1050_flexspi_nor_config.h"
+
+// Define mapping logical UART # to hardware UART #
+// LPUART3 on D0/D1  -> 1
+// LPUART2 on D7/D6  -> 2
+// LPUART6 on D8/D9  -> 3
+// LPUART8 on A1/A0  -> 4
+
+#define MICROPY_HW_UART_NUM     (sizeof(uart_index_table) / sizeof(uart_index_table)[0])
+#define MICROPY_HW_UART_INDEX   { 0, 3, 2, 6, 8 }
+
+#define IOMUX_TABLE_UART \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B1_02_LPUART2_TX }, { IOMUXC_GPIO_AD_B1_03_LPUART2_RX }, \
+    { IOMUXC_GPIO_AD_B1_06_LPUART3_TX }, { IOMUXC_GPIO_AD_B1_07_LPUART3_RX }, \
+    { 0 }, { 0 }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B0_02_LPUART6_TX }, { IOMUXC_GPIO_AD_B0_03_LPUART6_RX }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B1_10_LPUART8_TX }, { IOMUXC_GPIO_AD_B1_11_LPUART8_RX },
diff --git a/ports/mimxrt/boards/MIMXRT1050_EVK/pins.csv b/ports/mimxrt/boards/MIMXRT1050_EVK/pins.csv
index afd63d4f9..366a141ff 100644
--- a/ports/mimxrt/boards/MIMXRT1050_EVK/pins.csv
+++ b/ports/mimxrt/boards/MIMXRT1050_EVK/pins.csv
@@ -29,23 +29,3 @@ SDI,GPIO_SD_B0_03
 SDO,GPIO_SD_B0_02
 CS,GPIO_SD_B0_01
 LED_GREEN,GPIO_AD_B0_09
-GPIO_AD_B1_07,GPIO_AD_B1_07
-GPIO_AD_B1_06,GPIO_AD_B1_06
-GPIO_AD_B0_11,GPIO_AD_B0_11
-GPIO_AD_B1_08,GPIO_AD_B1_08
-GPIO_AD_B0_09,GPIO_AD_B0_09
-GPIO_AD_B0_10,GPIO_AD_B0_10
-GPIO_AD_B1_02,GPIO_AD_B1_02
-GPIO_AD_B1_03,GPIO_AD_B1_03
-GPIO_AD_B0_03,GPIO_AD_B0_03
-GPIO_AD_B0_02,GPIO_AD_B0_02
-GPIO_SD_B0_01,GPIO_SD_B0_01
-GPIO_SD_B0_02,GPIO_SD_B0_02
-GPIO_SD_B0_03,GPIO_SD_B0_03
-GPIO_SD_B0_00,GPIO_SD_B0_00
-GPIO_AD_B1_01,GPIO_AD_B1_01
-GPIO_AD_B1_00,GPIO_AD_B1_00
-GPIO_AD_B1_10,GPIO_AD_B1_10
-GPIO_AD_B1_11,GPIO_AD_B1_11
-GPIO_AD_B1_04,GPIO_AD_B1_04
-GPIO_AD_B1_05,GPIO_AD_B1_05
diff --git a/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.h b/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.h
index 3974f9325..02372a3c5 100644
--- a/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.h
+++ b/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.h
@@ -8,3 +8,22 @@
 #define MICROPY_HW_LED_ON(pin) (mp_hal_pin_low(pin))
 #define MICROPY_HW_LED_OFF(pin) (mp_hal_pin_high(pin))
 #define BOARD_FLASH_CONFIG_HEADER_H "evkmimxrt1060_flexspi_nor_config.h"
+
+// Define mapping logical UART # to hardware UART #
+// LPUART3 on D0/D1  -> 1
+// LPUART2 on D7/D6  -> 2
+// LPUART6 on D8/D9  -> 3
+// LPUART8 on A1/A0  -> 4
+
+#define MICROPY_HW_UART_NUM     (sizeof(uart_index_table) / sizeof(uart_index_table)[0])
+#define MICROPY_HW_UART_INDEX   { 0, 3, 2, 6, 8 }
+
+#define IOMUX_TABLE_UART \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B1_02_LPUART2_TX }, { IOMUXC_GPIO_AD_B1_03_LPUART2_RX }, \
+    { IOMUXC_GPIO_AD_B1_06_LPUART3_TX }, { IOMUXC_GPIO_AD_B1_07_LPUART3_RX }, \
+    { 0 }, { 0 }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B0_02_LPUART6_TX }, { IOMUXC_GPIO_AD_B0_03_LPUART6_RX }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B1_10_LPUART8_TX }, { IOMUXC_GPIO_AD_B1_11_LPUART8_RX },
diff --git a/ports/mimxrt/boards/MIMXRT1060_EVK/pins.csv b/ports/mimxrt/boards/MIMXRT1060_EVK/pins.csv
index afd63d4f9..366a141ff 100644
--- a/ports/mimxrt/boards/MIMXRT1060_EVK/pins.csv
+++ b/ports/mimxrt/boards/MIMXRT1060_EVK/pins.csv
@@ -29,23 +29,3 @@ SDI,GPIO_SD_B0_03
 SDO,GPIO_SD_B0_02
 CS,GPIO_SD_B0_01
 LED_GREEN,GPIO_AD_B0_09
-GPIO_AD_B1_07,GPIO_AD_B1_07
-GPIO_AD_B1_06,GPIO_AD_B1_06
-GPIO_AD_B0_11,GPIO_AD_B0_11
-GPIO_AD_B1_08,GPIO_AD_B1_08
-GPIO_AD_B0_09,GPIO_AD_B0_09
-GPIO_AD_B0_10,GPIO_AD_B0_10
-GPIO_AD_B1_02,GPIO_AD_B1_02
-GPIO_AD_B1_03,GPIO_AD_B1_03
-GPIO_AD_B0_03,GPIO_AD_B0_03
-GPIO_AD_B0_02,GPIO_AD_B0_02
-GPIO_SD_B0_01,GPIO_SD_B0_01
-GPIO_SD_B0_02,GPIO_SD_B0_02
-GPIO_SD_B0_03,GPIO_SD_B0_03
-GPIO_SD_B0_00,GPIO_SD_B0_00
-GPIO_AD_B1_01,GPIO_AD_B1_01
-GPIO_AD_B1_00,GPIO_AD_B1_00
-GPIO_AD_B1_10,GPIO_AD_B1_10
-GPIO_AD_B1_11,GPIO_AD_B1_11
-GPIO_AD_B1_04,GPIO_AD_B1_04
-GPIO_AD_B1_05,GPIO_AD_B1_05
diff --git a/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.h b/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.h
index 01e2e10bb..e8492c922 100644
--- a/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.h
+++ b/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.h
@@ -1,9 +1,27 @@
 #define MICROPY_HW_BOARD_NAME "i.MX RT1064 EVK"
 #define MICROPY_HW_MCU_NAME   "MIMXRT1064DVL6A"
 
-
 // MIMXRT1064_EVK has 1 user LED
 #define MICROPY_HW_LED1_PIN (pin_GPIO_AD_B0_09)
 #define MICROPY_HW_LED_ON(pin) (mp_hal_pin_low(pin))
 #define MICROPY_HW_LED_OFF(pin) (mp_hal_pin_high(pin))
 #define BOARD_FLASH_CONFIG_HEADER_H "evkmimxrt1064_flexspi_nor_config.h"
+
+// Define mapping logical UART # to hardware UART #
+// LPUART3 on D0/D1  -> 1
+// LPUART2 on D7/D6  -> 2
+// LPUART6 on D8/D9  -> 3
+// LPUART8 on A1/A0  -> 4
+
+#define MICROPY_HW_UART_NUM     (sizeof(uart_index_table) / sizeof(uart_index_table)[0])
+#define MICROPY_HW_UART_INDEX   { 0, 3, 2, 6, 8 }
+
+#define IOMUX_TABLE_UART \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B1_02_LPUART2_TX }, { IOMUXC_GPIO_AD_B1_03_LPUART2_RX }, \
+    { IOMUXC_GPIO_AD_B1_06_LPUART3_TX }, { IOMUXC_GPIO_AD_B1_07_LPUART3_RX }, \
+    { 0 }, { 0 }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B0_02_LPUART6_TX }, { IOMUXC_GPIO_AD_B0_03_LPUART6_RX }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B1_10_LPUART8_TX }, { IOMUXC_GPIO_AD_B1_11_LPUART8_RX },
diff --git a/ports/mimxrt/boards/MIMXRT1064_EVK/pins.csv b/ports/mimxrt/boards/MIMXRT1064_EVK/pins.csv
index afd63d4f9..366a141ff 100644
--- a/ports/mimxrt/boards/MIMXRT1064_EVK/pins.csv
+++ b/ports/mimxrt/boards/MIMXRT1064_EVK/pins.csv
@@ -29,23 +29,3 @@ SDI,GPIO_SD_B0_03
 SDO,GPIO_SD_B0_02
 CS,GPIO_SD_B0_01
 LED_GREEN,GPIO_AD_B0_09
-GPIO_AD_B1_07,GPIO_AD_B1_07
-GPIO_AD_B1_06,GPIO_AD_B1_06
-GPIO_AD_B0_11,GPIO_AD_B0_11
-GPIO_AD_B1_08,GPIO_AD_B1_08
-GPIO_AD_B0_09,GPIO_AD_B0_09
-GPIO_AD_B0_10,GPIO_AD_B0_10
-GPIO_AD_B1_02,GPIO_AD_B1_02
-GPIO_AD_B1_03,GPIO_AD_B1_03
-GPIO_AD_B0_03,GPIO_AD_B0_03
-GPIO_AD_B0_02,GPIO_AD_B0_02
-GPIO_SD_B0_01,GPIO_SD_B0_01
-GPIO_SD_B0_02,GPIO_SD_B0_02
-GPIO_SD_B0_03,GPIO_SD_B0_03
-GPIO_SD_B0_00,GPIO_SD_B0_00
-GPIO_AD_B1_01,GPIO_AD_B1_01
-GPIO_AD_B1_00,GPIO_AD_B1_00
-GPIO_AD_B1_10,GPIO_AD_B1_10
-GPIO_AD_B1_11,GPIO_AD_B1_11
-GPIO_AD_B1_04,GPIO_AD_B1_04
-GPIO_AD_B1_05,GPIO_AD_B1_05
diff --git a/ports/mimxrt/boards/TEENSY40/mpconfigboard.h b/ports/mimxrt/boards/TEENSY40/mpconfigboard.h
index c6f11b51d..6bbac0a97 100644
--- a/ports/mimxrt/boards/TEENSY40/mpconfigboard.h
+++ b/ports/mimxrt/boards/TEENSY40/mpconfigboard.h
@@ -8,3 +8,17 @@
 #define MICROPY_HW_LED_ON(pin) (mp_hal_pin_high(pin))
 #define MICROPY_HW_LED_OFF(pin) (mp_hal_pin_low(pin))
 #define BOARD_FLASH_CONFIG_HEADER_H "teensy40_flexspi_nor_config.h"
+
+// UART config: 7 UARTs at the pins for Teensy 4.0
+#define MICROPY_HW_UART_NUM     (sizeof(uart_index_table) / sizeof(uart_index_table)[0])
+#define MICROPY_HW_UART_INDEX   { 0, 6, 4, 2, 3, 8, 1, 7 }
+
+#define IOMUX_TABLE_UART \
+    { IOMUXC_GPIO_AD_B0_12_LPUART1_TX }, { IOMUXC_GPIO_AD_B0_13_LPUART1_RX }, \
+    { IOMUXC_GPIO_AD_B1_02_LPUART2_TX }, { IOMUXC_GPIO_AD_B1_03_LPUART2_RX }, \
+    { IOMUXC_GPIO_AD_B1_06_LPUART3_TX }, { IOMUXC_GPIO_AD_B1_07_LPUART3_RX }, \
+    { IOMUXC_GPIO_B1_00_LPUART4_TX }, { IOMUXC_GPIO_B1_01_LPUART4_RX }, \
+    { 0 }, { 0 }, \
+    { IOMUXC_GPIO_AD_B0_02_LPUART6_TX }, { IOMUXC_GPIO_AD_B0_03_LPUART6_RX }, \
+    { IOMUXC_GPIO_EMC_31_LPUART7_TX }, { IOMUXC_GPIO_EMC_32_LPUART7_RX }, \
+    { IOMUXC_GPIO_AD_B1_10_LPUART8_TX }, { IOMUXC_GPIO_AD_B1_11_LPUART8_RX },
diff --git a/ports/mimxrt/boards/TEENSY41/mpconfigboard.h b/ports/mimxrt/boards/TEENSY41/mpconfigboard.h
index 6acfa11cd..1e07cb29c 100755
--- a/ports/mimxrt/boards/TEENSY41/mpconfigboard.h
+++ b/ports/mimxrt/boards/TEENSY41/mpconfigboard.h
@@ -8,3 +8,17 @@
 #define MICROPY_HW_LED_ON(pin) (mp_hal_pin_high(pin))
 #define MICROPY_HW_LED_OFF(pin) (mp_hal_pin_low(pin))
 #define BOARD_FLASH_CONFIG_HEADER_H "teensy41_flexspi_nor_config.h"
+
+// UART config: 8 UARTs at the pins for Teensy 4.1
+#define MICROPY_HW_UART_NUM     (sizeof(uart_index_table) / sizeof(uart_index_table)[0])
+#define MICROPY_HW_UART_INDEX   { 0, 6, 4, 2, 3, 8, 1, 7, 5 }
+
+#define IOMUX_TABLE_UART \
+    { IOMUXC_GPIO_AD_B0_12_LPUART1_TX }, { IOMUXC_GPIO_AD_B0_13_LPUART1_RX }, \
+    { IOMUXC_GPIO_AD_B1_02_LPUART2_TX }, { IOMUXC_GPIO_AD_B1_03_LPUART2_RX }, \
+    { IOMUXC_GPIO_AD_B1_06_LPUART3_TX }, { IOMUXC_GPIO_AD_B1_07_LPUART3_RX }, \
+    { IOMUXC_GPIO_B1_00_LPUART4_TX }, { IOMUXC_GPIO_B1_01_LPUART4_RX }, \
+    { IOMUXC_GPIO_B1_12_LPUART5_TX }, { IOMUXC_GPIO_B1_13_LPUART5_RX }, \
+    { IOMUXC_GPIO_AD_B0_02_LPUART6_TX }, { IOMUXC_GPIO_AD_B0_03_LPUART6_RX }, \
+    { IOMUXC_GPIO_EMC_31_LPUART7_TX }, { IOMUXC_GPIO_EMC_32_LPUART7_RX }, \
+    { IOMUXC_GPIO_AD_B1_10_LPUART8_TX }, { IOMUXC_GPIO_AD_B1_11_LPUART8_RX },
diff --git a/ports/mimxrt/machine_uart.c b/ports/mimxrt/machine_uart.c
new file mode 100644
index 000000000..abdb7ed97
--- /dev/null
+++ b/ports/mimxrt/machine_uart.c
@@ -0,0 +1,465 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020-2021 Damien P. George
+ * Copyright (c) 2021 Robert Hammelrath
+ *
+ * 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 "py/runtime.h"
+#include "py/stream.h"
+#include "py/mphal.h"
+#include "ticks.h"
+#include "fsl_common.h"
+#include "fsl_lpuart.h"
+#include "fsl_iomuxc.h"
+
+#define DEFAULT_UART_BAUDRATE (115200)
+#define DEFAULT_BUFFER_SIZE (256)
+#define MIN_BUFFER_SIZE  (32)
+#define MAX_BUFFER_SIZE  (32766)
+
+#define UART_INVERT_TX (1)
+#define UART_INVERT_RX (2)
+#define UART_INVERT_MASK (UART_INVERT_TX | UART_INVERT_RX)
+
+typedef struct _machine_uart_obj_t {
+    mp_obj_base_t base;
+    struct _lpuart_handle handle;
+    lpuart_config_t config;
+    LPUART_Type *lpuart;
+    uint16_t timeout;       // timeout waiting for first char (in ms)
+    uint16_t timeout_char;  // timeout waiting between chars (in ms)
+    uint8_t id;
+    uint8_t invert;
+    uint16_t tx_status;
+    uint8_t *txbuf;
+    uint16_t txbuf_len;
+    bool new;
+} machine_uart_obj_t;
+
+typedef struct _iomux_table_t {
+    uint32_t muxRegister;
+    uint32_t muxMode;
+    uint32_t inputRegister;
+    uint32_t inputDaisy;
+    uint32_t configRegister;
+} iomux_table_t;
+
+extern const mp_obj_type_t machine_uart_type;
+
+STATIC const uint8_t uart_index_table[] = MICROPY_HW_UART_INDEX;
+STATIC LPUART_Type *uart_base_ptr_table[] = LPUART_BASE_PTRS;
+static const iomux_table_t iomux_table_uart[] = {
+    IOMUX_TABLE_UART
+};
+
+STATIC const char *_parity_name[] = {"None", "", "0", "1"};  // Is defined as 0, 2, 3
+STATIC const char *_invert_name[] = {"None", "INV_TX", "INV_RX", "INV_TX|INV_RX"};
+
+#define RX (iomux_table_uart[index + 1])
+#define TX (iomux_table_uart[index])
+
+bool lpuart_set_iomux(int8_t uart) {
+    int index = (uart - 1) * 2;
+
+    if (TX.muxRegister != 0) {
+        IOMUXC_SetPinMux(TX.muxRegister, TX.muxMode, TX.inputRegister, TX.inputDaisy, TX.configRegister, 0U);
+        IOMUXC_SetPinConfig(TX.muxRegister, TX.muxMode, TX.inputRegister, TX.inputDaisy, TX.configRegister, 0x10B0u);
+
+        IOMUXC_SetPinMux(RX.muxRegister, RX.muxMode, RX.inputRegister, RX.inputDaisy, RX.configRegister, 0U);
+        IOMUXC_SetPinConfig(RX.muxRegister, RX.muxMode, RX.inputRegister, RX.inputDaisy, RX.configRegister, 0x10B0u);
+        return true;
+    } else {
+        return false;
+    }
+}
+
+uint32_t UART_SrcFreq(void) {
+    uint32_t freq;
+    // To make it simple, we assume default PLL and divider settings, and the
+    // only variable from application is use PLL3 source or OSC source.
+    if (CLOCK_GetMux(kCLOCK_UartMux) == 0) { // PLL3 div6 80M
+        freq = (CLOCK_GetPllFreq(kCLOCK_PllUsb1) / 6U) / (CLOCK_GetDiv(kCLOCK_UartDiv) + 1U);
+    } else {
+        freq = CLOCK_GetOscFreq() / (CLOCK_GetDiv(kCLOCK_UartDiv) + 1U);
+    }
+    return freq;
+}
+
+void LPUART_UserCallback(LPUART_Type *base, lpuart_handle_t *handle, status_t status, void *userData) {
+    machine_uart_obj_t *self = userData;
+    if (kStatus_LPUART_TxIdle == status) {
+        self->tx_status = kStatus_LPUART_TxIdle;
+    }
+
+    if (kStatus_LPUART_RxRingBufferOverrun == status) {
+        ; // Ringbuffer full, deassert RTS if flow control is enabled
+    }
+}
+
+STATIC void machine_uart_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
+    machine_uart_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_printf(print, "UART(%u, baudrate=%u, bits=%u, parity=%s, stop=%u, "
+        "rxbuf=%d, txbuf=%d, timeout=%u, timeout_char=%u, invert=%s)",
+        self->id, self->config.baudRate_Bps, 8 - self->config.dataBitsCount,
+        _parity_name[self->config.parityMode], self->config.stopBitCount + 1,
+        self->handle.rxRingBufferSize, self->txbuf_len, self->timeout, self->timeout_char,
+        _invert_name[self->invert]);
+}
+
+STATIC mp_obj_t machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    enum { ARG_baudrate, ARG_bits, ARG_parity, ARG_stop,
+           ARG_timeout, ARG_timeout_char, ARG_invert, ARG_rxbuf, ARG_txbuf};
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_baudrate, MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_bits, MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_parity, MP_ARG_OBJ, {.u_rom_obj = MP_ROM_INT(-1)} },
+        { MP_QSTR_stop, MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_timeout_char, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_invert, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_rxbuf, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_txbuf, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
+    };
+
+    // Parse args
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    // Set baudrate if configured.
+    if (args[ARG_baudrate].u_int > 0) {
+        self->config.baudRate_Bps = args[ARG_baudrate].u_int;
+    }
+
+    // Set bits if configured.
+    if (args[ARG_bits].u_int > 0) {
+        self->config.dataBitsCount = 8 - args[ARG_bits].u_int;
+    }
+
+    // Set parity if configured.
+    if (args[ARG_parity].u_obj != MP_OBJ_NEW_SMALL_INT(-1)) {
+        if (args[ARG_parity].u_obj == mp_const_none) {
+            self->config.parityMode = kLPUART_ParityDisabled;
+        } else if (mp_obj_get_int(args[ARG_parity].u_obj) & 1) {
+            self->config.parityMode = kLPUART_ParityOdd;
+        } else {
+            self->config.parityMode = kLPUART_ParityEven;
+        }
+    }
+
+    // Set stop bits if configured.
+    if (args[ARG_stop].u_int > 0) {
+        self->config.stopBitCount = args[ARG_stop].u_int - 1;
+    }
+
+    // Set timeout if configured.
+    if (args[ARG_timeout].u_int >= 0) {
+        self->timeout = args[ARG_timeout].u_int;
+    }
+
+    // Set timeout_char if configured.
+    if (args[ARG_timeout_char].u_int >= 0) {
+        self->timeout_char = args[ARG_timeout_char].u_int;
+    }
+
+    // Set line inversion if configured.
+    if (args[ARG_invert].u_int >= 0) {
+        if (args[ARG_invert].u_int & ~UART_INVERT_MASK) {
+            mp_raise_ValueError(MP_ERROR_TEXT("bad inversion mask"));
+        }
+        self->invert = args[ARG_invert].u_int;
+    }
+
+    self->tx_status = kStatus_LPUART_TxIdle;
+    self->config.enableTx = true;
+    self->config.enableRx = true;
+
+    // Set the RX buffer size if configured.
+    size_t rxbuf_len = DEFAULT_BUFFER_SIZE;
+    if (args[ARG_rxbuf].u_int > 0) {
+        rxbuf_len = args[ARG_rxbuf].u_int;
+        if (rxbuf_len < MIN_BUFFER_SIZE) {
+            rxbuf_len = MIN_BUFFER_SIZE;
+        } else if (rxbuf_len > MAX_BUFFER_SIZE) {
+            mp_raise_ValueError(MP_ERROR_TEXT("rxbuf too large"));
+        }
+    }
+
+    // Set the TX buffer size if configured.
+    size_t txbuf_len = DEFAULT_BUFFER_SIZE;
+    if (args[ARG_txbuf].u_int > 0) {
+        txbuf_len = args[ARG_txbuf].u_int;
+        if (txbuf_len < MIN_BUFFER_SIZE) {
+            txbuf_len = MIN_BUFFER_SIZE;
+        } else if (txbuf_len > MAX_BUFFER_SIZE) {
+            mp_raise_ValueError(MP_ERROR_TEXT("txbuf too large"));
+        }
+    }
+
+    // Initialise the UART peripheral if any arguments given, or it was not initialised previously.
+    if (n_args > 1 || self->new) {
+        self->new = false;
+        // may be obsolete
+        if (self->config.baudRate_Bps == 0) {
+            self->config.baudRate_Bps = DEFAULT_UART_BAUDRATE;
+        }
+
+        // Make sure timeout_char is at least as long as a whole character (13 bits to be safe).
+        uint32_t min_timeout_char = 13000 / self->config.baudRate_Bps + 1;
+        if (self->timeout_char < min_timeout_char) {
+            self->timeout_char = min_timeout_char;
+        }
+
+        LPUART_Init(self->lpuart, &self->config, UART_SrcFreq()); // ??
+        LPUART_TransferCreateHandle(self->lpuart, &self->handle,  LPUART_UserCallback, self);
+        uint8_t *buffer = m_new(uint8_t, rxbuf_len + 1);
+        LPUART_TransferStartRingBuffer(self->lpuart, &self->handle, buffer, rxbuf_len);
+        self->txbuf = m_new(uint8_t, txbuf_len); // Allocate the TX buffer.
+        self->txbuf_len = txbuf_len;
+
+        // The Uart supports inverting, but not the fsl API, so it has to coded directly
+        // And it has to be done after LPUART_Init.
+        if (self->invert & UART_INVERT_RX) {
+            LPUART_EnableRx(self->lpuart, false);
+            self->lpuart->STAT |= 1 << LPUART_STAT_RXINV_SHIFT;
+            LPUART_EnableRx(self->lpuart, true);
+        }
+        if (self->invert & UART_INVERT_TX) {
+            LPUART_EnableTx(self->lpuart, false);
+            self->lpuart->CTRL |= 1 << LPUART_CTRL_TXINV_SHIFT;
+            LPUART_EnableTx(self->lpuart, true);
+        }
+        // Send long break; drop that code for a shorter break duration
+        LPUART_EnableTx(self->lpuart, false);
+        self->lpuart->STAT |= 1 << LPUART_STAT_BRK13_SHIFT;
+        LPUART_EnableTx(self->lpuart, true);
+
+        // Allocate the TX ring buffer. Not used yet, but maybe later.
+
+        // ringbuf_alloc(&(self->write_buffer), txbuf_len + 1);
+        // MP_STATE_PORT(rp2_uart_tx_buffer[uart_id]) = self->write_buffer.buf;
+
+    }
+
+    return MP_OBJ_FROM_PTR(self);
+}
+
+STATIC mp_obj_t machine_uart_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    mp_arg_check_num(n_args, n_kw, 1, MP_OBJ_FUN_ARGS_MAX, true);
+
+    // Get UART bus.
+    int uart_id = mp_obj_get_int(args[0]);
+    if (uart_id < 1 || uart_id > MICROPY_HW_UART_NUM) {
+        mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("UART(%d) doesn't exist"), uart_id);
+    }
+
+    // Create the UART object and fill it with defaults.
+    uint8_t uart_hw_id = uart_index_table[uart_id];  // the hw uart number 1..n
+    machine_uart_obj_t *self = m_new_obj(machine_uart_obj_t);
+    self->base.type = &machine_uart_type;
+    self->id = uart_id;
+    self->lpuart = uart_base_ptr_table[uart_hw_id];
+    self->invert = false;
+    self->timeout = 1;
+    self->timeout_char = 1;
+    self->new = true;
+    LPUART_GetDefaultConfig(&self->config);
+
+    // Configure board-specific pin MUX based on the hardware device number.
+    lpuart_set_iomux(uart_hw_id);
+
+    mp_map_t kw_args;
+    mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
+    return machine_uart_init_helper(self, n_args - 1, args + 1, &kw_args);
+}
+
+// uart.init(baud, [kwargs])
+STATIC mp_obj_t machine_uart_init(size_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
+    return machine_uart_init_helper(args[0], n_args - 1, args + 1, kw_args);
+}
+MP_DEFINE_CONST_FUN_OBJ_KW(machine_uart_init_obj, 1, machine_uart_init);
+
+STATIC mp_obj_t machine_uart_any(mp_obj_t self_in) {
+    machine_uart_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    size_t count = LPUART_TransferGetRxRingBufferLength(self->lpuart, &self->handle);
+    return MP_OBJ_NEW_SMALL_INT(count);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(machine_uart_any_obj, machine_uart_any);
+
+STATIC mp_obj_t machine_uart_sendbreak(mp_obj_t self_in) {
+    machine_uart_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    self->lpuart->CTRL |= 1 << LPUART_CTRL_SBK_SHIFT; // Set SBK bit
+    self->lpuart->CTRL &= ~LPUART_CTRL_SBK_MASK; // Clear SBK bit
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(machine_uart_sendbreak_obj, machine_uart_sendbreak);
+
+STATIC const mp_rom_map_elem_t machine_uart_locals_dict_table[] = {
+    { MP_ROM_QSTR(MP_QSTR_init), MP_ROM_PTR(&machine_uart_init_obj) },
+
+    { MP_ROM_QSTR(MP_QSTR_any), MP_ROM_PTR(&machine_uart_any_obj) },
+
+    { MP_ROM_QSTR(MP_QSTR_read), MP_ROM_PTR(&mp_stream_read_obj) },
+    { MP_ROM_QSTR(MP_QSTR_readline), MP_ROM_PTR(&mp_stream_unbuffered_readline_obj) },
+    { MP_ROM_QSTR(MP_QSTR_readinto), MP_ROM_PTR(&mp_stream_readinto_obj) },
+    { MP_ROM_QSTR(MP_QSTR_write), MP_ROM_PTR(&mp_stream_write_obj) },
+
+    { MP_ROM_QSTR(MP_QSTR_sendbreak), MP_ROM_PTR(&machine_uart_sendbreak_obj) },
+
+    { MP_ROM_QSTR(MP_QSTR_INV_TX), MP_ROM_INT(UART_INVERT_TX) },
+    { MP_ROM_QSTR(MP_QSTR_INV_RX), MP_ROM_INT(UART_INVERT_RX) },
+
+};
+STATIC MP_DEFINE_CONST_DICT(machine_uart_locals_dict, machine_uart_locals_dict_table);
+
+STATIC mp_uint_t machine_uart_read(mp_obj_t self_in, void *buf_in, mp_uint_t size, int *errcode) {
+    machine_uart_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    uint64_t t = ticks_us64() + (uint64_t)self->timeout * 1000;
+    uint64_t timeout_char_us = (uint64_t)self->timeout_char * 1000;
+    lpuart_transfer_t xfer;
+    uint8_t *dest = buf_in;
+    size_t avail;
+    size_t nget;
+
+    for (size_t received = 0; received < size;) {
+        // Wait for the first/next character.
+        while ((avail = LPUART_TransferGetRxRingBufferLength(self->lpuart, &self->handle)) <= 0) {
+            if (ticks_us64() > t) { // timed out
+                if (received <= 0) {
+                    *errcode = MP_EAGAIN;
+                    return MP_STREAM_ERROR;
+                } else {
+                    return received;
+                }
+            }
+            MICROPY_EVENT_POLL_HOOK
+        }
+        // Get as many bytes as possible to meet the need.
+        nget = avail < (size - received) ? avail : size - received;
+        xfer.data = dest + received;
+        xfer.dataSize = nget;
+        LPUART_TransferReceiveNonBlocking(self->lpuart, &self->handle, &xfer, NULL);
+        received += nget;
+        t = ticks_us64() + timeout_char_us;
+    }
+    return size;
+}
+
+STATIC mp_uint_t machine_uart_write(mp_obj_t self_in, const void *buf_in, mp_uint_t size, int *errcode) {
+    machine_uart_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    lpuart_transfer_t xfer;
+    uint64_t t;
+    size_t remaining = size;
+    size_t offset = 0;
+    uint8_t fifo_size = FSL_FEATURE_LPUART_FIFO_SIZEn(0);
+
+    // First check if a previous transfer is still ongoing,
+    // then wait at least the number of remaining character times.
+    t = ticks_us64() + (uint64_t)(self->handle.txDataSize + fifo_size) * (13000000 / self->config.baudRate_Bps + 1000);
+    while (self->tx_status != kStatus_LPUART_TxIdle) {
+        if (ticks_us64() > t) { // timed out, hard error
+            *errcode = MP_ETIMEDOUT;
+            return MP_STREAM_ERROR;
+        }
+        MICROPY_EVENT_POLL_HOOK
+    }
+
+    // Check if the first part has to be sent semi-blocking.
+    if (size > self->txbuf_len) {
+        // Send the first block.
+        xfer.data = (uint8_t *)buf_in;
+        offset = xfer.dataSize = size - self->txbuf_len;
+        self->tx_status = kStatus_LPUART_TxBusy;
+        LPUART_TransferSendNonBlocking(self->lpuart, &self->handle, &xfer);
+
+        // Wait at least the number of character times for this chunk.
+        t = ticks_us64() + (uint64_t)xfer.dataSize * (13000000 / self->config.baudRate_Bps + 1000);
+        while (self->handle.txDataSize) {
+            // Wait for the first/next character to be sent.
+            if (ticks_us64() > t) { // timed out
+                if (self->handle.txDataSize >= size) {
+                    *errcode = MP_ETIMEDOUT;
+                    return MP_STREAM_ERROR;
+                } else {
+                    return size - self->handle.txDataSize;
+                }
+            }
+            MICROPY_EVENT_POLL_HOOK
+        }
+        remaining = self->txbuf_len;
+    } else {
+        // The data fits into the tx buffer.
+        offset = 0;
+        remaining = size;
+    }
+
+    // Send the remaining data without waiting for completion.
+    memcpy(self->txbuf, (uint8_t *)buf_in + offset, remaining);
+    xfer.data = self->txbuf;
+    xfer.dataSize = remaining;
+    self->tx_status = kStatus_LPUART_TxBusy;
+    LPUART_TransferSendNonBlocking(self->lpuart, &self->handle, &xfer);
+
+    return size;
+}
+
+STATIC mp_uint_t machine_uart_ioctl(mp_obj_t self_in, mp_uint_t request, mp_uint_t arg, int *errcode) {
+    machine_uart_obj_t *self = self_in;
+    mp_uint_t ret;
+    if (request == MP_STREAM_POLL) {
+        uintptr_t flags = arg;
+        ret = 0;
+        if (flags & MP_STREAM_POLL_RD) {
+            uint32_t count;
+            count = LPUART_TransferGetRxRingBufferLength(self->lpuart, &self->handle);
+            if (count > 0) {
+                ret |= MP_STREAM_POLL_RD;
+            }
+        }
+        if ((flags & MP_STREAM_POLL_WR)) {
+            ret |= MP_STREAM_POLL_WR;
+        }
+    } else {
+        *errcode = MP_EINVAL;
+        ret = MP_STREAM_ERROR;
+    }
+    return ret;
+}
+
+STATIC const mp_stream_p_t uart_stream_p = {
+    .read = machine_uart_read,
+    .write = machine_uart_write,
+    .ioctl = machine_uart_ioctl,
+    .is_text = false,
+};
+
+const mp_obj_type_t machine_uart_type = {
+    { &mp_type_type },
+    .name = MP_QSTR_UART,
+    .print = machine_uart_print,
+    .make_new = machine_uart_make_new,
+    .getiter = mp_identity_getiter,
+    .iternext = mp_stream_unbuffered_iter,
+    .protocol = &uart_stream_p,
+    .locals_dict = (mp_obj_dict_t *)&machine_uart_locals_dict,
+};
diff --git a/ports/mimxrt/modmachine.c b/ports/mimxrt/modmachine.c
index dfee91992..09aa250c5 100644
--- a/ports/mimxrt/modmachine.c
+++ b/ports/mimxrt/modmachine.c
@@ -65,6 +65,7 @@ STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_Signal),              MP_ROM_PTR(&machine_signal_type) },
     { MP_ROM_QSTR(MP_QSTR_SoftI2C),             MP_ROM_PTR(&mp_machine_soft_i2c_type) },
     { MP_ROM_QSTR(MP_QSTR_SoftSPI),             MP_ROM_PTR(&mp_machine_soft_spi_type) },
+    { MP_ROM_QSTR(MP_QSTR_UART),                MP_ROM_PTR(&machine_uart_type) },
 };
 STATIC MP_DEFINE_CONST_DICT(machine_module_globals, machine_module_globals_table);
 
diff --git a/ports/mimxrt/modmachine.h b/ports/mimxrt/modmachine.h
index a7b577fa7..0b9e89cb2 100644
--- a/ports/mimxrt/modmachine.h
+++ b/ports/mimxrt/modmachine.h
@@ -32,6 +32,7 @@
 extern const mp_obj_type_t machine_adc_type;
 extern const mp_obj_type_t machine_timer_type;
 extern const mp_obj_type_t machine_rtc_type;
+extern const mp_obj_type_t machine_uart_type;
 
 void machine_adc_init(void);
 void machine_timer_init_PIT(void);