mbed library sources. Supersedes mbed-src.

Dependents:   Nucleo_Hello_Encoder BLE_iBeaconScan AM1805_DEMO DISCO-F429ZI_ExportTemplate1 ... more

Revision:
187:0387e8f68319
Child:
188:bcfe06ba3d64
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/targets/TARGET_NUVOTON/TARGET_M2351/serial_api.c	Thu Sep 06 13:40:20 2018 +0100
@@ -0,0 +1,1174 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2017-2018 Nuvoton
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "serial_api.h"
+
+#if DEVICE_SERIAL
+
+#include "cmsis.h"
+#include "mbed_error.h"
+#include "mbed_assert.h"
+#include "PeripheralPins.h"
+#include "nu_modutil.h"
+#include "nu_bitutil.h"
+#include <string.h>
+
+#if DEVICE_SERIAL_ASYNCH
+#include "dma_api.h"
+#include "dma.h"
+#endif
+
+struct nu_uart_var {
+    uint32_t    ref_cnt;                // Reference count of the H/W module
+    serial_t *  obj;
+    uint32_t    fifo_size_tx;
+    uint32_t    fifo_size_rx;
+    void        (*vec)(void);
+#if DEVICE_SERIAL_ASYNCH
+    void        (*vec_async)(void);
+    uint8_t     pdma_perp_tx;
+    uint8_t     pdma_perp_rx;
+#endif
+};
+
+static void uart0_vec(void);
+static void uart1_vec(void);
+static void uart2_vec(void);
+static void uart3_vec(void);
+static void uart4_vec(void);
+static void uart5_vec(void);
+static void uart_irq(serial_t *obj);
+
+#if DEVICE_SERIAL_ASYNCH
+static void uart0_vec_async(void);
+static void uart1_vec_async(void);
+static void uart2_vec_async(void);
+static void uart3_vec_async(void);
+static void uart4_vec_async(void);
+static void uart5_vec_async(void);
+static void uart_irq_async(serial_t *obj);
+
+static void uart_dma_handler_tx(uint32_t id, uint32_t event);
+static void uart_dma_handler_rx(uint32_t id, uint32_t event);
+
+static void serial_tx_enable_interrupt(serial_t *obj, uint32_t address, uint8_t enable);
+static void serial_rx_enable_interrupt(serial_t *obj, uint32_t address, uint8_t enable);
+static void serial_enable_interrupt(serial_t *obj, SerialIrq irq, uint32_t enable);
+static void serial_rollback_interrupt(serial_t *obj, SerialIrq irq);
+static int serial_write_async(serial_t *obj);
+static int serial_read_async(serial_t *obj);
+
+static uint32_t serial_rx_event_check(serial_t *obj);
+static uint32_t serial_tx_event_check(serial_t *obj);
+
+static int serial_is_tx_complete(serial_t *obj);
+static void serial_tx_enable_event(serial_t *obj, int event, uint8_t enable);
+
+static void serial_tx_buffer_set(serial_t *obj, const void *tx, size_t length, uint8_t width);
+static void serial_rx_buffer_set(serial_t *obj, void *rx, size_t length, uint8_t width);
+static void serial_rx_set_char_match(serial_t *obj, uint8_t char_match);
+static void serial_rx_enable_event(serial_t *obj, int event, uint8_t enable);
+static int serial_is_rx_complete(serial_t *obj);
+
+static void serial_check_dma_usage(DMAUsage *dma_usage, int *dma_ch);
+static int serial_is_irq_en(serial_t *obj, SerialIrq irq);
+#endif
+
+static struct nu_uart_var uart0_var = {
+    .ref_cnt            =   0,
+    .obj                =   NULL,
+    .fifo_size_tx       =   16,
+    .fifo_size_rx       =   16,
+    .vec                =   uart0_vec,
+#if DEVICE_SERIAL_ASYNCH
+    .vec_async          =   uart0_vec_async,
+    .pdma_perp_tx       =   PDMA_UART0_TX,
+    .pdma_perp_rx       =   PDMA_UART0_RX
+#endif
+};
+static struct nu_uart_var uart1_var = {
+    .ref_cnt            =   0,
+    .obj                =   NULL,
+    .fifo_size_tx       =   16,
+    .fifo_size_rx       =   16,
+    .vec                =   uart1_vec,
+#if DEVICE_SERIAL_ASYNCH
+    .vec_async          =   uart1_vec_async,
+    .pdma_perp_tx       =   PDMA_UART1_TX,
+    .pdma_perp_rx       =   PDMA_UART1_RX
+#endif
+};
+static struct nu_uart_var uart2_var = {
+    .ref_cnt            =   0,
+    .obj                =   NULL,
+    .fifo_size_tx       =   16,
+    .fifo_size_rx       =   16,
+    .vec                =   uart2_vec,
+#if DEVICE_SERIAL_ASYNCH
+    .vec_async          =   uart2_vec_async,
+    .pdma_perp_tx       =   PDMA_UART2_TX,
+    .pdma_perp_rx       =   PDMA_UART2_RX
+#endif
+};
+static struct nu_uart_var uart3_var = {
+    .ref_cnt            =   0,
+    .obj                =   NULL,
+    .fifo_size_tx       =   16,
+    .fifo_size_rx       =   16,
+    .vec                =   uart3_vec,
+#if DEVICE_SERIAL_ASYNCH
+    .vec_async          =   uart3_vec_async,
+    .pdma_perp_tx       =   PDMA_UART3_TX,
+    .pdma_perp_rx       =   PDMA_UART3_RX
+#endif
+};
+static struct nu_uart_var uart4_var = {
+    .ref_cnt            =   0,
+    .obj                =   NULL,
+    .fifo_size_tx       =   16,
+    .fifo_size_rx       =   16,
+    .vec                =   uart4_vec,
+#if DEVICE_SERIAL_ASYNCH
+    .vec_async          =   uart4_vec_async,
+    .pdma_perp_tx       =   PDMA_UART4_TX,
+    .pdma_perp_rx       =   PDMA_UART4_RX
+#endif
+};
+static struct nu_uart_var uart5_var = {
+    .ref_cnt            =   0,
+    .obj                =   NULL,
+    .fifo_size_tx       =   16,
+    .fifo_size_rx       =   16,
+    .vec                =   uart5_vec,
+#if DEVICE_SERIAL_ASYNCH
+    .vec_async          =   uart5_vec_async,
+    .pdma_perp_tx       =   PDMA_UART5_TX,
+    .pdma_perp_rx       =   PDMA_UART5_RX
+#endif
+};
+
+
+int stdio_uart_inited = 0;
+serial_t stdio_uart;
+static uint32_t uart_modinit_mask = 0;
+
+static const struct nu_modinit_s uart_modinit_tab[] = {
+    {UART_0, UART0_MODULE, CLK_CLKSEL1_UART0SEL_HIRC, CLK_CLKDIV0_UART0(1), UART0_RST, UART0_IRQn, &uart0_var},
+    {UART_1, UART1_MODULE, CLK_CLKSEL1_UART1SEL_HIRC, CLK_CLKDIV0_UART1(1), UART1_RST, UART1_IRQn, &uart1_var},
+    {UART_2, UART2_MODULE, CLK_CLKSEL3_UART2SEL_HIRC, CLK_CLKDIV4_UART2(1), UART2_RST, UART2_IRQn, &uart2_var},
+    {UART_3, UART3_MODULE, CLK_CLKSEL3_UART3SEL_HIRC, CLK_CLKDIV4_UART3(1), UART3_RST, UART3_IRQn, &uart3_var},
+    {UART_4, UART4_MODULE, CLK_CLKSEL3_UART4SEL_HIRC, CLK_CLKDIV4_UART4(1), UART4_RST, UART4_IRQn, &uart4_var},
+    {UART_5, UART5_MODULE, CLK_CLKSEL3_UART5SEL_HIRC, CLK_CLKDIV4_UART5(1), UART5_RST, UART5_IRQn, &uart5_var},
+
+    {NC, 0, 0, 0, 0, (IRQn_Type) 0, NULL}
+};
+
+extern void mbed_sdk_init(void);
+
+void serial_init(serial_t *obj, PinName tx, PinName rx)
+{
+    // NOTE: With armcc, serial_init() gets called from _sys_open() timing of which is before main()/mbed_sdk_init().
+    mbed_sdk_init();
+
+    // Determine which UART_x the pins are used for
+    uint32_t uart_tx = pinmap_peripheral(tx, PinMap_UART_TX);
+    uint32_t uart_rx = pinmap_peripheral(rx, PinMap_UART_RX);
+    // Get the peripheral name (UART_x) from the pins and assign it to the object
+    obj->serial.uart = (UARTName) pinmap_merge(uart_tx, uart_rx);
+    MBED_ASSERT((int)obj->serial.uart != NC);
+
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+
+    if (! var->ref_cnt) {
+        do {
+            /* Reset module
+             *
+             * NOTE: We must call secure version (from non-secure domain) because SYS/CLK regions are secure.
+             */
+            SYS_ResetModule_S(modinit->rsetidx);
+
+            /* Select IP clock source
+             *
+             * NOTE: We must call secure version (from non-secure domain) because SYS/CLK regions are secure.
+             */
+            CLK_SetModuleClock_S(modinit->clkidx, modinit->clksrc, modinit->clkdiv);
+            
+            /* Enable IP clock
+             *
+             * NOTE: We must call secure version (from non-secure domain) because SYS/CLK regions are secure.
+             */
+            CLK_EnableModuleClock_S(modinit->clkidx);
+
+            pinmap_pinout(tx, PinMap_UART_TX);
+            pinmap_pinout(rx, PinMap_UART_RX);
+        } while (0);
+
+        obj->serial.pin_tx = tx;
+        obj->serial.pin_rx = rx;
+    }
+    var->ref_cnt ++;
+
+    // Configure the UART module and set its baudrate
+    serial_baud(obj, 9600);
+    // Configure data bits, parity, and stop bits
+    serial_format(obj, 8, ParityNone, 1);
+
+    obj->serial.vec = var->vec;
+    obj->serial.irq_en = 0;
+
+#if DEVICE_SERIAL_ASYNCH
+    obj->serial.dma_usage_tx = DMA_USAGE_NEVER;
+    obj->serial.dma_usage_rx = DMA_USAGE_NEVER;
+    obj->serial.event = 0;
+    obj->serial.dma_chn_id_tx = DMA_ERROR_OUT_OF_CHANNELS;
+    obj->serial.dma_chn_id_rx = DMA_ERROR_OUT_OF_CHANNELS;
+#endif
+
+    // For stdio management
+    if (obj->serial.uart == STDIO_UART) {
+        stdio_uart_inited = 1;
+        memcpy(&stdio_uart, obj, sizeof(serial_t));
+    }
+
+    if (var->ref_cnt) {
+        // Mark this module to be inited.
+        int i = modinit - uart_modinit_tab;
+        uart_modinit_mask |= 1 << i;
+    }
+}
+
+void serial_free(serial_t *obj)
+{
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+
+    var->ref_cnt --;
+    if (! var->ref_cnt) {
+#if DEVICE_SERIAL_ASYNCH
+        if (obj->serial.dma_chn_id_tx != DMA_ERROR_OUT_OF_CHANNELS) {
+            dma_channel_free(obj->serial.dma_chn_id_tx);
+            obj->serial.dma_chn_id_tx = DMA_ERROR_OUT_OF_CHANNELS;
+        }
+        if (obj->serial.dma_chn_id_rx != DMA_ERROR_OUT_OF_CHANNELS) {
+            dma_channel_free(obj->serial.dma_chn_id_rx);
+            obj->serial.dma_chn_id_rx = DMA_ERROR_OUT_OF_CHANNELS;
+        }
+#endif
+
+        do {
+            UART_Close((UART_T *) NU_MODBASE(obj->serial.uart));
+
+            UART_DISABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), (UART_INTEN_RDAIEN_Msk | UART_INTEN_THREIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+            NVIC_DisableIRQ(modinit->irq_n);
+
+            /* Disable IP clock
+             *
+             * NOTE: We must call secure version (from non-secure domain) because SYS/CLK regions are secure.
+             */
+            CLK_DisableModuleClock_S(modinit->clkidx);
+        } while (0);
+    }
+
+    if (var->obj == obj) {
+        var->obj = NULL;
+    }
+
+    if (obj->serial.uart == STDIO_UART) {
+        stdio_uart_inited = 0;
+    }
+
+    if (! var->ref_cnt) {
+        // Mark this module to be deinited.
+        int i = modinit - uart_modinit_tab;
+        uart_modinit_mask &= ~(1 << i);
+    }
+}
+
+void serial_baud(serial_t *obj, int baudrate)
+{
+    // Flush Tx FIFO. Otherwise, output data may get lost on this change.
+    while (! UART_IS_TX_EMPTY((UART_T *) NU_MODBASE(obj->serial.uart)));
+
+    obj->serial.baudrate = baudrate;
+    UART_Open((UART_T *) NU_MODBASE(obj->serial.uart), baudrate);
+}
+
+void serial_format(serial_t *obj, int data_bits, SerialParity parity, int stop_bits)
+{
+    // Flush Tx FIFO. Otherwise, output data may get lost on this change.
+    while (! UART_IS_TX_EMPTY((UART_T *) NU_MODBASE(obj->serial.uart)));
+
+    // Sanity check arguments
+    MBED_ASSERT((data_bits == 5) || (data_bits == 6) || (data_bits == 7) || (data_bits == 8));
+    MBED_ASSERT((parity == ParityNone) || (parity == ParityOdd) || (parity == ParityEven) || (parity == ParityForced1) || (parity == ParityForced0));
+    MBED_ASSERT((stop_bits == 1) || (stop_bits == 2));
+
+    obj->serial.databits = data_bits;
+    obj->serial.parity = parity;
+    obj->serial.stopbits = stop_bits;
+
+    uint32_t databits_intern = (data_bits == 5) ? UART_WORD_LEN_5 :
+                               (data_bits == 6) ? UART_WORD_LEN_6 :
+                               (data_bits == 7) ? UART_WORD_LEN_7 :
+                               UART_WORD_LEN_8;
+    uint32_t parity_intern = (parity == ParityOdd || parity == ParityForced1) ? UART_PARITY_ODD :
+                             (parity == ParityEven || parity == ParityForced0) ? UART_PARITY_EVEN :
+                             UART_PARITY_NONE;
+    uint32_t stopbits_intern = (stop_bits == 2) ? UART_STOP_BIT_2 : UART_STOP_BIT_1;
+    UART_SetLineConfig((UART_T *) NU_MODBASE(obj->serial.uart),
+                        0,  // Don't change baudrate
+                        databits_intern,
+                        parity_intern,
+                        stopbits_intern);
+}
+
+#if DEVICE_SERIAL_FC
+
+void serial_set_flow_control(serial_t *obj, FlowControl type, PinName rxflow, PinName txflow)
+{
+    UART_T *uart_base = (UART_T *) NU_MODBASE(obj->serial.uart);
+
+    // First, disable flow control completely.
+    uart_base->INTEN &= ~(UART_INTEN_ATORTSEN_Msk | UART_INTEN_ATOCTSEN_Msk);
+
+    if ((type == FlowControlRTS || type == FlowControlRTSCTS) && rxflow != NC) {
+        // Check if RTS pin matches.
+        uint32_t uart_rts = pinmap_peripheral(rxflow, PinMap_UART_RTS);
+        MBED_ASSERT(uart_rts == obj->serial.uart);
+        // Enable the pin for RTS function
+        pinmap_pinout(rxflow, PinMap_UART_RTS);
+
+        // NOTE: Added in M480/M2351. Before configuring RTSACTLV, disable TX/RX.
+        uart_base->FUNCSEL |= UART_FUNCSEL_TXRXDIS_Msk;
+        while (uart_base->FIFOSTS & UART_FIFOSTS_TXRXACT_Msk);
+        // nRTS pin output is low level active
+        uart_base->MODEM |= UART_MODEM_RTSACTLV_Msk;
+        // NOTE: Added in M480/M2351. After configuring RTSACTLV, re-enable TX/RX.
+        uart_base->FUNCSEL &= ~UART_FUNCSEL_TXRXDIS_Msk;
+
+        uart_base->FIFO = (uart_base->FIFO & ~UART_FIFO_RTSTRGLV_Msk) | UART_FIFO_RTSTRGLV_8BYTES;
+
+        // Enable RTS
+        uart_base->INTEN |= UART_INTEN_ATORTSEN_Msk;
+    }
+
+    if ((type == FlowControlCTS || type == FlowControlRTSCTS) && txflow != NC)  {
+        // Check if CTS pin matches.
+        uint32_t uart_cts = pinmap_peripheral(txflow, PinMap_UART_CTS);
+        MBED_ASSERT(uart_cts == obj->serial.uart);
+        // Enable the pin for CTS function
+        pinmap_pinout(txflow, PinMap_UART_CTS);
+
+        // NOTE: Added in M480/M2351. Before configuring CTSACTLV, disable TX/RX.
+        uart_base->FUNCSEL |= UART_FUNCSEL_TXRXDIS_Msk;
+        while (uart_base->FIFOSTS & UART_FIFOSTS_TXRXACT_Msk);
+        // nCTS pin input is low level active
+        uart_base->MODEMSTS |= UART_MODEMSTS_CTSACTLV_Msk;
+        // NOTE: Added in M480/M2351. After configuring CTSACTLV, re-enable TX/RX.
+        uart_base->FUNCSEL &= ~UART_FUNCSEL_TXRXDIS_Msk;
+
+        // Enable CTS
+        uart_base->INTEN |= UART_INTEN_ATOCTSEN_Msk;
+    }
+}
+
+#endif  //DEVICE_SERIAL_FC
+
+void serial_irq_handler(serial_t *obj, uart_irq_handler handler, uint32_t id)
+{
+    // Flush Tx FIFO. Otherwise, output data may get lost on this change.
+    while (! UART_IS_TX_EMPTY((UART_T *) NU_MODBASE(obj->serial.uart)));
+
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    obj->serial.irq_handler = (uint32_t) handler;
+    obj->serial.irq_id = id;
+
+    // Restore sync-mode vector
+    obj->serial.vec = ((struct nu_uart_var *) modinit->var)->vec;
+}
+
+void serial_irq_set(serial_t *obj, SerialIrq irq, uint32_t enable)
+{
+    obj->serial.irq_en = enable;
+    serial_enable_interrupt(obj, irq, enable);
+}
+
+int serial_getc(serial_t *obj)
+{
+    // NOTE: Every byte access requires accompaniment of one interrupt. This has side effect of performance degradation.
+    while (! serial_readable(obj));
+    int c = UART_READ(((UART_T *) NU_MODBASE(obj->serial.uart)));
+
+    // NOTE: On Nuvoton targets, no H/W IRQ to match TxIrq/RxIrq.
+    //       Simulation of TxIrq/RxIrq requires the call to Serial::putc()/Serial::getc() respectively.
+    if (obj->serial.inten_msk & (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk)) {
+        UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+    }
+
+    return c;
+}
+
+void serial_putc(serial_t *obj, int c)
+{
+    // NOTE: Every byte access requires accompaniment of one interrupt. This has side effect of performance degradation.
+    while (! serial_writable(obj));
+    UART_WRITE(((UART_T *) NU_MODBASE(obj->serial.uart)), c);
+
+    // NOTE: On Nuvoton targets, no H/W IRQ to match TxIrq/RxIrq.
+    //       Simulation of TxIrq/RxIrq requires the call to Serial::putc()/Serial::getc() respectively.
+    if (obj->serial.inten_msk & UART_INTEN_THREIEN_Msk) {
+        UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_THREIEN_Msk);
+    }
+}
+
+int serial_readable(serial_t *obj)
+{
+    return ! UART_GET_RX_EMPTY(((UART_T *) NU_MODBASE(obj->serial.uart)));
+}
+
+int serial_writable(serial_t *obj)
+{
+    return ! UART_IS_TX_FULL(((UART_T *) NU_MODBASE(obj->serial.uart)));
+}
+
+void serial_pinout_tx(PinName tx)
+{
+    pinmap_pinout(tx, PinMap_UART_TX);
+}
+
+void serial_break_set(serial_t *obj)
+{
+    ((UART_T *) NU_MODBASE(obj->serial.uart))->LINE |= UART_LINE_BCB_Msk;
+}
+
+void serial_break_clear(serial_t *obj)
+{
+    ((UART_T *) NU_MODBASE(obj->serial.uart))->LINE &= ~UART_LINE_BCB_Msk;
+}
+
+static void uart0_vec(void)
+{
+    uart_irq(uart0_var.obj);
+}
+
+static void uart1_vec(void)
+{
+    uart_irq(uart1_var.obj);
+}
+
+static void uart2_vec(void)
+{
+    uart_irq(uart2_var.obj);
+}
+
+static void uart3_vec(void)
+{
+    uart_irq(uart3_var.obj);
+}
+
+static void uart4_vec(void)
+{
+    uart_irq(uart4_var.obj);
+}
+
+static void uart5_vec(void)
+{
+    uart_irq(uart5_var.obj);
+}
+
+static void uart_irq(serial_t *obj)
+{
+    UART_T *uart_base = (UART_T *) NU_MODBASE(obj->serial.uart);
+
+    if (uart_base->INTSTS & (UART_INTSTS_RDAINT_Msk | UART_INTSTS_RXTOINT_Msk)) {
+        // Simulate clear of the interrupt flag. Temporarily disable the interrupt here and to be recovered on next read.
+        UART_DISABLE_INT(uart_base, (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+        if (obj->serial.irq_handler) {
+            ((uart_irq_handler) obj->serial.irq_handler)(obj->serial.irq_id, RxIrq);
+        }
+    }
+
+    if (uart_base->INTSTS & UART_INTSTS_THREINT_Msk) {
+        // Simulate clear of the interrupt flag. Temporarily disable the interrupt here and to be recovered on next write.
+        UART_DISABLE_INT(uart_base, UART_INTEN_THREIEN_Msk);
+        if (obj->serial.irq_handler) {
+            ((uart_irq_handler) obj->serial.irq_handler)(obj->serial.irq_id, TxIrq);
+        }
+    }
+
+    // FIXME: Ignore all other interrupt flags. Clear them. Otherwise, program will get stuck in interrupt.
+    uart_base->INTSTS = uart_base->INTSTS;
+    uart_base->FIFOSTS = uart_base->FIFOSTS;
+}
+
+
+#if DEVICE_SERIAL_ASYNCH
+int serial_tx_asynch(serial_t *obj, const void *tx, size_t tx_length, uint8_t tx_width, uint32_t handler, uint32_t event, DMAUsage hint)
+{
+    MBED_ASSERT(tx_width == 8 || tx_width == 16 || tx_width == 32);
+
+    obj->serial.dma_usage_tx = hint;
+    serial_check_dma_usage(&obj->serial.dma_usage_tx, &obj->serial.dma_chn_id_tx);
+
+    // UART IRQ is necessary for both interrupt way and DMA way
+    serial_tx_enable_event(obj, event, 1);
+    serial_tx_buffer_set(obj, tx, tx_length, tx_width);
+
+    int n_word = 0;
+    if (obj->serial.dma_usage_tx == DMA_USAGE_NEVER) {
+        // Interrupt way
+        n_word = serial_write_async(obj);
+        serial_tx_enable_interrupt(obj, handler, 1);
+    } else {
+        // DMA way
+        const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+        MBED_ASSERT(modinit != NULL);
+        MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+        PDMA_T *pdma_base = dma_modbase();
+
+        pdma_base->CHCTL |= 1 << obj->serial.dma_chn_id_tx;     // Enable this DMA channel
+        PDMA_SetTransferMode(pdma_base,
+                             obj->serial.dma_chn_id_tx,
+                             ((struct nu_uart_var *) modinit->var)->pdma_perp_tx,   // Peripheral connected to this PDMA
+                             0,                 // Scatter-gather disabled
+                             0);                // Scatter-gather descriptor address
+        PDMA_SetTransferCnt(pdma_base,
+                            obj->serial.dma_chn_id_tx,
+                            (tx_width == 8) ? PDMA_WIDTH_8 : (tx_width == 16) ? PDMA_WIDTH_16 : PDMA_WIDTH_32,
+                            tx_length);
+        PDMA_SetTransferAddr(pdma_base,
+                             obj->serial.dma_chn_id_tx,
+                             (uint32_t) tx,     // NOTE:
+                                                // NUC472: End of source address
+                                                // M451: Start of source address
+                                                // M480: Start of source address
+                                                // M2351: Start of source address
+                             PDMA_SAR_INC,      // Source address incremental
+                             (uint32_t) NU_MODBASE(obj->serial.uart),   // Destination address
+                             PDMA_DAR_FIX);     // Destination address fixed
+        PDMA_SetBurstType(pdma_base,
+                          obj->serial.dma_chn_id_tx,
+                          PDMA_REQ_SINGLE,      // Single mode
+                          0); // Burst size
+        PDMA_EnableInt(pdma_base,
+                       obj->serial.dma_chn_id_tx,
+                       PDMA_INT_TRANS_DONE);    // Interrupt type
+        // Register DMA event handler
+        dma_set_handler(obj->serial.dma_chn_id_tx, (uint32_t) uart_dma_handler_tx, (uint32_t) obj, DMA_EVENT_ALL);
+        serial_tx_enable_interrupt(obj, handler, 1);
+        /* We needn't actually enable UART INT to go UART ISR -> handler.
+         * Instead, as PDMA INT is triggered, we will go PDMA ISR -> UART ISR -> handler
+         * with serial_tx/rx_enable_interrupt having set up this call path. */
+        UART_DISABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_THREIEN_Msk);
+
+        ((UART_T *) NU_MODBASE(obj->serial.uart))->INTEN |= UART_INTEN_TXPDMAEN_Msk;  // Start DMA transfer
+    }
+
+    return n_word;
+}
+
+void serial_rx_asynch(serial_t *obj, void *rx, size_t rx_length, uint8_t rx_width, uint32_t handler, uint32_t event, uint8_t char_match, DMAUsage hint)
+{
+    MBED_ASSERT(rx_width == 8 || rx_width == 16 || rx_width == 32);
+
+    obj->serial.dma_usage_rx = hint;
+    serial_check_dma_usage(&obj->serial.dma_usage_rx, &obj->serial.dma_chn_id_rx);
+    // DMA doesn't support char match, so fall back to IRQ if it is requested.
+    if (obj->serial.dma_usage_rx != DMA_USAGE_NEVER &&
+            (event & SERIAL_EVENT_RX_CHARACTER_MATCH) &&
+            char_match != SERIAL_RESERVED_CHAR_MATCH) {
+        obj->serial.dma_usage_rx = DMA_USAGE_NEVER;
+        dma_channel_free(obj->serial.dma_chn_id_rx);
+        obj->serial.dma_chn_id_rx = DMA_ERROR_OUT_OF_CHANNELS;
+    }
+
+    // UART IRQ is necessary for both interrupt way and DMA way
+    serial_rx_enable_event(obj, event, 1);
+    serial_rx_buffer_set(obj, rx, rx_length, rx_width);
+    serial_rx_set_char_match(obj, char_match);
+
+    if (obj->serial.dma_usage_rx == DMA_USAGE_NEVER) {
+        // Interrupt way
+        serial_rx_enable_interrupt(obj, handler, 1);
+    } else {
+        // DMA way
+        const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+        MBED_ASSERT(modinit != NULL);
+        MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+        PDMA_T *pdma_base = dma_modbase();
+
+        pdma_base->CHCTL |= 1 << obj->serial.dma_chn_id_rx;     // Enable this DMA channel
+        PDMA_SetTransferMode(pdma_base,
+                             obj->serial.dma_chn_id_rx,
+                             ((struct nu_uart_var *) modinit->var)->pdma_perp_rx,   // Peripheral connected to this PDMA
+                             0,  // Scatter-gather disabled
+                             0); // Scatter-gather descriptor address
+        PDMA_SetTransferCnt(pdma_base,
+                            obj->serial.dma_chn_id_rx,
+                            (rx_width == 8) ? PDMA_WIDTH_8 : (rx_width == 16) ? PDMA_WIDTH_16 : PDMA_WIDTH_32,
+                            rx_length);
+        PDMA_SetTransferAddr(pdma_base,
+                             obj->serial.dma_chn_id_rx,
+                             (uint32_t) NU_MODBASE(obj->serial.uart),    // Source address
+                             PDMA_SAR_FIX,      // Source address fixed
+                             (uint32_t) rx,     // NOTE:
+                                                // NUC472: End of destination address
+                                                // M451: Start of destination address
+                                                // M480: Start of destination address
+                                                // M2351: Start of destination address
+                             PDMA_DAR_INC);     // Destination address incremental
+        PDMA_SetBurstType(pdma_base,
+                          obj->serial.dma_chn_id_rx,
+                          PDMA_REQ_SINGLE,      // Single mode
+                          0);                   // Burst size
+        PDMA_EnableInt(pdma_base,
+                       obj->serial.dma_chn_id_rx,
+                       PDMA_INT_TRANS_DONE);    // Interrupt type
+        // Register DMA event handler
+        dma_set_handler(obj->serial.dma_chn_id_rx, (uint32_t) uart_dma_handler_rx, (uint32_t) obj, DMA_EVENT_ALL);
+        serial_rx_enable_interrupt(obj, handler, 1);
+        /* We needn't actually enable UART INT to go UART ISR -> handler.
+         * Instead, as PDMA INT is triggered, we will go PDMA ISR -> UART ISR -> handler
+         * with serial_tx/rx_enable_interrupt having set up this call path. */
+        UART_DISABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+        ((UART_T *) NU_MODBASE(obj->serial.uart))->INTEN |= UART_INTEN_RXPDMAEN_Msk;    // Start DMA transfer
+    }
+}
+
+void serial_tx_abort_asynch(serial_t *obj)
+{
+    // Flush Tx FIFO. Otherwise, output data may get lost on this change.
+    while (! UART_IS_TX_EMPTY((UART_T *) NU_MODBASE(obj->serial.uart)));
+
+    if (obj->serial.dma_usage_tx != DMA_USAGE_NEVER) {
+        PDMA_T *pdma_base = dma_modbase();
+
+        if (obj->serial.dma_chn_id_tx != DMA_ERROR_OUT_OF_CHANNELS) {
+            PDMA_DisableInt(pdma_base, obj->serial.dma_chn_id_tx, PDMA_INT_TRANS_DONE);
+            // NOTE: On NUC472, next PDMA transfer will fail with PDMA_STOP() called. Cause is unknown.
+            pdma_base->CHCTL &= ~(1 << obj->serial.dma_chn_id_tx);
+        }
+        UART_DISABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_TXPDMAEN_Msk);
+    }
+
+    // Necessary for both interrupt way and DMA way
+    serial_enable_interrupt(obj, TxIrq, 0);
+    serial_rollback_interrupt(obj, TxIrq);
+}
+
+void serial_rx_abort_asynch(serial_t *obj)
+{
+    if (obj->serial.dma_usage_rx != DMA_USAGE_NEVER) {
+        PDMA_T *pdma_base = dma_modbase();
+
+        if (obj->serial.dma_chn_id_rx != DMA_ERROR_OUT_OF_CHANNELS) {
+            PDMA_DisableInt(pdma_base, obj->serial.dma_chn_id_rx, PDMA_INT_TRANS_DONE);
+            // NOTE: On NUC472, next PDMA transfer will fail with PDMA_STOP() called. Cause is unknown.
+            pdma_base->CHCTL &= ~(1 << obj->serial.dma_chn_id_rx);
+        }
+        UART_DISABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_RXPDMAEN_Msk);
+    }
+
+    // Necessary for both interrupt way and DMA way
+    serial_enable_interrupt(obj, RxIrq, 0);
+    serial_rollback_interrupt(obj, RxIrq);
+}
+
+uint8_t serial_tx_active(serial_t *obj)
+{
+    // NOTE: Judge by serial_is_irq_en(obj, TxIrq) doesn't work with sync/async modes interleaved. Change with TX FIFO empty flag.
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+    return (obj->serial.vec == var->vec_async);
+}
+
+uint8_t serial_rx_active(serial_t *obj)
+{
+    // NOTE: Judge by serial_is_irq_en(obj, RxIrq) doesn't work with sync/async modes interleaved. Change with RX FIFO empty flag.
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+    return (obj->serial.vec == var->vec_async);
+}
+
+int serial_irq_handler_asynch(serial_t *obj)
+{
+    int event_rx = 0;
+    int event_tx = 0;
+
+    // Necessary for both interrupt way and DMA way
+    if (serial_is_irq_en(obj, RxIrq)) {
+        event_rx = serial_rx_event_check(obj);
+        if (event_rx) {
+            serial_rx_abort_asynch(obj);
+        }
+    }
+
+    if (serial_is_irq_en(obj, TxIrq)) {
+        event_tx = serial_tx_event_check(obj);
+        if (event_tx) {
+            serial_tx_abort_asynch(obj);
+        }
+    }
+
+    return (obj->serial.event & (event_rx | event_tx));
+}
+
+static void uart0_vec_async(void)
+{
+    uart_irq_async(uart0_var.obj);
+}
+
+static void uart1_vec_async(void)
+{
+    uart_irq_async(uart1_var.obj);
+}
+
+static void uart2_vec_async(void)
+{
+    uart_irq_async(uart2_var.obj);
+}
+
+static void uart3_vec_async(void)
+{
+    uart_irq_async(uart3_var.obj);
+}
+
+static void uart4_vec_async(void)
+{
+    uart_irq_async(uart4_var.obj);
+}
+
+static void uart5_vec_async(void)
+{
+    uart_irq_async(uart5_var.obj);
+}
+
+static void uart_irq_async(serial_t *obj)
+{
+    if (serial_is_irq_en(obj, RxIrq)) {
+        (*obj->serial.irq_handler_rx_async)();
+    }
+    if (serial_is_irq_en(obj, TxIrq)) {
+        (*obj->serial.irq_handler_tx_async)();
+    }
+}
+
+static void serial_rx_set_char_match(serial_t *obj, uint8_t char_match)
+{
+    obj->char_match = char_match;
+    obj->char_found = 0;
+}
+
+static void serial_tx_enable_event(serial_t *obj, int event, uint8_t enable)
+{
+    obj->serial.event &= ~SERIAL_EVENT_TX_MASK;
+    obj->serial.event |= (event & SERIAL_EVENT_TX_MASK);
+
+    if (event & SERIAL_EVENT_TX_COMPLETE) {
+        // N/A
+    }
+}
+
+static void serial_rx_enable_event(serial_t *obj, int event, uint8_t enable)
+{
+    obj->serial.event &= ~SERIAL_EVENT_RX_MASK;
+    obj->serial.event |= (event & SERIAL_EVENT_RX_MASK);
+
+    if (event & SERIAL_EVENT_RX_COMPLETE) {
+        // N/A
+    }
+    if (event & SERIAL_EVENT_RX_OVERRUN_ERROR) {
+        // N/A
+    }
+    if (event & SERIAL_EVENT_RX_FRAMING_ERROR) {
+        UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_RLSIEN_Msk);
+    }
+    if (event & SERIAL_EVENT_RX_PARITY_ERROR) {
+        UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_RLSIEN_Msk);
+    }
+    if (event & SERIAL_EVENT_RX_OVERFLOW) {
+        UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_BUFERRIEN_Msk);
+    }
+    if (event & SERIAL_EVENT_RX_CHARACTER_MATCH) {
+        // N/A
+    }
+}
+
+static int serial_is_tx_complete(serial_t *obj)
+{
+    // NOTE: Exclude tx fifo empty check due to no such interrupt on DMA way
+    return (obj->tx_buff.pos == obj->tx_buff.length);
+}
+
+static int serial_is_rx_complete(serial_t *obj)
+{
+    return (obj->rx_buff.pos == obj->rx_buff.length);
+}
+
+static uint32_t serial_tx_event_check(serial_t *obj)
+{
+    UART_T *uart_base = (UART_T *) NU_MODBASE(obj->serial.uart);
+
+    if (uart_base->INTSTS & UART_INTSTS_THREINT_Msk) {
+        // Simulate clear of the interrupt flag. Temporarily disable the interrupt here and to be recovered on next write.
+        UART_DISABLE_INT(uart_base, UART_INTEN_THREIEN_Msk);
+    }
+
+    uint32_t event = 0;
+
+    if (obj->serial.dma_usage_tx == DMA_USAGE_NEVER) {
+        serial_write_async(obj);
+    }
+
+    if (serial_is_tx_complete(obj)) {
+        event |= SERIAL_EVENT_TX_COMPLETE;
+    }
+
+    return event;
+}
+
+static uint32_t serial_rx_event_check(serial_t *obj)
+{
+    UART_T *uart_base = (UART_T *) NU_MODBASE(obj->serial.uart);
+
+    if (uart_base->INTSTS & (UART_INTSTS_RDAINT_Msk | UART_INTSTS_RXTOINT_Msk)) {
+        // Simulate clear of the interrupt flag. Temporarily disable the interrupt here and to be recovered on next read.
+        UART_DISABLE_INT(uart_base, (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+    }
+
+    uint32_t event = 0;
+
+    if (uart_base->FIFOSTS & UART_FIFOSTS_BIF_Msk) {
+        uart_base->FIFOSTS = UART_FIFOSTS_BIF_Msk;
+    }
+    if (uart_base->FIFOSTS & UART_FIFOSTS_FEF_Msk) {
+        uart_base->FIFOSTS = UART_FIFOSTS_FEF_Msk;
+        event |= SERIAL_EVENT_RX_FRAMING_ERROR;
+    }
+    if (uart_base->FIFOSTS & UART_FIFOSTS_PEF_Msk) {
+        uart_base->FIFOSTS = UART_FIFOSTS_PEF_Msk;
+        event |= SERIAL_EVENT_RX_PARITY_ERROR;
+    }
+
+    if (uart_base->FIFOSTS & UART_FIFOSTS_RXOVIF_Msk) {
+        uart_base->FIFOSTS = UART_FIFOSTS_RXOVIF_Msk;
+        event |= SERIAL_EVENT_RX_OVERFLOW;
+    }
+
+    if (obj->serial.dma_usage_rx == DMA_USAGE_NEVER) {
+        serial_read_async(obj);
+    }
+
+    if (serial_is_rx_complete(obj)) {
+        event |= SERIAL_EVENT_RX_COMPLETE;
+    }
+    if ((obj->char_match != SERIAL_RESERVED_CHAR_MATCH) && obj->char_found) {
+        event |= SERIAL_EVENT_RX_CHARACTER_MATCH;
+    }
+
+    return event;
+}
+
+static void uart_dma_handler_tx(uint32_t id, uint32_t event_dma)
+{
+    serial_t *obj = (serial_t *) id;
+
+    // FIXME: Pass this error to caller
+    if (event_dma & DMA_EVENT_ABORT) {
+    }
+    // Expect UART IRQ will catch this transfer done event
+    if (event_dma & DMA_EVENT_TRANSFER_DONE) {
+        obj->tx_buff.pos = obj->tx_buff.length;
+    }
+    // FIXME: Pass this error to caller
+    if (event_dma & DMA_EVENT_TIMEOUT) {
+    }
+
+    uart_irq_async(obj);
+}
+
+static void uart_dma_handler_rx(uint32_t id, uint32_t event_dma)
+{
+    serial_t *obj = (serial_t *) id;
+
+    // FIXME: Pass this error to caller
+    if (event_dma & DMA_EVENT_ABORT) {
+    }
+    // Expect UART IRQ will catch this transfer done event
+    if (event_dma & DMA_EVENT_TRANSFER_DONE) {
+        obj->rx_buff.pos = obj->rx_buff.length;
+    }
+    // FIXME: Pass this error to caller
+    if (event_dma & DMA_EVENT_TIMEOUT) {
+    }
+
+    uart_irq_async(obj);
+}
+
+static int serial_write_async(serial_t *obj)
+{
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    UART_T *uart_base = (UART_T *) NU_MODBASE(obj->serial.uart);
+
+    uint32_t tx_fifo_max = ((struct nu_uart_var *) modinit->var)->fifo_size_tx;
+    uint32_t tx_fifo_busy = (uart_base->FIFOSTS & UART_FIFOSTS_TXPTR_Msk) >> UART_FIFOSTS_TXPTR_Pos;
+    if (uart_base->FIFOSTS & UART_FIFOSTS_TXFULL_Msk) {
+        tx_fifo_busy = tx_fifo_max;
+    }
+    uint32_t tx_fifo_free = tx_fifo_max - tx_fifo_busy;
+    if (tx_fifo_free == 0) {
+        // Simulate clear of the interrupt flag
+        if (obj->serial.inten_msk & UART_INTEN_THREIEN_Msk) {
+            UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_THREIEN_Msk);
+        }
+        return 0;
+    }
+
+    uint32_t bytes_per_word = obj->tx_buff.width / 8;
+
+    uint8_t *tx = (uint8_t *)(obj->tx_buff.buffer) + bytes_per_word * obj->tx_buff.pos;
+    int n_words = 0;
+    while (obj->tx_buff.pos < obj->tx_buff.length && tx_fifo_free >= bytes_per_word) {
+        switch (bytes_per_word) {
+        case 4:
+            UART_WRITE(((UART_T *) NU_MODBASE(obj->serial.uart)), *tx ++);
+            UART_WRITE(((UART_T *) NU_MODBASE(obj->serial.uart)), *tx ++);
+        case 2:
+            UART_WRITE(((UART_T *) NU_MODBASE(obj->serial.uart)), *tx ++);
+        case 1:
+            UART_WRITE(((UART_T *) NU_MODBASE(obj->serial.uart)), *tx ++);
+        }
+
+        n_words ++;
+        tx_fifo_free -= bytes_per_word;
+        obj->tx_buff.pos ++;
+    }
+
+    if (n_words) {
+        // Simulate clear of the interrupt flag
+        if (obj->serial.inten_msk & UART_INTEN_THREIEN_Msk) {
+            UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_THREIEN_Msk);
+        }
+    }
+
+    return n_words;
+}
+
+static int serial_read_async(serial_t *obj)
+{
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    uint32_t rx_fifo_busy = (((UART_T *) NU_MODBASE(obj->serial.uart))->FIFOSTS & UART_FIFOSTS_RXPTR_Msk) >> UART_FIFOSTS_RXPTR_Pos;
+
+    uint32_t bytes_per_word = obj->rx_buff.width / 8;
+
+    uint8_t *rx = (uint8_t *)(obj->rx_buff.buffer) + bytes_per_word * obj->rx_buff.pos;
+    int n_words = 0;
+    while (obj->rx_buff.pos < obj->rx_buff.length && rx_fifo_busy >= bytes_per_word) {
+        switch (bytes_per_word) {
+        case 4:
+            *rx ++ = UART_READ(((UART_T *) NU_MODBASE(obj->serial.uart)));
+            *rx ++ = UART_READ(((UART_T *) NU_MODBASE(obj->serial.uart)));
+        case 2:
+            *rx ++ = UART_READ(((UART_T *) NU_MODBASE(obj->serial.uart)));
+        case 1:
+            *rx ++ = UART_READ(((UART_T *) NU_MODBASE(obj->serial.uart)));
+        }
+
+        n_words ++;
+        rx_fifo_busy -= bytes_per_word;
+        obj->rx_buff.pos ++;
+
+        if ((obj->serial.event & SERIAL_EVENT_RX_CHARACTER_MATCH) &&
+                obj->char_match != SERIAL_RESERVED_CHAR_MATCH) {
+            uint8_t *rx_cmp = rx;
+            switch (bytes_per_word) {
+            case 4:
+                rx_cmp -= 2;
+            case 2:
+                rx_cmp --;
+            case 1:
+                rx_cmp --;
+            }
+            if (*rx_cmp == obj->char_match) {
+                obj->char_found = 1;
+                break;
+            }
+        }
+    }
+
+    if (n_words) {
+        // Simulate clear of the interrupt flag
+        if (obj->serial.inten_msk & (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk)) {
+            UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+        }
+    }
+
+    return n_words;
+}
+
+static void serial_tx_buffer_set(serial_t *obj, const void *tx, size_t length, uint8_t width)
+{
+    obj->tx_buff.buffer = (void *) tx;
+    obj->tx_buff.length = length;
+    obj->tx_buff.pos = 0;
+    obj->tx_buff.width = width;
+}
+
+static void serial_rx_buffer_set(serial_t *obj, void *rx, size_t length, uint8_t width)
+{
+    obj->rx_buff.buffer = rx;
+    obj->rx_buff.length = length;
+    obj->rx_buff.pos = 0;
+    obj->rx_buff.width = width;
+}
+
+static void serial_tx_enable_interrupt(serial_t *obj, uint32_t handler, uint8_t enable)
+{
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    // Necessary for both interrupt way and DMA way
+    struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+    // With our own async vector, tx/rx handlers can be different.
+    obj->serial.vec = var->vec_async;
+    obj->serial.irq_handler_tx_async = (void (*)(void)) handler;
+    serial_enable_interrupt(obj, TxIrq, enable);
+}
+
+static void serial_rx_enable_interrupt(serial_t *obj, uint32_t handler, uint8_t enable)
+{
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    // Necessary for both interrupt way and DMA way
+    struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+    // With our own async vector, tx/rx handlers can be different.
+    obj->serial.vec = var->vec_async;
+    obj->serial.irq_handler_rx_async = (void (*) (void)) handler;
+    serial_enable_interrupt(obj, RxIrq, enable);
+}
+
+static void serial_enable_interrupt(serial_t *obj, SerialIrq irq, uint32_t enable)
+{
+    if (enable) {
+        const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+        MBED_ASSERT(modinit != NULL);
+        MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+        NVIC_SetVector(modinit->irq_n, (uint32_t) obj->serial.vec);
+        NVIC_EnableIRQ(modinit->irq_n);
+
+        struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+        // Multiple serial S/W objects for single UART H/W module possibly.
+        // Bind serial S/W object to UART H/W module as interrupt is enabled.
+        var->obj = obj;
+
+        switch (irq) {
+        // NOTE: Setting inten_msk first to avoid race condition
+        case RxIrq:
+            obj->serial.inten_msk = obj->serial.inten_msk | (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk);
+            UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+            break;
+        case TxIrq:
+            obj->serial.inten_msk = obj->serial.inten_msk | UART_INTEN_THREIEN_Msk;
+            UART_ENABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_THREIEN_Msk);
+            break;
+        }
+    } else { // disable
+        switch (irq) {
+        case RxIrq:
+            UART_DISABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk));
+            obj->serial.inten_msk = obj->serial.inten_msk & ~(UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk);
+            break;
+        case TxIrq:
+            UART_DISABLE_INT(((UART_T *) NU_MODBASE(obj->serial.uart)), UART_INTEN_THREIEN_Msk);
+            obj->serial.inten_msk = obj->serial.inten_msk & ~UART_INTEN_THREIEN_Msk;
+            break;
+        }
+    }
+}
+
+static void serial_rollback_interrupt(serial_t *obj, SerialIrq irq)
+{
+    const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+    MBED_ASSERT(modinit != NULL);
+    MBED_ASSERT(modinit->modname == (int) obj->serial.uart);
+
+    struct nu_uart_var *var = (struct nu_uart_var *) modinit->var;
+
+    obj->serial.vec = var->vec;
+    serial_enable_interrupt(obj, irq, obj->serial.irq_en);
+}
+
+static void serial_check_dma_usage(DMAUsage *dma_usage, int *dma_ch)
+{
+    if (*dma_usage != DMA_USAGE_NEVER) {
+        if (*dma_ch == DMA_ERROR_OUT_OF_CHANNELS) {
+            *dma_ch = dma_channel_allocate(DMA_CAP_NONE);
+        }
+        if (*dma_ch == DMA_ERROR_OUT_OF_CHANNELS) {
+            *dma_usage = DMA_USAGE_NEVER;
+        }
+    } else {
+        dma_channel_free(*dma_ch);
+        *dma_ch = DMA_ERROR_OUT_OF_CHANNELS;
+    }
+}
+
+static int serial_is_irq_en(serial_t *obj, SerialIrq irq)
+{
+    int inten_msk = 0;
+
+    switch (irq) {
+    case RxIrq:
+        inten_msk = obj->serial.inten_msk & (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk);
+        break;
+    case TxIrq:
+        inten_msk = obj->serial.inten_msk & UART_INTEN_THREIEN_Msk;
+        break;
+    }
+
+    return !! inten_msk;
+}
+
+#endif  // #if DEVICE_SERIAL_ASYNCH
+#endif  // #if DEVICE_SERIAL