mbed library sources. With a patch for the can_api

Fork of mbed-dev by mbed official

Revision:
149:156823d33999
Parent:
144:ef7eb2e8f9f7
diff -r 21d94c44109e -r 156823d33999 targets/TARGET_NUVOTON/TARGET_NUC472/serial_api.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/serial_api.c	Fri Oct 28 11:17:30 2016 +0100
@@ -0,0 +1,1097 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2015-2016 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"
+
+#if DEVICE_SERIAL_ASYNCH
+#include "dma_api.h"
+#include "dma.h"
+#endif
+
+struct nu_uart_var {
+    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 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 = {
+    .obj                =   NULL,
+    .fifo_size_tx       =   64,
+    .fifo_size_rx       =   64,
+    .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 = {
+    .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 = {
+    .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 = {
+    .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 = {
+    .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 = {
+    .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_UARTSEL_HIRC, CLK_CLKDIV0_UART(1), UART0_RST, UART0_IRQn, &uart0_var},
+    {UART_1, UART1_MODULE, CLK_CLKSEL1_UARTSEL_HIRC, CLK_CLKDIV0_UART(1), UART1_RST, UART1_IRQn, &uart1_var},
+    {UART_2, UART2_MODULE, CLK_CLKSEL1_UARTSEL_HIRC, CLK_CLKDIV0_UART(1), UART2_RST, UART2_IRQn, &uart2_var},
+    {UART_3, UART3_MODULE, CLK_CLKSEL1_UARTSEL_HIRC, CLK_CLKDIV0_UART(1), UART3_RST, UART3_IRQn, &uart3_var},
+    {UART_4, UART4_MODULE, CLK_CLKSEL1_UARTSEL_HIRC, CLK_CLKDIV0_UART(1), UART4_RST, UART4_IRQn, &uart4_var},
+    {UART_5, UART5_MODULE, CLK_CLKSEL1_UARTSEL_HIRC, CLK_CLKDIV0_UART(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: 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 == obj->serial.uart);
+    
+    // Reset this module
+    SYS_ResetModule(modinit->rsetidx);
+    
+    // Select IP clock source
+    CLK_SetModuleClock(modinit->clkidx, modinit->clksrc, modinit->clkdiv);
+    // Enable IP clock
+    CLK_EnableModuleClock(modinit->clkidx);
+
+    pinmap_pinout(tx, PinMap_UART_TX);
+    pinmap_pinout(rx, PinMap_UART_RX);
+    // FIXME: Why PullUp?
+    //if (tx != NC) {
+    //    pin_mode(tx, PullUp);
+    //}
+    //if (rx != NC) {
+    //    pin_mode(rx, PullUp);
+    //}
+    obj->serial.pin_tx = tx;
+    obj->serial.pin_rx = rx;
+    
+    // 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 = ((struct nu_uart_var *) modinit->var)->vec;
+    
+#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 == &stdio_uart) {
+        stdio_uart_inited = 1;
+        /* NOTE: Not required anymore because stdio_uart will be manually initialized in mbed-drivers/source/retarget.cpp from mbed beta */
+        //memcpy(&stdio_uart, obj, sizeof(serial_t));
+    }
+    
+    // Mark this module to be inited.
+    int i = modinit - uart_modinit_tab;
+    uart_modinit_mask |= 1 << i;
+}
+
+void serial_free(serial_t *obj)
+{
+#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
+
+    UART_Close((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 == 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
+    CLK_DisableModuleClock(modinit->clkidx);
+    
+    ((struct nu_uart_var *) modinit->var)->obj = NULL;
+    
+    if (obj == &stdio_uart) {
+        stdio_uart_inited = 0;
+    }
+    
+    // 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 *) 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 *) obj->serial.uart)));
+    
+    // TODO: Assert for not supported parity and data bits
+    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_SetLine_Config((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);
+        // nRTS pin output is high level active
+        uart_base->MODEM = (uart_base->MODEM & ~UART_MODEM_RTSACTLV_Msk) | UART_MODEM_RTSACTLV_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);
+        // nCTS pin input is high level active
+        uart_base->MODEMSTS = (uart_base->MODEMSTS & ~UART_MODEMSTS_CTSACTLV_Msk) | UART_MODEMSTS_CTSACTLV_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 *) 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 == obj->serial.uart);
+    
+    ((struct nu_uart_var *) modinit->var)->obj = obj;
+    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)
+{
+    if (enable) {
+        const struct nu_modinit_s *modinit = get_modinit(obj->serial.uart, uart_modinit_tab);
+        MBED_ASSERT(modinit != NULL);
+        MBED_ASSERT(modinit->modname == obj->serial.uart);
+    
+        NVIC_SetVector(modinit->irq_n, (uint32_t) obj->serial.vec);
+        NVIC_EnableIRQ(modinit->irq_n);
+        
+        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;
+        }
+    }
+}
+
+int serial_getc(serial_t *obj)
+{
+    // TODO: Fix every byte access requires accompaniness of one interrupt. This degrades performance much.    
+    while (! serial_readable(obj));
+    int c = UART_READ(((UART_T *) NU_MODBASE(obj->serial.uart)));
+    
+    // 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 c;
+}
+
+void serial_putc(serial_t *obj, int c)
+{
+    // TODO: Fix every byte access requires accompaniness of one interrupt. This degrades performance much.
+    while (! serial_writable(obj));
+    UART_WRITE(((UART_T *) NU_MODBASE(obj->serial.uart)), c);
+    
+    // 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);
+    }
+}
+
+int serial_readable(serial_t *obj)
+{
+    //return UART_IS_RX_READY(((UART_T *) NU_MODBASE(obj->serial.uart)));
+    return ! (((UART_T *) NU_MODBASE(obj->serial.uart))->FIFOSTS & UART_FIFOSTS_RXEMPTY_Msk);
+}
+
+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)
+{
+    // NOTE: tx_width is deprecated. Assume its value is databits ceiled to the nearest number among 8, 16, and 32.
+    tx_width = (obj->serial.databits <= 8) ? 8 : (obj->serial.databits <= 16) ? 16 : 32;
+    
+    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);
+    //UART_HAL_DisableTransmitter(obj->serial.address);
+    //UART_HAL_FlushTxFifo(obj->serial.address);
+    //UART_HAL_EnableTransmitter(obj->serial.address);
+            
+    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 == obj->serial.uart);
+    
+        PDMA->CHCTL |= 1 << obj->serial.dma_chn_id_tx;  // Enable this DMA channel
+        PDMA_SetTransferMode(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(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(obj->serial.dma_chn_id_tx, 
+            ((uint32_t) tx) + (tx_width / 8) * tx_length,   // NOTE: End of source address
+            PDMA_SAR_INC,   // Source address incremental
+            (uint32_t) obj->serial.uart,    // Destination address
+            PDMA_DAR_FIX);  // Destination address fixed
+        PDMA_SetBurstType(obj->serial.dma_chn_id_tx, 
+            PDMA_REQ_SINGLE,    // Single mode
+            0); // Burst size
+        PDMA_EnableInt(obj->serial.dma_chn_id_tx,
+            0); // Interrupt type. No use here
+        // 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);
+        ((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)
+{
+    // NOTE: rx_width is deprecated. Assume its value is databits ceiled to the nearest number among 8, 16, and 32.
+    rx_width = (obj->serial.databits <= 8) ? 8 : (obj->serial.databits <= 16) ? 16 : 32;
+    
+    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);
+    //UART_HAL_DisableReceiver(obj->serial.address);
+    //UART_HAL_FlushRxFifo(obj->serial.address);
+    //UART_HAL_EnableReceiver(obj->serial.address);
+        
+    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 == obj->serial.uart);
+    
+        PDMA->CHCTL |= 1 << obj->serial.dma_chn_id_rx;  // Enable this DMA channel
+        PDMA_SetTransferMode(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(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(obj->serial.dma_chn_id_rx,
+            (uint32_t) obj->serial.uart,    // Source address
+            PDMA_SAR_FIX,   // Source address fixed
+            ((uint32_t) rx) + (rx_width / 8) * rx_length,   // NOTE: End of destination address
+            PDMA_DAR_INC);  // Destination address incremental
+        PDMA_SetBurstType(obj->serial.dma_chn_id_rx, 
+            PDMA_REQ_SINGLE,    // Single mode
+            0); // Burst size
+        PDMA_EnableInt(obj->serial.dma_chn_id_rx,
+            0); // Interrupt type. No use here
+        // 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);
+        ((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 *) obj->serial.uart)));
+    
+    if (obj->serial.dma_usage_tx != DMA_USAGE_NEVER) {
+        if (obj->serial.dma_chn_id_tx != DMA_ERROR_OUT_OF_CHANNELS) {
+            PDMA_DisableInt(obj->serial.dma_chn_id_tx, 0);
+            // FIXME: Next PDMA transfer will fail with PDMA_STOP() called. Cause is unknown.
+            //PDMA_STOP(obj->serial.dma_chn_id_tx);
+            PDMA->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_irq_set(obj, TxIrq, 0);
+    // FIXME: more complete abort operation
+    //UART_HAL_DisableTransmitter(obj->serial.serial.address);
+    //UART_HAL_FlushTxFifo(obj->serial.serial.address);
+}
+
+void serial_rx_abort_asynch(serial_t *obj)
+{
+    if (obj->serial.dma_usage_rx != DMA_USAGE_NEVER) {
+        if (obj->serial.dma_chn_id_rx != DMA_ERROR_OUT_OF_CHANNELS) {
+            PDMA_DisableInt(obj->serial.dma_chn_id_rx, 0);
+            // FIXME: Next PDMA transfer will fail with PDMA_STOP() called. Cause is unknown.
+            //PDMA_STOP(obj->serial.dma_chn_id_rx);
+            PDMA->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_irq_set(obj, RxIrq, 0);
+    // FIXME: more complete abort operation
+    //UART_HAL_DisableReceiver(obj->serial.serial.address);
+    //UART_HAL_FlushRxFifo(obj->serial.serial.address);
+}
+
+uint8_t serial_tx_active(serial_t *obj)
+{
+    return serial_is_irq_en(obj, TxIrq);
+}
+
+uint8_t serial_rx_active(serial_t *obj)
+{
+    return serial_is_irq_en(obj, RxIrq);
+}
+
+int serial_irq_handler_asynch(serial_t *obj)
+{
+    int event_rx = 0;
+    int event_tx = 0;
+    
+    // Necessary for both interrup 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));
+}
+
+int serial_allow_powerdown(void)
+{
+    uint32_t modinit_mask = uart_modinit_mask;
+    while (modinit_mask) {
+        int uart_idx = nu_ctz(modinit_mask);
+        const struct nu_modinit_s *modinit = uart_modinit_tab + uart_idx;
+        if (modinit->modname != NC) {
+            UART_T *uart_base = (UART_T *) NU_MODBASE(modinit->modname);
+            // Disallow entering power-down mode if Tx FIFO has data to flush
+            if (! UART_IS_TX_EMPTY((uart_base))) {
+                return 0;
+            }
+            // Disallow entering power-down mode if async Rx transfer (not PDMA) is on-going
+            if (uart_base->INTEN & (UART_INTEN_RDAIEN_Msk | UART_INTEN_RXTOIEN_Msk)) {
+                return 0;
+            }
+            // Disallow entering power-down mode if async Rx transfer (PDMA) is on-going
+            if (uart_base->INTEN & UART_INTEN_RXPDMAEN_Msk) {
+                return 0;
+            }
+        }
+        modinit_mask &= ~(1 << uart_idx);
+    }
+    
+    return 1;
+}
+
+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) {
+    //}
+}
+
+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) {
+    //}
+    //if (event & SERIAL_EVENT_RX_OVERRUN_ERROR) {
+    //}
+    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) {
+    //}
+}
+
+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) && UART_GET_TX_EMPTY(((UART_T *) NU_MODBASE(obj->serial.uart)));
+    // FIXME: Premature abort???
+    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) && UART_GET_RX_EMPTY(((UART_T *) NU_MODBASE(obj->serial.uart)));
+    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;
+        // FIXME: Timing to reset char_found?
+        //obj->char_found = 0;
+    }
+    
+    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 == 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 == 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 rx_fifo_free = ((struct nu_uart_var *) modinit->var)->fifo_size_rx - rx_fifo_busy;
+    //if (rx_fifo_free == 0) {
+    //    return 0;
+    //}
+    
+    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 == obj->serial.uart);
+    
+    // Necessary for both interrupt way and DMA way
+    ((struct nu_uart_var *) modinit->var)->obj = obj;
+    // With our own async vector, tx/rx handlers can be different.
+    obj->serial.vec = ((struct nu_uart_var *) modinit->var)->vec_async;
+    obj->serial.irq_handler_tx_async = (void (*)(void)) handler;
+    serial_irq_set(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 == obj->serial.uart);
+    
+    // Necessary for both interrupt way and DMA way
+    ((struct nu_uart_var *) modinit->var)->obj = obj;
+    // With our own async vector, tx/rx handlers can be different.
+    obj->serial.vec = ((struct nu_uart_var *) modinit->var)->vec_async;
+    obj->serial.irq_handler_rx_async = (void (*) (void)) handler;
+    serial_irq_set(obj, RxIrq, enable);
+}
+
+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