nuttx/arch/xtensa/src/esp32/esp32_serial.c-代码预览-nuttx:基于 POSIX/ANSI 标准的实时操作系统项目

Oopenvela-robotdriver/serial: remove return value of up_putc()
/****************************************************************************
 * arch/xtensa/src/esp32/esp32_serial.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you 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.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <sys/types.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

#ifdef CONFIG_SERIAL_TERMIOS
#  include <termios.h>
#endif

#include <nuttx/irq.h>
#include <nuttx/arch.h>
#include <nuttx/fs/ioctl.h>
#include <nuttx/serial/serial.h>
#include <nuttx/spinlock.h>

#include <arch/board/board.h>

#include "xtensa.h"
#include "hardware/esp32_soc.h"
#include "hardware/esp32_iomux.h"
#include "hardware/esp32_gpio_sigmap.h"
#include "hardware/esp32_uart.h"
#include "hardware/esp32_uhci.h"
#include "hardware/esp32_dma.h"
#include "esp32_config.h"
#include "esp32_gpio.h"
#include "esp32_irq.h"
#include "esp32_dma.h"
#include "hardware/esp32_dport.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

#ifdef USE_SERIALDRIVER

/* Which UART with be tty0/console and which tty1-2? */

/* First pick the console and ttys0.  This could be any of UART0-5 */

#if defined(CONFIG_UART0_SERIAL_CONSOLE)
#  define CONSOLE_DEV           g_uart0port  /* UART0 is console */
#  define TTYS0_DEV             g_uart0port  /* UART0 is ttyS0 */
#  define UART0_ASSIGNED        1
#elif defined(CONFIG_UART1_SERIAL_CONSOLE)
#  define CONSOLE_DEV           g_uart1port  /* UART1 is console */
#  define TTYS0_DEV             g_uart1port  /* UART1 is ttyS0 */
#  define UART1_ASSIGNED        1
#elif defined(CONFIG_UART2_SERIAL_CONSOLE)
#  define CONSOLE_DEV           g_uart2port  /* UART2 is console */
#  define TTYS0_DEV             g_uart2port  /* UART2 is ttyS0 */
#  define UART2_ASSIGNED        1
#else
#  undef CONSOLE_DEV                         /* No console */
#  if defined(CONFIG_ESP32_UART0)
#    define TTYS0_DEV           g_uart0port  /* UART0 is ttyS0 */
#    define UART0_ASSIGNED      1
#  elif defined(CONFIG_ESP32_UART1)
#    define TTYS0_DEV           g_uart1port  /* UART1 is ttyS0 */
#    define UART1_ASSIGNED      1
#  elif defined(CONFIG_ESP32_UART2)
#    define TTYS0_DEV           g_uart2port  /* UART2 is ttyS0 */
#    define UART2_ASSIGNED      1
#  endif
#endif

/* Pick ttys1.  This could be any of UART0-2 excluding the console
 * UART.
 */

#if defined(CONFIG_ESP32_UART0) && !defined(UART0_ASSIGNED)
#  define TTYS1_DEV           g_uart0port  /* UART0 is ttyS1 */
#  define UART0_ASSIGNED      1
#elif defined(CONFIG_ESP32_UART1) && !defined(UART1_ASSIGNED)
#  define TTYS1_DEV           g_uart1port  /* UART1 is ttyS1 */
#  define UART1_ASSIGNED      1
#elif defined(CONFIG_ESP32_UART2) && !defined(UART2_ASSIGNED)
#  define TTYS1_DEV           g_uart2port  /* UART2 is ttyS1 */
#  define UART2_ASSIGNED      1
#endif

/* Pick ttys2.  This could be one of UART1-2. It can't be UART0
 * because that was either assigned as ttyS0 or ttys1.  One of these
 * could also be the console.
 */

#if defined(CONFIG_ESP32_UART1) && !defined(UART1_ASSIGNED)
#  define TTYS2_DEV           g_uart1port  /* UART1 is ttyS2 */
#  define UART1_ASSIGNED      1
#elif defined(CONFIG_ESP32_UART2) && !defined(UART2_ASSIGNED)
#  define TTYS2_DEV           g_uart2port  /* UART2 is ttyS2 */
#  define UART2_ASSIGNED      1
#endif

/* UART source clock for BAUD generation */

#define UART_CLK_FREQ         APB_CLK_FREQ

/* DMA related */

#ifdef CONFIG_SERIAL_RXDMA
#  error "SERIAL_RXDMA is not supported in ESP32 due to a hardware issue"
#endif

#ifdef CONFIG_SERIAL_TXDMA

#define UART_SELECT_SHIFT     UHCI_UART0_CE_S

/* UART DMA RX/TX number of descriptors */

#define UART_DMADESC_NUM     (CONFIG_UART_DMADESC_NUM)

/* In case the three UARTs select TX DMA support,
 * let DMA 0 exclusive to one and DMA 1
 * shared with others.
 */

#if defined(CONFIG_ESP32_UART0_TXDMA) && defined(CONFIG_ESP32_UART1_TXDMA) && defined(CONFIG_ESP32_UART2_TXDMA)
#  ifdef CONFIG_ESP32_UART0_EXC
#    define UART0_DMA 0
#    define UART1_DMA 1
#    define UART2_DMA 1
#  elif defined(CONFIG_ESP32_UART1_EXC)
#    define UART0_DMA 1
#    define UART1_DMA 0
#    define UART2_DMA 1
#  elif defined(CONFIG_ESP32_UART2_EXC)
#    define UART0_DMA 1
#    define UART1_DMA 1
#    define UART2_DMA 0
#  endif
#  define USE_DMA0  1
#  define USE_DMA1  1
#else
#  ifdef CONFIG_ESP32_UART0_TXDMA
#    define UART0_DMA 0
#    define USE_DMA0  1
#  endif
#  ifdef CONFIG_ESP32_UART1_TXDMA
#    ifndef USE_DMA0
#      define UART1_DMA 0
#      define USE_DMA0  1
#    else
#      define UART1_DMA 1
#      define USE_DMA1  1
#    endif
#  endif
#  ifdef CONFIG_ESP32_UART2_TXDMA
#    ifndef USE_DMA0
#      define UART2_DMA 0
#      define USE_DMA0  1
#    else
#      define UART2_DMA 1
#      define USE_DMA1  1
#    endif
#  endif
#endif

/* UART DMA controllers */

#if defined(USE_DMA0) && defined(USE_DMA1)
#  define UART_DMA_CONTROLLERS_NUM 2
#else
#  define UART_DMA_CONTROLLERS_NUM 1
#endif

/* Semaphores to control access to each DMA.
 * Theses semaphores ensure a new transfer is
 * triggered only after the previous one is completed,
 * and it also avoids competing issues with multiple UART
 * instances requesting to the same DMA.
 */

#ifdef USE_DMA0
static sem_t g_dma0_sem = SEM_INITIALIZER(1);
#endif
#ifdef USE_DMA1
static sem_t g_dma1_sem = SEM_INITIALIZER(1);
#endif

/* UART DMA RX/TX descriptors */

struct esp32_dmadesc_s s_dma_rxdesc[UART_DMA_CONTROLLERS_NUM]
                                   [UART_DMADESC_NUM];
struct esp32_dmadesc_s s_dma_txdesc[UART_DMA_CONTROLLERS_NUM]
                                   [UART_DMADESC_NUM];

#endif

/****************************************************************************
 * Private Types
 ****************************************************************************/

/* Constant properties of the UART.  Other configuration setting may be
 * changeable via Termios IOCTL calls.
 */

struct esp32_config_s
{
  const uint8_t id;             /* UART id */
  uint8_t  periph;              /* UART peripheral ID */
  uint8_t  irq;                 /* IRQ number assigned to the peripheral */
  uint8_t  txpin;               /* Tx pin number (0-39) */
  uint8_t  rxpin;               /* Rx pin number (0-39) */
  uint8_t  txsig;               /* Tx signal */
  uint8_t  rxsig;               /* Rx signal */
#ifdef CONFIG_SERIAL_IFLOWCONTROL
  uint8_t  rtspin;              /* RTS pin number (0-39) */
  uint8_t  rtssig;              /* RTS signal */
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
  uint8_t  ctspin;              /* CTS pin number (0-39) */
  uint8_t  ctssig;              /* CTS signal */
#endif
#ifdef CONFIG_SERIAL_TXDMA
  uint8_t  dma_chan;            /* DMA instance 0-1 */
  sem_t   *dma_sem;             /* DMA semaphore */
#endif
#ifdef HAVE_RS485
  uint8_t  rs485_dir_gpio;      /* UART RS-485 DIR GPIO pin cfg */
  bool     rs485_dir_polarity;  /* UART RS-485 DIR TXEN polarity */
#endif
};

/* Current state of the UART */

struct esp32_dev_s
{
  const struct esp32_config_s *config; /* Constant configuration */
  uint32_t baud;                       /* Configured baud */
  uint32_t status;                     /* Saved status bits */
  int      cpuint;                     /* CPU interrupt assigned to this UART */
  uint8_t  cpu;                        /* CPU ID */
  uint8_t  parity;                     /* 0=none, 1=odd, 2=even */
  uint8_t  bits;                       /* Number of bits (5-9) */
  bool     stopbits2;                  /* true: Configure with 2 stop bits instead of 1 */
#ifdef CONFIG_SERIAL_TXDMA
  bool txdma;                          /* TX DMA enabled for this UART */
#endif
#ifdef CONFIG_SERIAL_IFLOWCONTROL
  bool iflow;                          /* Input flow control (RTS) enabled */
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
  bool oflow;                          /* Output flow control (CTS) enabled */
#endif
  spinlock_t lock;
};

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

static int  esp32_setup(struct uart_dev_s *dev);
static void esp32_shutdown(struct uart_dev_s *dev);
static int  esp32_attach(struct uart_dev_s *dev);
static void esp32_detach(struct uart_dev_s *dev);
static int  esp32_interrupt(int cpuint, void *context, void *arg);
static int  esp32_ioctl(struct file *filep, int cmd, unsigned long arg);
static int  esp32_receive(struct uart_dev_s *dev, unsigned int *status);
static void esp32_rxint(struct uart_dev_s *dev, bool enable);
static bool esp32_rxavailable(struct uart_dev_s *dev);
static void esp32_send(struct uart_dev_s *dev, int ch);
static void esp32_txint(struct uart_dev_s *dev, bool enable);
static bool esp32_txready(struct uart_dev_s *dev);
static bool esp32_txempty(struct uart_dev_s *dev);
#ifdef CONFIG_SERIAL_IFLOWCONTROL
static bool esp32_rxflowcontrol(struct uart_dev_s *dev,
                                unsigned int nbuffered, bool upper);
#endif
#ifdef CONFIG_SERIAL_TXDMA
static void esp32_dmasend(struct uart_dev_s *dev);
static void esp32_dmatxavail(struct uart_dev_s *dev);
static void dma_config(uint8_t dma_chan);
static void dma_attach(uint8_t dma_chan);
static inline void dma_enable_int(uint8_t dma_chan);
static inline void dma_disable_int(uint8_t dma_chan);
static int esp32_interrupt_dma(int cpuint, void *context, void *arg);
#endif

/****************************************************************************
 * Private Data
 ****************************************************************************/

#define UART_TX_FIFO_SIZE        128
#define UART_RX_FIFO_FULL_THRHD  112
#define UART_RX_TOUT_THRHD_VALUE 0x02
#define UART_RX_FLOW_THRHD_VALUE 64   /* Almost half RX FIFO size */

static const struct uart_ops_s g_uart_ops =
{
  .setup          = esp32_setup,
  .shutdown       = esp32_shutdown,
  .attach         = esp32_attach,
  .detach         = esp32_detach,
  .ioctl          = esp32_ioctl,
  .receive        = esp32_receive,
  .rxint          = esp32_rxint,
  .rxavailable    = esp32_rxavailable,
  .send           = esp32_send,
  .txint          = esp32_txint,
  .txready        = esp32_txready,
  .txempty        = esp32_txempty,
#ifdef CONFIG_SERIAL_IFLOWCONTROL
  .rxflowcontrol  = esp32_rxflowcontrol,
#endif
#ifdef CONFIG_SERIAL_TXDMA
  .dmasend        = esp32_dmasend,
  .dmatxavail     = esp32_dmatxavail,
#endif
};

/* I/O buffers */

#ifdef CONFIG_ESP32_UART0
static char g_uart0rxbuffer[CONFIG_UART0_RXBUFSIZE];
static char g_uart0txbuffer[CONFIG_UART0_TXBUFSIZE];
#endif
#ifdef CONFIG_ESP32_UART1
static char g_uart1rxbuffer[CONFIG_UART1_RXBUFSIZE];
static char g_uart1txbuffer[CONFIG_UART1_TXBUFSIZE];
#endif
#ifdef CONFIG_ESP32_UART2
static char g_uart2rxbuffer[CONFIG_UART2_RXBUFSIZE];
static char g_uart2txbuffer[CONFIG_UART2_TXBUFSIZE];
#endif

/* This describes the state of the UART0 port. */

#ifdef CONFIG_ESP32_UART0
static const struct esp32_config_s g_uart0config =
{
  .id             = 0,
  .periph         = ESP32_PERIPH_UART,
  .irq            = ESP32_IRQ_UART,
  .txpin          = CONFIG_ESP32_UART0_TXPIN,
  .rxpin          = CONFIG_ESP32_UART0_RXPIN,
  .txsig          = U0TXD_OUT_IDX,
  .rxsig          = U0RXD_IN_IDX,
#ifdef CONFIG_SERIAL_IFLOWCONTROL
  .rtspin         = CONFIG_ESP32_UART0_RTSPIN,
  .rtssig         = U0RTS_OUT_IDX,
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
  .ctspin         = CONFIG_ESP32_UART0_CTSPIN,
  .ctssig         = U0CTS_IN_IDX,
#endif
#ifdef CONFIG_SERIAL_TXDMA
#ifdef CONFIG_ESP32_UART0_TXDMA
  .dma_chan       = UART0_DMA,
#if UART0_DMA == 0
  .dma_sem        = &g_dma0_sem,
#else
  .dma_sem        = &g_dma1_sem,
#endif
#endif
#endif
#ifdef CONFIG_ESP32_UART0_RS485
  .rs485_dir_gpio = CONFIG_ESP32_UART0_RS485_DIR_PIN,
#if (CONFIG_ESP32_UART0_RS485_DIR_POLARITY == 0)
  .rs485_dir_polarity = false,
#else
  .rs485_dir_polarity = true,
#endif
#endif
};

static struct esp32_dev_s g_uart0priv =
{
  .config         = &g_uart0config,
  .baud           = CONFIG_UART0_BAUD,
  .parity         = CONFIG_UART0_PARITY,
  .bits           = CONFIG_UART0_BITS,
  .stopbits2      = CONFIG_UART0_2STOP,
#ifdef CONFIG_SERIAL_TXDMA
#  ifdef CONFIG_ESP32_UART0_TXDMA
  .txdma          = true,    /* TX DMA enabled for this UART */
#  else
  .txdma          = false,   /* TX DMA disabled for this UART */
#  endif
#endif
#ifdef CONFIG_SERIAL_IFLOWCONTROL
#  ifdef CONFIG_UART0_IFLOWCONTROL
  .iflow          = true,    /* Input flow control (RTS) enabled */
#  else
  .iflow          = false,   /* Input flow control (RTS) disabled */
#  endif
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
#  ifdef CONFIG_UART0_OFLOWCONTROL
  .oflow          = true,    /* Output flow control (CTS) enabled */
#  else
  .oflow          = false,   /* Output flow control (CTS) disabled */
#  endif
#endif
};

static uart_dev_t g_uart0port =
{
  .recv     =
  {
    .size   = CONFIG_UART0_RXBUFSIZE,
    .buffer = g_uart0rxbuffer,
  },
  .xmit     =
  {
    .size   = CONFIG_UART0_TXBUFSIZE,
    .buffer = g_uart0txbuffer,
  },
  .ops      = &g_uart_ops,
  .priv     = &g_uart0priv,
};
#endif

/* This describes the state of the UART1 port. */

#ifdef CONFIG_ESP32_UART1
static const struct esp32_config_s g_uart1config =
{
  .id             = 1,
  .periph         = ESP32_PERIPH_UART1,
  .irq            = ESP32_IRQ_UART1,
  .txpin          = CONFIG_ESP32_UART1_TXPIN,
  .rxpin          = CONFIG_ESP32_UART1_RXPIN,
  .txsig          = U1TXD_OUT_IDX,
  .rxsig          = U1RXD_IN_IDX,
#ifdef CONFIG_SERIAL_IFLOWCONTROL
  .rtspin         = CONFIG_ESP32_UART1_RTSPIN,
  .rtssig         = U1RTS_OUT_IDX,
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
  .ctspin         = CONFIG_ESP32_UART1_CTSPIN,
  .ctssig         = U1CTS_IN_IDX,
#endif
#ifdef CONFIG_SERIAL_TXDMA
#  ifdef CONFIG_ESP32_UART1_TXDMA
  .dma_chan       = UART1_DMA,
#    if UART1_DMA == 0
  .dma_sem        = &g_dma0_sem,
#    else
  .dma_sem        = &g_dma1_sem,
#    endif
#  endif
#endif
#ifdef CONFIG_ESP32_UART1_RS485
  .rs485_dir_gpio = CONFIG_ESP32_UART1_RS485_DIR_PIN,
#  if (CONFIG_ESP32_UART1_RS485_DIR_POLARITY == 0)
  .rs485_dir_polarity = false,
#  else
  .rs485_dir_polarity = true,
#  endif
#endif
};

static struct esp32_dev_s g_uart1priv =
{
  .config         = &g_uart1config,
  .baud           = CONFIG_UART1_BAUD,
  .parity         = CONFIG_UART1_PARITY,
  .bits           = CONFIG_UART1_BITS,
  .stopbits2      = CONFIG_UART1_2STOP,
#ifdef CONFIG_SERIAL_TXDMA
#  ifdef CONFIG_ESP32_UART1_TXDMA
  .txdma          = true,    /* TX DMA enabled for this UART */
#  else
  .txdma          = false,   /* TX DMA disabled for this UART */
#  endif
#endif
#ifdef CONFIG_SERIAL_IFLOWCONTROL
#  ifdef CONFIG_UART1_IFLOWCONTROL
  .iflow          = true,    /* input flow control (RTS) enabled */
#  else
  .iflow          = false,   /* input flow control (RTS) disabled */
#  endif
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
#  ifdef CONFIG_UART1_OFLOWCONTROL
  .oflow          = true,    /* output flow control (CTS) enabled */
#  else
  .oflow          = false,   /* output flow control (CTS) disabled */
#  endif
#endif
};

static uart_dev_t g_uart1port =
{
  .recv     =
  {
    .size   = CONFIG_UART1_RXBUFSIZE,
    .buffer = g_uart1rxbuffer,
  },
  .xmit     =
  {
    .size   = CONFIG_UART1_TXBUFSIZE,
    .buffer = g_uart1txbuffer,
  },
  .ops      = &g_uart_ops,
  .priv     = &g_uart1priv,
};
#endif

/* This describes the state of the UART2 port. */

#ifdef CONFIG_ESP32_UART2
static const struct esp32_config_s g_uart2config =
{
  .id             = 2,
  .periph         = ESP32_PERIPH_UART2,
  .irq            = ESP32_IRQ_UART2,
  .txpin          = CONFIG_ESP32_UART2_TXPIN,
  .rxpin          = CONFIG_ESP32_UART2_RXPIN,
  .txsig          = U2TXD_OUT_IDX,
  .rxsig          = U2RXD_IN_IDX,
#ifdef CONFIG_SERIAL_IFLOWCONTROL
  .rtspin         = CONFIG_ESP32_UART2_RTSPIN,
  .rtssig         = U2RTS_OUT_IDX,
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
  .ctspin         = CONFIG_ESP32_UART2_CTSPIN,
  .ctssig         = U2CTS_IN_IDX,
#endif
#ifdef CONFIG_SERIAL_TXDMA
#  ifdef CONFIG_ESP32_UART2_TXDMA
  .dma_chan       = UART2_DMA,
#    if UART2_DMA == 0
  .dma_sem        = &g_dma0_sem,
#    else
  .dma_sem        = &g_dma1_sem,
#    endif
#  endif
#endif
#ifdef CONFIG_ESP32_UART2_RS485
  .rs485_dir_gpio = CONFIG_ESP32_UART2_RS485_DIR_PIN,
#  if (CONFIG_ESP32_UART2_RS485_DIR_POLARITY == 0)
  .rs485_dir_polarity = false,
#  else
  .rs485_dir_polarity = true,
#  endif
#endif
};

static struct esp32_dev_s g_uart2priv =
{
  .config         = &g_uart2config,
  .baud           = CONFIG_UART2_BAUD,
  .parity         = CONFIG_UART2_PARITY,
  .bits           = CONFIG_UART2_BITS,
  .stopbits2      = CONFIG_UART2_2STOP,
#ifdef CONFIG_SERIAL_TXDMA
#  ifdef CONFIG_ESP32_UART2_TXDMA
  .txdma          = true,    /* TX DMA enabled for this UART */
#  else
  .txdma          = false,   /* TX DMA disabled for this UART */
#  endif
#endif
#ifdef CONFIG_SERIAL_IFLOWCONTROL
#  ifdef CONFIG_UART2_IFLOWCONTROL
  .iflow          = true,    /* input flow control (RTS) enabled */
#  else
  .iflow          = false,   /* input flow control (RTS) disabled */
#  endif
#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
#  ifdef CONFIG_UART2_OFLOWCONTROL
  .oflow          = true,    /* output flow control (CTS) enabled */
#  else
  .oflow          = false,   /* output flow control (CTS) disabled */
#  endif
#endif
};

static uart_dev_t g_uart2port =
{
  .recv     =
  {
    .size   = CONFIG_UART2_RXBUFSIZE,
    .buffer = g_uart2rxbuffer,
  },
  .xmit     =
  {
    .size   = CONFIG_UART2_TXBUFSIZE,
    .buffer = g_uart2txbuffer,
  },
  .ops      = &g_uart_ops,
  .priv     = &g_uart2priv,
};
#endif

/****************************************************************************
 * Private Functions
 ****************************************************************************/

#ifdef CONFIG_SERIAL_TXDMA
/****************************************************************************
 * Name: esp32_dmasend
 *
 * Description:
 *   Prepare the descriptor linked-list and initialize a transfer.
 *
 * Parameters:
 *   priv        -  Pointer to the serial driver struct.
 *
 ****************************************************************************/

static void esp32_dmasend(struct uart_dev_s *dev)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

  if (priv->txdma)
    {
      struct esp32_dmadesc_s *dmadesc;
      uint8_t *tp;
#ifdef CONFIG_ESP32_SPIRAM
      uint8_t *alloctp = NULL;
#endif

      /* If the buffer comes from PSRAM, allocate a new one from
       * Internal SRAM.
       */

#ifdef CONFIG_ESP32_SPIRAM
      if (esp32_ptr_extram(dev->dmatx.buffer))
        {
#  ifdef CONFIG_MM_KERNEL_HEAP
          alloctp = kmm_malloc(dev->dmatx.length);
#  elif defined(CONFIG_XTENSA_IMEM_USE_SEPARATE_HEAP)
          alloctp = xtensa_imm_malloc(dev->dmatx.length);
#  endif

          DEBUGASSERT(alloctp != NULL);
          memcpy(alloctp, dev->dmatx.buffer, dev->dmatx.length);
          tp = alloctp;
        }
      else
#endif
        {
          tp = (uint8_t *)dev->dmatx.buffer;
        }

      /* Initialize descriptor linked-list.
       * esp32_dma_init divides the buffer into the list, perform
       * the required alignment and fill all descriptor words.
       */

      dmadesc = s_dma_txdesc[priv->config->dma_chan];

      esp32_dma_init(dmadesc, UART_DMADESC_NUM, tp,
                    (uint32_t) dev->dmatx.length);

      /* Set the 1st descriptor address */

      modifyreg32(UHCI_DMA_OUT_LINK_REG(priv->config->dma_chan),
                  UHCI_OUTLINK_ADDR_M,
                  (((uintptr_t) dmadesc) & UHCI_OUTLINK_ADDR_M));

      /* Trigger DMA transfer */

      modifyreg32(UHCI_DMA_OUT_LINK_REG(priv->config->dma_chan),
                  UHCI_OUTLINK_STOP_M, UHCI_OUTLINK_START_M);

#ifdef CONFIG_ESP32_SPIRAM
      if (alloctp != NULL)
        {
#  ifdef CONFIG_MM_KERNEL_HEAP
          kmm_free(alloctp);
#  elif defined(CONFIG_XTENSA_IMEM_USE_SEPARATE_HEAP)
          xtensa_imm_free(alloctp);
#  endif
        }
#endif
    }
}

/****************************************************************************
 * Name: esp32_dmatxavail
 *
 * Description:
 *   Verifies if the DMA is available for a transfer. If so, trigger a
 *   transfer.
 *
 * Parameters:
 *   priv        -  Pointer to the serial driver struct.
 *
 ****************************************************************************/

static void esp32_dmatxavail(struct uart_dev_s *dev)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

  /* Check if this UART instance has DMA TX enabled */

  if (priv->txdma)
    {
      /* Try to acquire the semaphore.
       * This semaphore is always unlocked at 1st time.
       * Then, the next times, it is released when a DMA transfer
       * is completed.
       */

      if (nxsem_trywait(priv->config->dma_sem) == OK)
        {
          if (priv->config->dma_chan == 0)
            {
              modifyreg32(DPORT_PERIP_CLK_EN_REG, 0, DPORT_UHCI0_CLK_EN);
            }
          else
            {
              modifyreg32(DPORT_PERIP_CLK_EN_REG, 0, DPORT_UHCI1_CLK_EN);
            }

          modifyreg32(UHCI_CONF0_REG(priv->config->dma_chan),
                      UHCI_UART0_CE | UHCI_UART1_CE | UHCI_UART2_CE,
                      1 << (UART_SELECT_SHIFT + priv->config->id));
          dma_enable_int(priv->config->dma_chan);
          uart_xmitchars_dma(dev);
        }
    }
}
#endif

#ifndef CONFIG_SUPPRESS_UART_CONFIG
/****************************************************************************
 * Name: esp32_reset_rx_fifo
 *
 * Description:
 *   Resets the RX FIFO.
 *   NOTE: We can not use rxfifo_rst to reset the hardware RX FIFO.
 *
 * Parameters:
 *   priv        -  Pointer to the serial driver struct.
 *
 ****************************************************************************/

static void esp32_reset_rx_fifo(struct esp32_dev_s *priv)
{
  uint32_t rx_status_reg = getreg32(UART_STATUS_REG(priv->config->id));
  uint32_t fifo_cnt = REG_MASK(rx_status_reg, UART_RXFIFO_CNT);
  uint32_t mem_rx_status_reg = getreg32(UART_MEM_RX_STATUS_REG
                                        (priv->config->id));
  uint32_t rd_address = REG_MASK(mem_rx_status_reg, UART_RD_ADDRESS);
  uint32_t wr_address = REG_MASK(mem_rx_status_reg, UART_WR_ADDRESS);

  while ((fifo_cnt != 0) || (rd_address != wr_address))
    {
      getreg32(DR_UART_FIFO_REG(priv->config->id));

      rx_status_reg = getreg32(UART_STATUS_REG(priv->config->id));
      fifo_cnt = REG_MASK(rx_status_reg, UART_RXFIFO_CNT);
      mem_rx_status_reg = getreg32(UART_MEM_RX_STATUS_REG(priv->config->id));
      rd_address = REG_MASK(mem_rx_status_reg, UART_RD_ADDRESS);
      wr_address = REG_MASK(mem_rx_status_reg, UART_WR_ADDRESS);
    }
}

#endif

/****************************************************************************
 * Name: esp32_get_rx_fifo_len
 *
 * Description:
 *   Get the real value on rx fixo.
 *   RX_FIFO_CNT shouldn't be used alone accordingly to:
 *   https://www.espressif.com/sites/default/files/documentation/eco_
 *   and_workarounds_for_bugs_in_esp32_en.pdf.
 *   So, some arithmetic with the read and write RX FIFO pointers are
 *   necessary.
 *
 * Parameters:
 *   priv        -  Pointer to the serial driver struct.
 *
 * Return:
 *   The number of bytes in RX fifo.
 *
 ****************************************************************************/

static uint32_t esp32_get_rx_fifo_len(struct esp32_dev_s *priv)
{
  uint32_t rd_address;
  uint32_t wr_address;
  uint32_t fifo_cnt;
  uint32_t mem_rx_status_reg;
  uint32_t rx_status_reg;
  uint32_t len;

  mem_rx_status_reg = getreg32(UART_MEM_RX_STATUS_REG(priv->config->id));
  rd_address = REG_MASK(mem_rx_status_reg, UART_RD_ADDRESS);
  wr_address = REG_MASK(mem_rx_status_reg, UART_WR_ADDRESS);
  rx_status_reg = getreg32(UART_STATUS_REG(priv->config->id));
  fifo_cnt = REG_MASK(rx_status_reg, UART_RXFIFO_CNT);

  if (wr_address > rd_address)
    {
      len = wr_address - rd_address;
    }
  else if (wr_address < rd_address)
    {
      len = (wr_address + 128) - rd_address;
    }
  else
    {
      len = fifo_cnt > 0 ? 128 : 0;
    }

  return len;
}

/****************************************************************************
 * Name: esp32_restoreuartint
 ****************************************************************************/

static inline void esp32_restoreuartint(struct esp32_dev_s *priv,
                                        uint32_t intena)
{
  /* Restore the previous interrupt state
   * (assuming all interrupts disabled)
   */

  putreg32(intena, UART_INT_ENA_REG(priv->config->id));
}

/****************************************************************************
 * Name: esp32_disableallints
 ****************************************************************************/

static void esp32_disableallints(struct esp32_dev_s *priv, uint32_t *intena)
{
  irqstate_t flags;

  /* The following must be atomic */

  flags = spin_lock_irqsave(&priv->lock);

  if (intena)
    {
      /* Return the current interrupt mask */

      *intena = getreg32(UART_INT_ENA_REG(priv->config->id));
    }

  /* Disable all interrupts */

  putreg32(0, UART_INT_ENA_REG(priv->config->id));
  spin_unlock_irqrestore(&priv->lock, flags);
}

/****************************************************************************
 * Name: esp32_setup
 *
 * Description:
 *   Configure the UART baud, bits, parity, etc. This method is called the
 *   first time that the serial port is opened.
 *
 ****************************************************************************/

static int esp32_setup(struct uart_dev_s *dev)
{
#ifndef CONFIG_SUPPRESS_UART_CONFIG
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
  uint32_t clkdiv;
  uint32_t regval;
  uint32_t conf0;

  /* Note: The logic here depends on the fact that that the UART module
   * was enabled and the pins were configured in esp32_lowsetup().
   */

  /* The shutdown method will put the UART in a known, disabled state */

  esp32_shutdown(dev);

  /* Set up the CONF0 register. */

  conf0 = UART_TICK_REF_ALWAYS_ON | UART_ERR_WR_MASK_M;

#ifdef CONFIG_SERIAL_OFLOWCONTROL
  /* Check if output flow control is enabled for this UART controller. */

  if (priv->oflow)
    {
      /* Enable output hardware flow control */

      conf0 |= UART_TX_FLOW_EN;
    }

#endif

  /* OR in settings for the selected number of bits */

  if (priv->bits == 5)
    {
      /* 0=5 bits */
    }
  else if (priv->bits == 6)
    {
      conf0 |= (1 << UART_BIT_NUM_S);  /* 1=6 bits */
    }
  else if (priv->bits == 7)
    {
      conf0 |= (2 << UART_BIT_NUM_S);  /* 2=7 bits */
    }
  else /* if (priv->bits == 8) */
    {
      conf0 |= (3 << UART_BIT_NUM_S);  /* 3=8 bits */
    }

  /* OR in settings for the selected parity */

  if (priv->parity == 1)
    {
      conf0 |= UART_PARITY_EN;
    }
  else if (priv->parity == 2)
    {
      conf0 |= UART_PARITY_EN | UART_PARITY;
    }

  /* OR in settings for the number of stop bits */

  if (priv->stopbits2)
    {
      conf0 |= 2 << UART_STOP_BIT_NUM_S;
    }
  else
    {
      conf0 |= 1 << UART_STOP_BIT_NUM_S;
    }

  /* Configure the UART BAUD */

  clkdiv  = (UART_CLK_FREQ << 4) / priv->baud;

  regval  = (clkdiv >> 4) << UART_CLKDIV_S;
  regval |= (clkdiv & 15) << UART_CLKDIV_FRAG_S;
  putreg32(regval, UART_CLKDIV_REG(priv->config->id));

  /* Reset the RX and TX FIFO */

  esp32_reset_rx_fifo(priv);

  /* Configure and enable the UART */

  putreg32(conf0, UART_CONF0_REG(priv->config->id));
  regval = VALUE_TO_FIELD(UART_RX_FIFO_FULL_THRHD, UART_RXFIFO_FULL_THRHD) |
           VALUE_TO_FIELD(UART_RX_TOUT_THRHD_VALUE, UART_RX_TOUT_THRHD) |
           UART_RX_TOUT_EN;
  putreg32(regval, UART_CONF1_REG(priv->config->id));

  /* Enable RX and error interrupts.  Clear and pending interrtupt */

  regval = UART_RXFIFO_FULL_INT_ENA | UART_FRM_ERR_INT_ENA |
           UART_RXFIFO_TOUT_INT_ENA;
  putreg32(regval, UART_INT_ENA_REG(priv->config->id));

  putreg32(UINT32_MAX, UART_INT_CLR_REG(priv->config->id));

#ifdef CONFIG_SERIAL_IFLOWCONTROL
  /* Check if input flow control is enabled for this UART controller */

  if (priv->iflow)
    {
      /* Enable input hardware flow control */

      regval |= VALUE_TO_FIELD(UART_RX_FLOW_THRHD_VALUE, UART_RX_FLOW_THRHD)
                | UART_RX_FLOW_EN;
      modifyreg32(UART_CONF1_REG(priv->config->id), 0, regval);
    }

#endif

#endif
  return OK;
}

/****************************************************************************
 * Name: esp32_shutdown
 *
 * Description:
 *   Disable the UART.  This method is called when the serial port is
 *   closed.  It is assumed that esp32_detach was called earlier in the
 *   shutdown sequence.
 *
 ****************************************************************************/

static void esp32_shutdown(struct uart_dev_s *dev)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
  uint32_t status;

  /* Wait for outgoing FIFO to clear.   The ROM bootloader does not flush
   * the FIFO before handing over to user code, so some of this output is
   * not currently seen when the UART is reconfigured in early stages of
   * startup.
   */

  do
    {
      status = getreg32(UART_STATUS_REG(priv->config->id));
    }
  while ((status & UART_TXFIFO_CNT_M) != 0);

  /* Disable all UART interrupts */

  esp32_disableallints(priv, NULL);
  putreg32(UINT32_MAX, UART_INT_CLR_REG(priv->config->id));
}

/****************************************************************************
 * Name: esp32_attach
 *
 * Description:
 *   Configure the UART to operation in interrupt driven mode.  This method
 *   is called when the serial port is opened.  Normally, this is just after
 *   the the setup() method is called, however, the serial console may
 *   operate in a non-interrupt driven mode during the boot phase.
 *
 *   RX and TX interrupts are not enabled when by the attach method (unless
 *   the hardware supports multiple levels of interrupt enabling).  The RX
 *   and TX interrupts are not enabled until the txint() and rxint() methods
 *   are called.
 *
 ****************************************************************************/

static int esp32_attach(struct uart_dev_s *dev)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
  int ret = OK;

  /* Set up to receive peripheral interrupts on the current CPU */

  priv->cpu = this_cpu();
  priv->cpuint = esp32_setup_irq(priv->cpu, priv->config->periph,
                                 1, ESP32_CPUINT_LEVEL);
  if (priv->cpuint < 0)
    {
      /* Failed to allocate a CPU interrupt of this type */

      return priv->cpuint;
    }

  /* Attach and enable the IRQ */

  ret = irq_attach(priv->config->irq, esp32_interrupt, dev);
  if (ret == OK)
    {
      /* Enable the CPU interrupt (RX and TX interrupts are still disabled
       * in the UART
       */

      up_enable_irq(priv->config->irq);
    }

  return ret;
}

/****************************************************************************
 * Name: esp32_detach
 *
 * Description:
 *   Detach UART interrupts.  This method is called when the serial port is
 *   closed normally just before the shutdown method is called.  The
 *   exception is the serial console which is never shutdown.
 *
 ****************************************************************************/

static void esp32_detach(struct uart_dev_s *dev)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

  /* Disable and detach the CPU interrupt */

  up_disable_irq(priv->config->irq);
  irq_detach(priv->config->irq);

  /* Disassociate the peripheral interrupt from the CPU interrupt */

  esp32_teardown_irq(priv->cpu, priv->config->periph, priv->cpuint);
  priv->cpuint = -1;
}

#ifdef CONFIG_SERIAL_TXDMA

/****************************************************************************
 * Name: dma_enable_int
 *
 * Description:
 *   Enable UHCI interrupt.
 *
 * Parameters:
 *   dma_chan - DMA instance.
 *
 ****************************************************************************/

static inline void dma_enable_int(uint8_t dma_chan)
{
  /* Interrupt will be triggered when all descriptors were transferred or
   * in case of error with output descriptor.
   */

  uint32_t int_mask = UHCI_OUT_TOTAL_EOF_INT_ENA_M |
                      UHCI_OUT_DSCR_ERR_INT_ENA_M;
  putreg32(int_mask, UHCI_INT_ENA_REG(dma_chan));
}

/****************************************************************************
 * Name: dma_disable_int.
 *
 * Description:
 *   Disable UHCI interrupt.
 *
 * Parameters:
 *   dma_chan - DMA instance.
 *
 ****************************************************************************/

static inline void dma_disable_int(uint8_t dma_chan)
{
  putreg32(0, UHCI_INT_ENA_REG(dma_chan));
}

/****************************************************************************
 * Name: dma_attach
 *
 * Description:
 *   Configure an DMA interrupt, attach to a CPU interrupt and enable it.
 *
 * Parameters:
 *   dma_chan - DMA instance.
 *
 ****************************************************************************/

static void dma_attach(uint8_t dma_chan)
{
  int dma_cpuint;
  int cpu;
  int ret;
  int periph;
  int irq;

  /* Clear the interrupts */

  putreg32(UINT32_MAX, UHCI_INT_CLR_REG(dma_chan));

  /* Attach the UHCI interrupt to the allocated CPU interrupt
   * and attach and enable the IRQ.
   */

  if (dma_chan == 0)
    {
      periph = ESP32_PERIPH_UHCI0;
      irq = ESP32_IRQ_UHCI0;
    }
  else
    {
      periph = ESP32_PERIPH_UHCI1;
      irq = ESP32_IRQ_UHCI1;
    }

  /* Set up to receive peripheral interrupts on the current CPU */

  cpu = this_cpu();
  dma_cpuint = esp32_setup_irq(cpu, periph, 1, ESP32_CPUINT_LEVEL);
  if (dma_cpuint < 0)
    {
      /* Failed to allocate a CPU interrupt of this type */

      dmaerr("Failed to allocate a CPU interrupt.\n");
      return;
    }

  ret = irq_attach(irq, esp32_interrupt_dma, NULL);
  if (ret == OK)
    {
      /* Enable the CPU interrupt */

      up_enable_irq(irq);
    }
  else
    {
      dmaerr("Couldn't attach IRQ to handler.\n");
    }
}

/****************************************************************************
 * Name: esp32_interrupt
 *
 * Description:
 *   DMA interrupt.
 *
 ****************************************************************************/

static int esp32_interrupt_dma(int irq, void *context, void *arg)
{
  uint32_t value;
  uint32_t status;
  uint8_t uhci = irq - ESP32_IRQ_UHCI0;
  struct uart_dev_s *dev = NULL;

  /* Disable interrupt, stop UHCI, save interrupt status
   * clear interrupts.
   */

  status = getreg32(UHCI_INT_ST_REG(uhci));
  dma_disable_int(uhci);
  modifyreg32(UHCI_DMA_OUT_LINK_REG(uhci),
              UHCI_OUTLINK_START_M, UHCI_OUTLINK_STOP_M);
  putreg32(UINT32_MAX, UHCI_INT_CLR_REG(uhci));

  /* Check which UART is using DMA now and calls
   * uart_xmitchars_done to adjust TX software buffer.
   */

  value = getreg32(UHCI_CONF0_REG(uhci));
  value = value & (UHCI_UART2_CE_M | UHCI_UART1_CE_M | UHCI_UART0_CE_M);

  switch (value)
    {
#  ifdef CONFIG_ESP32_UART0_TXDMA
      case UHCI_UART0_CE_M:
        dev = &g_uart0port;
      break;
#  endif

#  ifdef CONFIG_ESP32_UART1_TXDMA
      case UHCI_UART1_CE_M:
        dev = &g_uart1port;
      break;
#  endif

#  ifdef CONFIG_ESP32_UART2_TXDMA
      case UHCI_UART2_CE_M:
        dev = &g_uart2port;
      break;
#  endif

      default:
        dmaerr("No UART selected\n");
    }

  if (dev != NULL)
    {
      dev->dmatx.nbytes = dev->dmatx.length;
      uart_xmitchars_done(dev);
    }

  /* Post on semaphore to allow new transfers and share the resource.
   * Disable clk gate for UHCI, so RX can work properly.
   */

  if (status & UHCI_OUT_TOTAL_EOF_INT_ENA_M)
    {
      if (uhci == 0)
        {
          nxsem_post(&g_dma0_sem);
          modifyreg32(DPORT_PERIP_CLK_EN_REG, DPORT_UHCI0_CLK_EN, 0);
        }
#  ifdef USE_DMA1
      else
        {
          nxsem_post(&g_dma1_sem);
          modifyreg32(DPORT_PERIP_CLK_EN_REG, DPORT_UHCI1_CLK_EN, 0);
        }
#  endif
    }
  else
    {
      dmaerr("Error with the output descriptor in DMA 0\n");
    }

  return OK;
}

/****************************************************************************
 * Name: dma_config
 *
 * Description:
 *   Configure the UHCI peripheral.
 *
 * Parameters:
 *   dma_chan - DMA instance.
 *
 ****************************************************************************/

static void dma_config(uint8_t dma_chan)
{
  /* Enable peripheral CLK and RST module */

  if (dma_chan == 0)
    {
      modifyreg32(DPORT_PERIP_CLK_EN_REG, 0, DPORT_UHCI0_CLK_EN);
      modifyreg32(DPORT_PERIP_RST_EN_REG, DPORT_UHCI0_RST, DPORT_UHCI0_RST);
      modifyreg32(DPORT_PERIP_RST_EN_REG, DPORT_UHCI0_RST, 0);
    }
  else
    {
      modifyreg32(DPORT_PERIP_CLK_EN_REG, 0, DPORT_UHCI1_CLK_EN);
      modifyreg32(DPORT_PERIP_RST_EN_REG, DPORT_UHCI1_RST, DPORT_UHCI1_RST);
      modifyreg32(DPORT_PERIP_RST_EN_REG, DPORT_UHCI1_RST, 0);
    }

  /* Configure registers */

  putreg32(UHCI_CLK_EN_M, UHCI_CONF0_REG(dma_chan));

  putreg32(0, UHCI_CONF1_REG(dma_chan));
  putreg32(UHCI_CHECK_OWNER | (100 << UHCI_DMA_INFIFO_FULL_THRS_S),
           UHCI_CONF1_REG(dma_chan));

  putreg32(0, UHCI_HUNG_CONF_REG(dma_chan));

  modifyreg32(UHCI_CONF0_REG(dma_chan), UHCI_IN_RST, UHCI_IN_RST);
  modifyreg32(UHCI_CONF0_REG(dma_chan), UHCI_IN_RST, 0);
  modifyreg32(UHCI_CONF0_REG(dma_chan), UHCI_OUT_RST, UHCI_OUT_RST);
  modifyreg32(UHCI_CONF0_REG(dma_chan), UHCI_OUT_RST, 0);
}
#endif

/****************************************************************************
 * Name: esp32_interrupt
 *
 * Description:
 *   This is the common UART interrupt handler.  It will be invoked when an
 *   interrupt is received on the 'irq'.  It should call uart_xmitchars or
 *   uart_recvchars to perform the appropriate data transfers.  The
 *   interrupt handling logic must be able to map the 'arg' to the
 *   appropriate uart_dev_s structure in order to call these functions.
 *
 ****************************************************************************/

static int esp32_interrupt(int cpuint, void *context, void *arg)
{
  struct uart_dev_s *dev = (struct uart_dev_s *)arg;
  struct esp32_dev_s *priv;
  uint32_t regval;
  uint32_t status;
  uint32_t enabled;
  unsigned int nfifo;
  int passes;
  bool handled;

  DEBUGASSERT(dev != NULL && dev->priv != NULL);
  priv = (struct esp32_dev_s *)dev->priv;

  /* Loop until there are no characters to be transferred or, until we have
   * been looping for a long time.
   */

  handled = true;
  for (passes = 0; passes < 256 && handled; passes++)
    {
      handled      = false;
      priv->status = getreg32(UART_INT_RAW_REG(priv->config->id));
      status       = getreg32(UART_STATUS_REG(priv->config->id));
      enabled      = getreg32(UART_INT_ENA_REG(priv->config->id));

      /* Clear pending interrupts */

      regval = (UART_RXFIFO_FULL_INT_CLR | UART_FRM_ERR_INT_CLR |
                UART_RXFIFO_TOUT_INT_CLR | UART_TX_DONE_INT_CLR |
                UART_TXFIFO_EMPTY_INT_CLR | UART_TX_BRK_IDLE_DONE_INT_CLR);
      putreg32(regval, UART_INT_CLR_REG(priv->config->id));

#ifdef HAVE_RS485
      if ((enabled & UART_TX_BRK_IDLE_DONE_INT_ENA) != 0 &&
          (status & UART_TX_DONE_INT_ST) != 0)
        {
          /* If all bytes were transmitted, then we can disable the RS485
           * transmit (TX/nTX) pin.
           */

          nfifo = REG_MASK(status, UART_TXFIFO_CNT);
          if (nfifo == 0)
            {
              esp32_gpiowrite(priv->config->rs485_dir_gpio,
                              !priv->config->rs485_dir_polarity);
            }
        }
#endif

      /* Are Rx interrupts enabled?  The upper layer may hold off Rx input
       * by disabling the Rx interrupts if there is no place to saved the
       * data, possibly resulting in an overrun error.
       */

      if ((enabled & (UART_RXFIFO_FULL_INT_ENA |
                      UART_RXFIFO_TOUT_INT_ENA)) != 0)
        {
          /* Is there any data waiting in the Rx FIFO? */

          nfifo = esp32_get_rx_fifo_len(priv);
          if (nfifo > 0)
            {
              /* Received data in the RXFIFO! ... Process incoming bytes */

              uart_recvchars(dev);
              handled = true;
            }
        }

      /* Are Tx interrupts enabled?  The upper layer will disable Tx
       * interrupts when it has nothing to send.
       */

      if ((enabled & (UART_TX_DONE_INT_ENA | UART_TXFIFO_EMPTY_INT_ENA))
          != 0)
        {
          nfifo = REG_MASK(status, UART_TXFIFO_CNT);
          if (nfifo < 0x7f)
            {
              /* The TXFIFO is not full ... process outgoing bytes */

              uart_xmitchars(dev);
              handled = true;
            }
        }
    }

  return OK;
}

/****************************************************************************
 * Name: esp32_ioctl
 *
 * Description:
 *   All ioctl calls will be routed through this method
 *
 ****************************************************************************/

static int esp32_ioctl(struct file *filep, int cmd, unsigned long arg)
{
#if defined(CONFIG_SERIAL_TERMIOS) || defined(CONFIG_SERIAL_TIOCSERGSTRUCT)
  struct inode      *inode = filep->f_inode;
  struct uart_dev_s *dev   = inode->i_private;
#endif
  int                ret    = OK;

  switch (cmd)
    {
#ifdef CONFIG_SERIAL_TIOCSERGSTRUCT
    case TIOCSERGSTRUCT:
      {
         struct esp32_dev_s *user = (struct esp32_dev_s *)arg;
         if (!user)
           {
             ret = -EINVAL;
           }
         else
           {
             memcpy(user, dev, sizeof(struct esp32_dev_s));
           }
       }
       break;
#endif

#ifdef CONFIG_SERIAL_TERMIOS
    case TCGETS:
      {
        struct termios *termiosp = (struct termios *)arg;
        struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

        if (!termiosp)
          {
            ret = -EINVAL;
            break;
          }

        /* Return parity */

        termiosp->c_cflag = ((priv->parity != 0) ? PARENB : 0) |
                            ((priv->parity == 1) ? PARODD : 0);

        /* Return stop bits */

        termiosp->c_cflag |= (priv->stopbits2) ? CSTOPB : 0;

        /* Return flow control */

#  ifdef CONFIG_SERIAL_OFLOWCONTROL
        termiosp->c_cflag |= (priv->oflow) ? CCTS_OFLOW : 0;
#  endif
#  ifdef CONFIG_SERIAL_IFLOWCONTROL
        termiosp->c_cflag |= (priv->iflow) ? CRTS_IFLOW : 0;
#  endif
        /* Return baud */

        cfsetispeed(termiosp, priv->baud);

        /* Return number of bits */

        switch (priv->bits)
          {
          case 5:
            termiosp->c_cflag |= CS5;
            break;

          case 6:
            termiosp->c_cflag |= CS6;
            break;

          case 7:
            termiosp->c_cflag |= CS7;
            break;

          default:
          case 8:
            termiosp->c_cflag |= CS8;
            break;

          case 9:
            termiosp->c_cflag |= CS8 /* CS9 */ ;
            break;
          }
      }
      break;

    case TCSETS:
      {
        struct termios *termiosp = (struct termios *)arg;
        struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
        uint32_t baud;
        uint32_t intena;
        uint8_t parity;
        uint8_t nbits;
        bool stop2;
#  ifdef CONFIG_SERIAL_IFLOWCONTROL
        bool iflow;
#  endif
#  ifdef CONFIG_SERIAL_OFLOWCONTROL
        bool oflow;
#  endif

        if (!termiosp)
          {
            ret = -EINVAL;
            break;
          }

        /* Decode baud. */

        ret = OK;
        baud = cfgetispeed(termiosp);

        /* Decode number of bits */

        switch (termiosp->c_cflag & CSIZE)
          {
          case CS5:
            nbits = 5;
            break;

          case CS6:
            nbits = 6;
            break;

          case CS7:
            nbits = 7;
            break;

          case CS8:
            nbits = 8;
            break;
#  if 0
          case CS9:
            nbits = 9;
            break;
#  endif
          default:
            ret = -EINVAL;
            break;
          }

        /* Decode parity */

        if ((termiosp->c_cflag & PARENB) != 0)
          {
            parity = (termiosp->c_cflag & PARODD) ? 1 : 2;
          }
        else
          {
            parity = 0;
          }

        /* Decode stop bits */

        stop2 = (termiosp->c_cflag & CSTOPB) != 0;

        /* Decode flow control */

#  ifdef CONFIG_SERIAL_IFLOWCONTROL
        iflow = (termiosp->c_cflag &  CRTS_IFLOW) != 0;
#  endif
#  ifdef CONFIG_SERIAL_OFLOWCONTROL
        oflow = (termiosp->c_cflag & CCTS_OFLOW) != 0;
#  endif
        /* Verify that all settings are valid before committing */

        if (ret == OK)
          {
            /* Commit */

            priv->baud      = baud;
            priv->parity    = parity;
            priv->bits      = nbits;
            priv->stopbits2 = stop2;
#  ifdef CONFIG_SERIAL_IFLOWCONTROL
            priv->iflow = iflow;
#  endif
#  ifdef CONFIG_SERIAL_OFLOWCONTROL
            priv->oflow = oflow;
#  endif
            /* effect the changes immediately - note that we do not
             * implement TCSADRAIN / TCSAFLUSH
             */

            esp32_disableallints(priv, &intena);
            ret = esp32_setup(dev);

            /* Restore the interrupt state */

            esp32_restoreuartint(priv, intena);
          }
      }
      break;
#endif /* CONFIG_SERIAL_TERMIOS */

    default:
      ret = -ENOTTY;
      break;
    }

  return ret;
}

/****************************************************************************
 * Name: esp32_receive
 *
 * Description:
 *   Called (usually) from the interrupt level to receive one
 *   character from the UART.  Error bits associated with the
 *   receipt are provided in the return 'status'.
 *
 ****************************************************************************/

static int  esp32_receive(struct uart_dev_s *dev, unsigned int *status)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
  uint32_t rx_fifo;

  /* Return the error information in the saved status */

  *status      = (unsigned int)priv->status;
  priv->status = 0;

  /* Then return the actual received byte */

  rx_fifo = getreg32(DR_UART_FIFO_REG(priv->config->id));

  return (int)REG_MASK(rx_fifo, UART_RXFIFO_RD_BYTE);
}

/****************************************************************************
 * Name: esp32_rxint
 *
 * Description:
 *   Call to enable or disable RXRDY interrupts
 *
 ****************************************************************************/

static void esp32_rxint(struct uart_dev_s *dev, bool enable)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
  irqstate_t flags;
  int regval;

  flags = spin_lock_irqsave(&priv->lock);

  if (enable)
    {
      /* Receive an interrupt when their is anything in the Rx data register
       * (or an Rx timeout occurs).
       */

#ifndef CONFIG_SUPPRESS_SERIAL_INTS
      regval  = getreg32(UART_INT_ENA_REG(priv->config->id));
      regval |= (UART_RXFIFO_FULL_INT_ENA | UART_FRM_ERR_INT_ENA |
                 UART_RXFIFO_TOUT_INT_ENA);
      putreg32(regval, UART_INT_ENA_REG(priv->config->id));
#endif
    }
  else
    {
      /* Disable the RX interrupts */

      regval  = getreg32(UART_INT_ENA_REG(priv->config->id));
      regval &= ~(UART_RXFIFO_FULL_INT_ENA | UART_FRM_ERR_INT_ENA |
                  UART_RXFIFO_TOUT_INT_ENA);
      putreg32(regval, UART_INT_ENA_REG(priv->config->id));
    }

  spin_unlock_irqrestore(&priv->lock, flags);
}

/****************************************************************************
 * Name: esp32_rxavailable
 *
 * Description:
 *   Return true if the receive holding register is not empty
 *
 ****************************************************************************/

static bool esp32_rxavailable(struct uart_dev_s *dev)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
  return esp32_get_rx_fifo_len(priv) > 0;
}

/****************************************************************************
 * Name: esp32_send
 *
 * Description:
 *   This method will send one byte on the UART.
 *
 ****************************************************************************/

static void esp32_send(struct uart_dev_s *dev, int ch)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

#ifdef HAVE_RS485
  if (priv->config->rs485_dir_gpio != 0)
    {
      esp32_gpiowrite(priv->config->rs485_dir_gpio,
                      priv->config->rs485_dir_polarity);
    }
#endif

  putreg32((uint32_t)ch, AHB_UART_FIFO_REG(priv->config->id));
}

/****************************************************************************
 * Name: esp32_txint
 *
 * Description:
 *   Call to enable or disable TX interrupts
 *
 ****************************************************************************/

static void esp32_txint(struct uart_dev_s *dev, bool enable)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
  irqstate_t flags;
#ifdef CONFIG_SERIAL_TXDMA
  if (priv->txdma == false)
    {
#endif
      flags = spin_lock_irqsave(&priv->lock);

      if (enable)
        {
          /* After all bytes physically transmitted in the RS485 bus
           * the TX_BRK_IDLE will indicate we can disable the TX pin.
           */

#ifdef HAVE_RS485
          if (priv->config->rs485_dir_gpio != 0)
            {
              modifyreg32(UART_INT_ENA_REG(priv->config->id),
                          0, UART_TX_BRK_IDLE_DONE_INT_ENA);
            }
#endif

          /* Set to receive an interrupt when the TX holding register
           * is empty.
           */

#ifndef CONFIG_SUPPRESS_SERIAL_INTS
          modifyreg32(UART_INT_ENA_REG(priv->config->id),
                      0, (UART_TX_DONE_INT_ENA | UART_TXFIFO_EMPTY_INT_ENA));

#else
          /* Fake a TX interrupt here by just calling uart_xmitchars() with
           * interrupts disabled (note this may recurse).
           */

          spin_unlock_irqrestore(&priv->lock, flags);
          uart_xmitchars(dev);
#endif
        }
      else
        {
          /* Disable the TX interrupt */

          modifyreg32(UART_INT_ENA_REG(priv->config->id),
                      (UART_TX_DONE_INT_ENA | UART_TXFIFO_EMPTY_INT_ENA), 0);
        }

      spin_unlock_irqrestore(&priv->lock, flags);
#ifdef CONFIG_SERIAL_TXDMA
    }
#endif
}

/****************************************************************************
 * Name: esp32_txready
 *
 * Description:
 *   Return true if the transmit holding register is empty (TXRDY)
 *
 ****************************************************************************/

static bool esp32_txready(struct uart_dev_s *dev)
{
  uint32_t txcnt;
  uint32_t reg;
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

  reg = getreg32(UART_STATUS_REG(priv->config->id));
  txcnt = REG_MASK(reg, UART_TXFIFO_CNT);

  return (txcnt < (UART_TX_FIFO_SIZE - 1));
}

/****************************************************************************
 * Name: esp32_txempty
 *
 * Description:
 *   Return true if the transmit holding and shift registers are empty
 *
 ****************************************************************************/

static bool esp32_txempty(struct uart_dev_s *dev)
{
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

  return ((getreg32(UART_STATUS_REG(priv->config->id))
          & UART_TXFIFO_CNT_M) == 0);
}

#ifndef CONFIG_SUPPRESS_UART_CONFIG
/****************************************************************************
 * Name: esp32_config_pins
 *
 * Description:
 *   Performs the pin configuration.
 *
 * Parameters:
 *   priv        -  Pointer to the serial driver struct.
 *
 ****************************************************************************/

static void esp32_config_pins(struct esp32_dev_s *priv)
{
  /* Configure UART pins
   *
   * Internal signals can be output to multiple GPIO pads.
   * But only one GPIO pad can connect with input signal
   */

  /* Keep TX pin in high level to avoid "?" trash character
   * This "?" is the Unicode replacement character (U+FFFD)
   */

  esp32_gpiowrite(priv->config->txpin, true);
  esp32_configgpio(priv->config->txpin, OUTPUT_FUNCTION_3);
  esp32_gpio_matrix_out(priv->config->txpin, priv->config->txsig, 0, 0);

  esp32_configgpio(priv->config->rxpin, INPUT_FUNCTION_3);
  esp32_gpio_matrix_in(priv->config->rxpin, priv->config->rxsig, 0);

#ifdef CONFIG_SERIAL_IFLOWCONTROL
  if (priv->iflow)
    {
      esp32_configgpio(priv->config->rtspin, OUTPUT_FUNCTION_3);
      esp32_gpio_matrix_out(priv->config->rtspin, priv->config->rtssig,
                            0, 0);
    }

#endif
#ifdef CONFIG_SERIAL_OFLOWCONTROL
  if (priv->oflow)
    {
      esp32_configgpio(priv->config->ctspin, INPUT_FUNCTION_3);
      esp32_gpio_matrix_in(priv->config->ctspin, priv->config->ctssig, 0);
    }
#endif

#ifdef HAVE_RS485
  if (priv->config->rs485_dir_gpio != 0)
    {
      esp32_configgpio(priv->config->rs485_dir_gpio, OUTPUT_FUNCTION_3);
      esp32_gpio_matrix_out(priv->config->rs485_dir_gpio,
                            SIG_GPIO_OUT_IDX, 0, 0);
      esp32_gpiowrite(priv->config->rs485_dir_gpio,
                      !priv->config->rs485_dir_polarity);
    }
#endif
}

/****************************************************************************
 * Name: esp32_rxflowcontrol
 *
 * Description:
 *   Called when upper half RX buffer is full (or exceeds configured
 *   watermark levels if CONFIG_SERIAL_IFLOWCONTROL_WATERMARKS is defined).
 *   Return true if UART activated RX flow control to block more incoming
 *   data.
 *   NOTE: ESP32 has a hardware RX FIFO threshold mechanism to control RTS
 *   line and to stop receiving data. This is very similar to the concept
 *   behind upper watermark level. The hardware threshold is used here
 *   to control the RTS line. When setting the threshold to zero, RTS will
 *   imediately be asserted. If nbuffered = 0 or the lower watermark is
 *   crossed and the serial driver decides to disable RX flow control, the
 *   threshold will be changed to UART_RX_FLOW_THRHD_VALUE, which is almost
 *   half the HW RX FIFO capacity. It keeps some space to keep the data
 *   received after the RTS is asserted, but before the sender stops.
 *
 * Input Parameters:
 *   dev       - UART device instance
 *   nbuffered - the number of characters currently buffered
 *               (if CONFIG_SERIAL_IFLOWCONTROL_WATERMARKS is
 *               not defined the value will be 0 for an empty buffer or the
 *               defined buffer size for a full buffer)
 *   upper     - true indicates the upper watermark was crossed where
 *               false indicates the lower watermark has been crossed
 *
 * Returned Value:
 *   true if RX flow control activated.
 *
 ****************************************************************************/

#ifdef CONFIG_SERIAL_IFLOWCONTROL
static bool esp32_rxflowcontrol(struct uart_dev_s *dev,
                                unsigned int nbuffered, bool upper)
{
  bool ret = false;
  struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;

  if (priv->iflow)
    {
      if (nbuffered == 0 || upper == false)
        {
          uint32_t regval;

          /* Empty buffer, RTS should be de-asserted and logic in above
           * layers should re-enable RX interrupt.
           */

          regval = VALUE_TO_FIELD(UART_RX_FLOW_THRHD_VALUE,
                                  UART_RX_FLOW_THRHD);
          modifyreg32(UART_CONF1_REG(priv->config->id), 0, regval);
          esp32_rxint(dev, true);
          ret = false;
        }
      else
        {
          /* If the RX buffer is not zero and watermarks are not enabled,
           * then this function is called to announce RX buffer is full.
           * The first thing it should do is to imediately assert RTS.
           */

          modifyreg32(UART_CONF1_REG(priv->config->id), UART_RX_FLOW_THRHD_M,
                      0);

          /* Software RX FIFO is full, so besides asserting RTS, it's
           * necessary to disable RX interrupts to prevent remaining bytes
           * (that arrive after asserting RTS) to be pushed to the
           * SW RX FIFO.
           */

           esp32_rxint(dev, false);
           ret = true;
        }
    }

  return ret;
}
#endif

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: esp32_lowsetup
 *
 * Description:
 *   Performs the pin configuration for all UARTs.
 *   This functions is intended to be called in the __start function.
 *
 ****************************************************************************/

void esp32_lowsetup(void)
{
  esp32_config_pins(TTYS0_DEV.priv);
#ifdef TTYS1_DEV
  esp32_config_pins(TTYS1_DEV.priv);
#endif
#ifdef TTYS2_DEV
  esp32_config_pins(TTYS2_DEV.priv);
#endif
}

#endif /* CONFIG_SUPPRESS_UART_CONFIG */
/****************************************************************************
 * Name: xtensa_early_serial_initialize
 *
 * Description:
 *   Performs the low level UART initialization early in debug so that the
 *   serial console will be available during bootup.  This must be called
 *   before xtensa_serialinit.
 *
 ****************************************************************************/

#ifdef USE_EARLYSERIALINIT
void xtensa_earlyserialinit(void)
{
  /* NOTE:  All GPIO configuration for the UARTs was performed in
   * esp32_lowsetup
   */

  /* Disable all UARTS */

  esp32_disableallints(TTYS0_DEV.priv, NULL);
#ifdef TTYS1_DEV
  esp32_disableallints(TTYS1_DEV.priv, NULL);
#endif
#ifdef TTYS2_DEV
  esp32_disableallints(TTYS2_DEV.priv, NULL);
#endif

  /* Configuration whichever one is the console */

#ifdef HAVE_SERIAL_CONSOLE
  CONSOLE_DEV.isconsole = true;
  esp32_setup(&CONSOLE_DEV);
#endif
}
#endif

/****************************************************************************
 * Name: xtensa_serial_initialize
 *
 * Description:
 *   Register serial console and serial ports.  This assumes
 *   that xtensa_earlyserialinit was called previously.
 *
 ****************************************************************************/

void xtensa_serialinit(void)
{
  /* Register the console */

#ifdef HAVE_SERIAL_CONSOLE
  uart_register("/dev/console", &CONSOLE_DEV);
#endif

  /* Register all UARTs */

  uart_register("/dev/ttyS0", &TTYS0_DEV);
#ifdef TTYS1_DEV
  uart_register("/dev/ttyS1", &TTYS1_DEV);
#endif
#ifdef TTYS2_DEV
  uart_register("/dev/ttyS2", &TTYS2_DEV);
#endif

  /* DMA related */

#ifdef CONFIG_SERIAL_TXDMA
#ifdef USE_DMA0
  dma_config(0);
  dma_attach(0);
#endif
#ifdef USE_DMA1
  dma_config(1);
  dma_attach(1);
#endif
#endif
}

/****************************************************************************
 * Name: up_putc
 *
 * Description:
 *   Provide priority, low-level access to support OS debug writes
 *
 ****************************************************************************/

void up_putc(int ch)
{
#ifdef HAVE_SERIAL_CONSOLE
  uint32_t intena;

  esp32_disableallints(CONSOLE_DEV.priv, &intena);

  while (!esp32_txready(&CONSOLE_DEV));
  esp32_send(&CONSOLE_DEV, ch);

  esp32_restoreuartint(CONSOLE_DEV.priv, intena);
#endif
}
#endif /* USE_SERIALDRIVER */