esp-idf/components/vfs/vfs_uart.c

// Copyright 2015-2017 Espressif Systems (Shanghai) PTE LTD
//
// 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 <string.h>
#include <stdbool.h>
#include <stdarg.h>
#include <sys/errno.h>
#include <sys/lock.h>
#include <sys/fcntl.h>
#include <sys/param.h>
#include "esp_vfs.h"
#include "esp_vfs_dev.h"
#include "esp_attr.h"
#include "soc/uart_struct.h"
#include "driver/uart.h"
#include "sdkconfig.h"
#include "driver/uart_select.h"
#include "rom/uart.h"

// TODO: make the number of UARTs chip dependent
#define UART_NUM 3

// Token signifying that no character is available
#define NONE -1

// UART write bytes function type
typedef void (*tx_func_t)(int, int);
// UART read bytes function type
typedef int (*rx_func_t)(int);

// Basic functions for sending and receiving bytes over UART
static void uart_tx_char(int fd, int c);
static int uart_rx_char(int fd);

// Functions for sending and receiving bytes which use UART driver
static void uart_tx_char_via_driver(int fd, int c);
static int uart_rx_char_via_driver(int fd);

// Pointers to UART peripherals
static uart_dev_t* s_uarts[UART_NUM] = {&UART0, &UART1, &UART2};
// per-UART locks, lazily initialized
static _lock_t s_uart_read_locks[UART_NUM];
static _lock_t s_uart_write_locks[UART_NUM];
// One-character buffer used for newline conversion code, per UART
static int s_peek_char[UART_NUM] = { NONE, NONE, NONE };
// Per-UART non-blocking flag. Note: default implementation does not honor this
// flag, all reads are non-blocking. This option becomes effective if UART
// driver is used.
static bool s_non_blocking[UART_NUM];

/* Lock ensuring that uart_select is used from only one task at the time */
static _lock_t s_one_select_lock;

static SemaphoreHandle_t *_signal_sem = NULL;
static fd_set *_readfds = NULL;
static fd_set *_writefds = NULL;
static fd_set *_errorfds = NULL;
static fd_set *_readfds_orig = NULL;
static fd_set *_writefds_orig = NULL;
static fd_set *_errorfds_orig = NULL;

// Newline conversion mode when transmitting
static esp_line_endings_t s_tx_mode =
#if CONFIG_NEWLIB_STDOUT_LINE_ENDING_CRLF
        ESP_LINE_ENDINGS_CRLF;
#elif CONFIG_NEWLIB_STDOUT_LINE_ENDING_CR
        ESP_LINE_ENDINGS_CR;
#else
        ESP_LINE_ENDINGS_LF;
#endif

// Newline conversion mode when receiving
static esp_line_endings_t s_rx_mode[UART_NUM] = { [0 ... UART_NUM-1] =
#if CONFIG_NEWLIB_STDIN_LINE_ENDING_CRLF
        ESP_LINE_ENDINGS_CRLF
#elif CONFIG_NEWLIB_STDIN_LINE_ENDING_CR
        ESP_LINE_ENDINGS_CR
#else
        ESP_LINE_ENDINGS_LF
#endif
};

static void uart_end_select();

// Functions used to write bytes to UART. Default to "basic" functions.
static tx_func_t s_uart_tx_func[UART_NUM] = {
        &uart_tx_char, &uart_tx_char, &uart_tx_char
};

// Functions used to read bytes from UART. Default to "basic" functions.
static rx_func_t s_uart_rx_func[UART_NUM] = {
        &uart_rx_char, &uart_rx_char, &uart_rx_char
};


static int uart_open(const char * path, int flags, int mode)
{
    // this is fairly primitive, we should check if file is opened read only,
    // and error out if write is requested
    int fd = -1;

    if (strcmp(path, "/0") == 0) {
        fd = 0;
    } else if (strcmp(path, "/1") == 0) {
        fd = 1;
    } else if (strcmp(path, "/2") == 0) {
        fd = 2;
    } else {
        errno = ENOENT;
        return fd;
    }

    s_non_blocking[fd] = ((flags & O_NONBLOCK) == O_NONBLOCK);

    return fd;
}

static void uart_tx_char(int fd, int c)
{
    uart_dev_t* uart = s_uarts[fd];
    while (uart->status.txfifo_cnt >= 127) {
        ;
    }
    uart->fifo.rw_byte = c;
}

static void uart_tx_char_via_driver(int fd, int c)
{
    char ch = (char) c;
    uart_write_bytes(fd, &ch, 1);
}

static int uart_rx_char(int fd)
{
    uart_dev_t* uart = s_uarts[fd];
    if (uart->status.rxfifo_cnt == 0) {
        return NONE;
    }
    return uart->fifo.rw_byte;
}

static int uart_rx_char_via_driver(int fd)
{
    uint8_t c;
    int timeout = s_non_blocking[fd] ? 0 : portMAX_DELAY;
    int n = uart_read_bytes(fd, &c, 1, timeout);
    if (n <= 0) {
        return NONE;
    }
    return c;
}

static ssize_t uart_write(int fd, const void * data, size_t size)
{
    assert(fd >=0 && fd < 3);
    const char *data_c = (const char *)data;
    /*  Even though newlib does stream locking on each individual stream, we need
     *  a dedicated UART lock if two streams (stdout and stderr) point to the
     *  same UART.
     */
    _lock_acquire_recursive(&s_uart_write_locks[fd]);
    for (size_t i = 0; i < size; i++) {
        int c = data_c[i];
        if (c == '\n' && s_tx_mode != ESP_LINE_ENDINGS_LF) {
            s_uart_tx_func[fd](fd, '\r');
            if (s_tx_mode == ESP_LINE_ENDINGS_CR) {
                continue;
            }
        }
        s_uart_tx_func[fd](fd, c);
    }
    _lock_release_recursive(&s_uart_write_locks[fd]);
    return size;
}

/* Helper function which returns a previous character or reads a new one from
 * UART. Previous character can be returned ("pushed back") using
 * uart_return_char function.
 */
static int uart_read_char(int fd)
{
    /* return character from peek buffer, if it is there */
    if (s_peek_char[fd] != NONE) {
        int c = s_peek_char[fd];
        s_peek_char[fd] = NONE;
        return c;
    }
    return s_uart_rx_func[fd](fd);
}

/* Push back a character; it will be returned by next call to uart_read_char */
static void uart_return_char(int fd, int c)
{
    assert(s_peek_char[fd] == NONE);
    s_peek_char[fd] = c;
}

static ssize_t uart_read(int fd, void* data, size_t size)
{
    assert(fd >=0 && fd < 3);
    char *data_c = (char *) data;
    size_t received = 0;
    _lock_acquire_recursive(&s_uart_read_locks[fd]);
    while (received < size) {
        int c = uart_read_char(fd);
        if (c == '\r') {
            if (s_rx_mode[fd] == ESP_LINE_ENDINGS_CR) {
                c = '\n';
            } else if (s_rx_mode[fd] == ESP_LINE_ENDINGS_CRLF) {
                /* look ahead */
                int c2 = uart_read_char(fd);
                if (c2 == NONE) {
                    /* could not look ahead, put the current character back */
                    uart_return_char(fd, c);
                    break;
                }
                if (c2 == '\n') {
                    /* this was \r\n sequence. discard \r, return \n */
                    c = '\n';
                } else {
                    /* \r followed by something else. put the second char back,
                     * it will be processed on next iteration. return \r now.
                     */
                    uart_return_char(fd, c2);
                }
            }
        } else if (c == NONE) {
            break;
        }
        data_c[received] = (char) c;
        ++received;
        if (c == '\n') {
            break;
        }
    }
    _lock_release_recursive(&s_uart_read_locks[fd]);
    if (received > 0) {
        return received;
    }
    errno = EWOULDBLOCK;
    return -1;
}

static int uart_fstat(int fd, struct stat * st)
{
    assert(fd >=0 && fd < 3);
    st->st_mode = S_IFCHR;
    return 0;
}

static int uart_close(int fd)
{
    assert(fd >=0 && fd < 3);
    return 0;
}

static int uart_fcntl(int fd, int cmd, va_list args)
{
    assert(fd >=0 && fd < 3);
    int result = 0;
    if (cmd == F_GETFL) {
        if (s_non_blocking[fd]) {
            result |= O_NONBLOCK;
        }
    } else if (cmd == F_SETFL) {
        int arg = va_arg(args, int);
        s_non_blocking[fd] = (arg & O_NONBLOCK) != 0;
    } else {
        // unsupported operation
        result = -1;
        errno = ENOSYS;
    }
    return result;
}

static int uart_access(const char *path, int amode)
{
    int ret = -1;

    if (strcmp(path, "/0") == 0 || strcmp(path, "/1") == 0 || strcmp(path, "/2") == 0) {
        if (F_OK == amode) {
            ret = 0; //path exists
        } else {
            if ((((amode & R_OK) == R_OK) || ((amode & W_OK) == W_OK)) && ((amode & X_OK) != X_OK)) {
                ret = 0; //path is readable and/or writable but not executable
            } else {
                errno = EACCES;
            }
        }
    } else {
        errno = ENOENT;
    }

    return ret;
}

static int uart_fsync(int fd)
{
    assert(fd >= 0 && fd < 3);
    _lock_acquire_recursive(&s_uart_write_locks[fd]);
    uart_tx_wait_idle((uint8_t) fd);
    _lock_release_recursive(&s_uart_write_locks[fd]);
    return 0;
}

static void select_notif_callback(uart_port_t uart_num, uart_select_notif_t uart_select_notif, BaseType_t *task_woken)
{
    switch (uart_select_notif) {
        case UART_SELECT_READ_NOTIF:
            if (FD_ISSET(uart_num, _readfds_orig)) {
                FD_SET(uart_num, _readfds);
                esp_vfs_select_triggered_isr(_signal_sem, task_woken);
            }
            break;
        case UART_SELECT_WRITE_NOTIF:
            if (FD_ISSET(uart_num, _writefds_orig)) {
                FD_SET(uart_num, _writefds);
                esp_vfs_select_triggered_isr(_signal_sem, task_woken);
            }
            break;
        case UART_SELECT_ERROR_NOTIF:
            if (FD_ISSET(uart_num, _errorfds_orig)) {
                FD_SET(uart_num, _errorfds);
                esp_vfs_select_triggered_isr(_signal_sem, task_woken);
            }
            break;
    }
}

static esp_err_t uart_start_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, SemaphoreHandle_t *signal_sem)
{
    if (_lock_try_acquire(&s_one_select_lock)) {
        return ESP_ERR_INVALID_STATE;
    }

    const int max_fds = MIN(nfds, UART_NUM);

    portENTER_CRITICAL(uart_get_selectlock());

    if (_readfds || _writefds || _errorfds || _readfds_orig || _writefds_orig || _errorfds_orig || _signal_sem) {
        portEXIT_CRITICAL(uart_get_selectlock());
        uart_end_select();
        return ESP_ERR_INVALID_STATE;
    }

    if ((_readfds_orig = malloc(sizeof(fd_set))) == NULL) {
        portEXIT_CRITICAL(uart_get_selectlock());
        uart_end_select();
        return ESP_ERR_NO_MEM;
    }

    if ((_writefds_orig = malloc(sizeof(fd_set))) == NULL) {
        portEXIT_CRITICAL(uart_get_selectlock());
        uart_end_select();
        return ESP_ERR_NO_MEM;
    }

    if ((_errorfds_orig = malloc(sizeof(fd_set))) == NULL) {
        portEXIT_CRITICAL(uart_get_selectlock());
        uart_end_select();
        return ESP_ERR_NO_MEM;
    }

    //uart_set_select_notif_callback set the callbacks in UART ISR
    for (int i = 0; i < max_fds; ++i) {
        if (FD_ISSET(i, readfds) || FD_ISSET(i, writefds) || FD_ISSET(i, exceptfds)) {
            uart_set_select_notif_callback(i, select_notif_callback);
        }
    }

    _signal_sem = signal_sem;

    _readfds = readfds;
    _writefds = writefds;
    _errorfds = exceptfds;

    *_readfds_orig = *readfds;
    *_writefds_orig = *writefds;
    *_errorfds_orig = *exceptfds;

    FD_ZERO(readfds);
    FD_ZERO(writefds);
    FD_ZERO(exceptfds);

    for (int i = 0; i < max_fds; ++i) {
        if (FD_ISSET(i, _readfds_orig)) {
            size_t buffered_size;
            if (uart_get_buffered_data_len(i, &buffered_size) == ESP_OK && buffered_size > 0) {
                // signalize immediately when data is buffered
                FD_SET(i, _readfds);
                esp_vfs_select_triggered(_signal_sem);
            }
        }
    }

    portEXIT_CRITICAL(uart_get_selectlock());
    // s_one_select_lock is not released on successfull exit - will be
    // released in uart_end_select()

    return ESP_OK;
}

static void uart_end_select()
{
    portENTER_CRITICAL(uart_get_selectlock());
    for (int i = 0; i < UART_NUM; ++i) {
        uart_set_select_notif_callback(i, NULL);
    }

    _signal_sem = NULL;

    _readfds = NULL;
    _writefds = NULL;
    _errorfds = NULL;

    if (_readfds_orig) {
        free(_readfds_orig);
        _readfds_orig = NULL;
    }

    if (_writefds_orig) {
        free(_writefds_orig);
        _writefds_orig = NULL;
    }

    if (_errorfds_orig) {
        free(_errorfds_orig);
        _errorfds_orig = NULL;
    }
    portEXIT_CRITICAL(uart_get_selectlock());
    _lock_release(&s_one_select_lock);
}

#ifdef CONFIG_SUPPORT_TERMIOS
static int uart_tcsetattr(int fd, int optional_actions, const struct termios *p)
{
    if (fd < 0 || fd >= UART_NUM) {
        errno = EBADF;
        return -1;
    }

    if (p == NULL) {
        errno = EINVAL;
        return -1;
    }

    switch (optional_actions) {
        case TCSANOW:
            // nothing to do
            break;
        case TCSADRAIN:
            if (uart_wait_tx_done(fd, portMAX_DELAY) != ESP_OK) {
                errno = EINVAL;
                return -1;
            }

            /* FALLTHRU */

        case TCSAFLUSH:
            if (uart_flush_input(fd) != ESP_OK) {
                errno = EINVAL;
                return -1;
            }
            break;
        default:
            errno = EINVAL;
            return -1;
    }

    if (p->c_iflag & IGNCR) {
        s_rx_mode[fd] = ESP_LINE_ENDINGS_CRLF;
    } else if (p->c_iflag & ICRNL) {
        s_rx_mode[fd] = ESP_LINE_ENDINGS_CR;
    } else {
        s_rx_mode[fd] = ESP_LINE_ENDINGS_LF;
    }

    // output line endings are not supported because there is no alternative in termios for converting LF to CR

    {
        uart_word_length_t data_bits;
        const tcflag_t csize_bits = p->c_cflag & CSIZE;

        switch (csize_bits) {
            case CS5:
                data_bits = UART_DATA_5_BITS;
                break;
            case CS6:
                data_bits = UART_DATA_6_BITS;
                break;
            case CS7:
                data_bits = UART_DATA_7_BITS;
                break;
            case CS8:
                data_bits = UART_DATA_8_BITS;
                break;
            default:
                errno = EINVAL;
                return -1;
        }

        if (uart_set_word_length(fd, data_bits) != ESP_OK) {
            errno = EINVAL;
            return -1;
        }
    }

    if (uart_set_stop_bits(fd, (p->c_cflag & CSTOPB) ? UART_STOP_BITS_2 : UART_STOP_BITS_1) != ESP_OK) {
        errno = EINVAL;
        return -1;
    }

    if (uart_set_parity(fd, (p->c_cflag & PARENB) ?
                ((p->c_cflag & PARODD) ? UART_PARITY_ODD : UART_PARITY_EVEN)
                :
                UART_PARITY_DISABLE) != ESP_OK) {
        errno = EINVAL;
        return -1;
    }

    if (p->c_cflag & (CBAUD | CBAUDEX)) {
        if (p->c_ispeed != p->c_ospeed) {
            errno = EINVAL;
            return -1;
        } else {
            uint32_t b;
            if (p->c_cflag & BOTHER) {
                b = p->c_ispeed;
            } else {
                switch (p->c_ispeed) {
                    case B0:
                        b = 0;
                        break;
                    case B50:
                        b = 50;
                        break;
                    case B75:
                        b = 75;
                        break;
                    case B110:
                        b = 110;
                        break;
                    case B134:
                        b = 134;
                        break;
                    case B150:
                        b = 150;
                        break;
                    case B200:
                        b = 200;
                        break;
                    case B300:
                        b = 300;
                        break;
                    case B600:
                        b = 600;
                        break;
                    case B1200:
                        b = 1200;
                        break;
                    case B1800:
                        b = 1800;
                        break;
                    case B2400:
                        b = 2400;
                        break;
                    case B4800:
                        b = 4800;
                        break;
                    case B9600:
                        b = 9600;
                        break;
                    case B19200:
                        b = 19200;
                        break;
                    case B38400:
                        b = 38400;
                        break;
                    case B57600:
                        b = 57600;
                        break;
                    case B115200:
                        b = 115200;
                        break;
                    case B230400:
                        b = 230400;
                        break;
                    case B460800:
                        b = 460800;
                        break;
                    case B500000:
                        b = 500000;
                        break;
                    case B576000:
                        b = 576000;
                        break;
                    case B921600:
                        b = 921600;
                        break;
                    case B1000000:
                        b = 1000000;
                        break;
                    case B1152000:
                        b = 1152000;
                        break;
                    case B1500000:
                        b = 1500000;
                        break;
                    case B2000000:
                        b = 2000000;
                        break;
                    case B2500000:
                        b = 2500000;
                        break;
                    case B3000000:
                        b = 3000000;
                        break;
                    case B3500000:
                        b = 3500000;
                        break;
                    case B4000000:
                        b = 4000000;
                        break;
                    default:
                        errno = EINVAL;
                        return -1;
                }
            }

            if (uart_set_baudrate(fd, b) != ESP_OK) {
                errno = EINVAL;
                return -1;
            }
        }
    }

    return 0;
}

static int uart_tcgetattr(int fd, struct termios *p)
{
    if (fd < 0 || fd >= UART_NUM) {
        errno = EBADF;
        return -1;
    }

    if (p == NULL) {
        errno = EINVAL;
        return -1;
    }

    memset(p, 0, sizeof(struct termios));

    if (s_rx_mode[fd] == ESP_LINE_ENDINGS_CRLF) {
        p->c_iflag |= IGNCR;
    } else if (s_rx_mode[fd] == ESP_LINE_ENDINGS_CR) {
        p->c_iflag |= ICRNL;
    }

    {
        uart_word_length_t data_bits;

        if (uart_get_word_length(fd, &data_bits) != ESP_OK) {
            errno = EINVAL;
            return -1;
        }

        p->c_cflag &= (~CSIZE);

        switch (data_bits) {
            case UART_DATA_5_BITS:
                p->c_cflag |= CS5;
                break;
            case UART_DATA_6_BITS:
                p->c_cflag |= CS6;
                break;
            case UART_DATA_7_BITS:
                p->c_cflag |= CS7;
                break;
            case UART_DATA_8_BITS:
                p->c_cflag |= CS8;
                break;
            default:
                errno = ENOSYS;
                return -1;
        }
    }

    {
        uart_stop_bits_t stop_bits;
        if (uart_get_stop_bits(fd, &stop_bits) != ESP_OK) {
            errno = EINVAL;
            return -1;
        }

        switch (stop_bits) {
            case UART_STOP_BITS_1:
                // nothing to do
                break;
            case UART_STOP_BITS_2:
                p->c_cflag |= CSTOPB;
                break;
            default:
                // UART_STOP_BITS_1_5 is unsupported by termios
                errno = ENOSYS;
                return -1;
        }
    }

    {
        uart_parity_t parity_mode;
        if (uart_get_parity(fd, &parity_mode) != ESP_OK) {
            errno = EINVAL;
            return -1;
        }

        switch (parity_mode) {
            case UART_PARITY_EVEN:
                p->c_cflag |= PARENB;
                break;
            case UART_PARITY_ODD:
                p->c_cflag |= (PARENB | PARODD);
                break;
            case UART_PARITY_DISABLE:
                // nothing to do
                break;
            default:
                errno = ENOSYS;
                return -1;
        }
    }

    {
        uint32_t baudrate;
        if (uart_get_baudrate(fd, &baudrate) != ESP_OK) {
            errno = EINVAL;
            return -1;
        }

        p->c_cflag |= (CBAUD | CBAUDEX);

        speed_t sp;
        switch (baudrate) {
            case 0:
                sp = B0;
                break;
            case 50:
                sp = B50;
                break;
            case 75:
                sp = B75;
                break;
            case 110:
                sp = B110;
                break;
            case 134:
                sp = B134;
                break;
            case 150:
                sp = B150;
                break;
            case 200:
                sp = B200;
                break;
            case 300:
                sp = B300;
                break;
            case 600:
                sp = B600;
                break;
            case 1200:
                sp = B1200;
                break;
            case 1800:
                sp = B1800;
                break;
            case 2400:
                sp = B2400;
                break;
            case 4800:
                sp = B4800;
                break;
            case 9600:
                sp = B9600;
                break;
            case 19200:
                sp = B19200;
                break;
            case 38400:
                sp = B38400;
                break;
            case 57600:
                sp = B57600;
                break;
            case 115200:
                sp = B115200;
                break;
            case 230400:
                sp = B230400;
                break;
            case 460800:
                sp = B460800;
                break;
            case 500000:
                sp = B500000;
                break;
            case 576000:
                sp = B576000;
                break;
            case 921600:
                sp = B921600;
                break;
            case 1000000:
                sp = B1000000;
                break;
            case 1152000:
                sp = B1152000;
                break;
            case 1500000:
                sp = B1500000;
                break;
            case 2000000:
                sp = B2000000;
                break;
            case 2500000:
                sp = B2500000;
                break;
            case 3000000:
                sp = B3000000;
                break;
            case 3500000:
                sp = B3500000;
                break;
            case 4000000:
                sp = B4000000;
                break;
            default:
                p->c_cflag |= BOTHER;
                sp = baudrate;
                break;
        }

        p->c_ispeed = p->c_ospeed = sp;
    }

    return 0;
}

static int uart_tcdrain(int fd)
{
    if (fd < 0 || fd >= UART_NUM) {
        errno = EBADF;
        return -1;
    }

    if (uart_wait_tx_done(fd, portMAX_DELAY) != ESP_OK) {
        errno = EINVAL;
        return -1;
    }

    return 0;
}

static int uart_tcflush(int fd, int select)
{
    if (fd < 0 || fd >= UART_NUM) {
        errno = EBADF;
        return -1;
    }

    if (select == TCIFLUSH) {
        if (uart_flush_input(fd) != ESP_OK) {
            errno = EINVAL;
            return -1;
        }
    } else {
        // output flushing is not supported
        errno = EINVAL;
        return -1;
    }

    return 0;
}
#endif // CONFIG_SUPPORT_TERMIOS

void esp_vfs_dev_uart_register()
{
    esp_vfs_t vfs = {
        .flags = ESP_VFS_FLAG_DEFAULT,
        .write = &uart_write,
        .open = &uart_open,
        .fstat = &uart_fstat,
        .close = &uart_close,
        .read = &uart_read,
        .fcntl = &uart_fcntl,
        .fsync = &uart_fsync,
        .access = &uart_access,
        .start_select = &uart_start_select,
        .end_select = &uart_end_select,
#ifdef CONFIG_SUPPORT_TERMIOS
        .tcsetattr = &uart_tcsetattr,
        .tcgetattr = &uart_tcgetattr,
        .tcdrain = &uart_tcdrain,
        .tcflush = &uart_tcflush,
#endif // CONFIG_SUPPORT_TERMIOS
    };
    ESP_ERROR_CHECK(esp_vfs_register("/dev/uart", &vfs, NULL));
}

void esp_vfs_dev_uart_set_rx_line_endings(esp_line_endings_t mode)
{
    for (int i = 0; i < UART_NUM; ++i) {
        s_rx_mode[i] = mode;
    }
}

void esp_vfs_dev_uart_set_tx_line_endings(esp_line_endings_t mode)
{
    s_tx_mode = mode;
}

void esp_vfs_dev_uart_use_nonblocking(int uart_num)
{
    _lock_acquire_recursive(&s_uart_read_locks[uart_num]);
    _lock_acquire_recursive(&s_uart_write_locks[uart_num]);
    s_uart_tx_func[uart_num] = uart_tx_char;
    s_uart_rx_func[uart_num] = uart_rx_char;
    _lock_release_recursive(&s_uart_write_locks[uart_num]);
    _lock_release_recursive(&s_uart_read_locks[uart_num]);
}

void esp_vfs_dev_uart_use_driver(int uart_num)
{
    _lock_acquire_recursive(&s_uart_read_locks[uart_num]);
    _lock_acquire_recursive(&s_uart_write_locks[uart_num]);
    s_uart_tx_func[uart_num] = uart_tx_char_via_driver;
    s_uart_rx_func[uart_num] = uart_rx_char_via_driver;
    _lock_release_recursive(&s_uart_write_locks[uart_num]);
    _lock_release_recursive(&s_uart_read_locks[uart_num]);
}