Console

The console is an operating system window where users interact with the OS subsystems or a console application. A user typically inputs text from a keyboard and reads the OS output text on a computer monitor. The text is sent as a sequence of characters between the user and the OS.

You can configure the console to communicate via a UART or the SEGGER Real Time Terminal (RTT) . The CONSOLE_UART syscfg setting enables the communication via a UART and is enabled by default. The CONSOLE_RTT setting enables the communication via the RTT and is disabled by default. When the CONSOLE_UART setting is enabled, the following settings apply:

  • CONSOLE_UART_DEV: Specifies the UART device to use. The default is uart0.
  • CONSOLE_UART_BAUD: Specifies the UART baud rate. The default is 115200.
  • CONSOLE_UART_FLOW_CONTROL: Specifies the UART flow control. The default is UART_FLOW_CONTROL_NONE.
  • CONSOLE_UART_TX_BUF_SIZE: Specifies the transmit buffer size and must be a power of 2. The default is 32.

The CONSOLE_TICKS setting enables the console to print the current OS ticks in each output line.

Notes:

  • SEGGER RTT support is not available in the Mynewt 1.0 console package.
  • The console package is initialized during system initialization (sysinit) so you do not need to initialize the console. However, if you use the Mynewt 1.0 console API to read from the console, you will need to call the console_init() function to enable backward compatibility support.

Description

In the Mynewt OS, the console library comes in three versions:

  • The sys/console/full package implements the complete console functionality and API.
  • The sys/console/stub package implements stubs for the API.
  • The sys/console/minimal package implements minimal console functionality of reading from and writing to console. It implements the console_read() and console_write() functions and stubs for all the other console functions.

All the packages export the console API, and any package that uses the console API must list console as a requirement its pkg.yml file:

pkg.name: sys/shell
pkg.deps:
    - kernel/os
    - encoding/base64
    - time/datetime
    - util/crc
pkg.req_apis:
    - console


The project pkg.yml file also specifies the version of the console package to use.


Using the Full Console Package

A project that requires the full console capability must list the sys/console/full package as a dependency in its pkg.yml file.

An example is the slinky application. It requires the full console capability and has the following pkg.yml file:

pkg.name: apps/slinky
pkg.deps:
    - test/flash_test
    - mgmt/imgmgr
    - mgmt/newtmgr
    - mgmt/newtmgr/transport/nmgr_shell
    - kernel/os
    - boot/bootutil
    - sys/shell
    - sys/console/full
       ...
    - sys/id


Using the Stub Console Package

A project that uses console stub API must list the sys/console/stub package as a dependency in its pkg.yml file.

Examples of when a project would use the console stubs might be:

  • A project may not have a physical console (e.g. a UART port to connect a terminal to) but may have a dependency on a package that has console capability.
  • A bootloader project where we want to keep the size of the image small. It includes the kernel/os package that can print out messages on a console (e.g. if there is a hard fault). However, we do not want to use any console I/O capability in this particular bootloader project to keep the size small.

The project would use the console stub API and has the following pkg.yml file:

Another example would be the bootloader project where we want to keep the size of the image small. It includes the libs/os pkg that can print out messages on a console (e.g. if there is a hard fault) and the libs/util pkg that uses full console (but only if SHELL is present to provide a CLI). However, we do not want to use any console I/O capability in this particular bootloader project to keep the size small. We simply use the console stub instead, and the pkg.yml file for the project boot pkg looks like the following:

pkg.name: apps/boot
pkg.deps:
    - boot/bootutil
    - kernel/os
    - sys/console/stub


Using the Minimal Console Package

There might be projects that need to read and write data on a serial connection but do not need the full console capability. An example might be a project that supports serial image upgrade but does not need full newtmgr capability. The project would use the console minimal API and has the following pkg.yml file:

pkg.name: apps/boot
pkg.type: app
pkg.description: Boot loader application.
pkg.author: "Apache Mynewt <dev@mynewt.apache.org>"
pkg.homepage: "http://mynewt.apache.org/"
pkg.keywords:
    - loader

pkg.deps:
    - boot/bootutil
    - kernel/os
    - sys/console/stub

pkg.deps.BOOT_SERIAL.OVERWRITE:
    - sys/console/minimal
    - boot/boot_serial


Output to the Console

You use the console_write() function to write raw output and the console_printf() function to write a C-style formatted string to the console.


Input from the Console

The following syscfg settings control input from the console:

  • CONSOLE_INPUT: Enables input from the console. The setting is enabled by default.
  • CONSOLE_ECHO: Enables echoing of the received data back to the console. Echoing is enabled by default. Terminal programs expect this, and is a way for the user to know that the console is connected and responsive. You can also use the console_echo() function to set echo on or off programatically.
  • CONSOLE_MAX_INPUT_LEN: Specifies the maximum input line length.


The Mynewt 1.1 console package adds a new API for reading input data from the console. The package supports backward compatibility for the Mynewt 1.0 console API. The steps you use to receive data from the console for each API version are provided below.


Mynewt 1.0 Console API

To use the Mynewt 1.0 console API for reading input from the console, you perform the follow steps:

  1. Call the console_init() function and pass either a pointer to a callback function or NULL for the argument. The console calls this callback function, if specified, when it receives a full line of data.

  2. Call the console_read() function to read the input data.

Note: The CONSOLE_COMPAT syscfg setting must be set to 1 to enable backward compatibility support. The setting is enabled by default.


Mynewt 1.1 Console API

Mynewt 1.1 console API adds the console_set_queues(struct os_eventq *avail_queue, struct os_eventq *lines_queue) function. An application or the package, such as the shell, calls this function to specify two event queues that the console uses to manage input data buffering and to send notification when a full line of data is received. The two event queues are used as follows:

  • avail_queue: Each event in this queue indicates that a buffer is available for the console to use for buffering input data.

    The caller must initialize the avail_queue and initialize and add an os_event to the avail_queue before calling the console_set_queues() function. The fields for the event should be set as follows:

    • ev_cb: Pointer to the callback function to call when a full line of data is received.
    • ev_arg: Pointer to a console_input structure. This structure contains a data buffer to store the current input.

    The console removes an event from this queue and uses the console_input buffer from this event to buffer the received characters until it receives a new line, '/n', character. When the console receives a full line of data, it adds this event to the lines_queue.

  • lines_queue: Each event in this queue indicates a full line of data is received and ready for processing. The console adds an event to this queue when it receives a full line of data. This event is the same event that the console removes from the avail_queue.

    The task that manages the lines_queue removes an event from the queue and calls the event callback function to process the input line. The event callback function must add the event back to the avail_queue when it completes processing the current input data, and allows the console to use the console_input buffer set for this event to buffer input data.

    We recommend that you use the OS default queue for the lines_queue so that the callback is processed in the context of the OS main task. If you do not use the OS default event queue, you must initialize an event queue and create a task to process events from the queue.

    Note: If the callback function needs to read another line of input from the console while processing the current line, it may use the console_read() function to read the next line of input from the console. The console will need another console_input buffer to store the next input line, so two events, initialized with the pointers to the callback and the console_input buffer, must be added to the avail_queue.


Here is a code excerpt that shows how to use the console_set_queues() function. The example adds one event to the avail_queue and uses the OS default event queue for the lines_queue.

static void myapp_process_input(struct os_event *ev);

static struct os_eventq avail_queue;

static struct console_input myapp_console_buf;

static struct os_event myapp_console_event = {
    .ev_cb = myapp_process_input,
    .ev_arg = &myapp_console_buf
};

/* Event callback to process a line of input from console. */
static void
myapp_process_input(struct os_event *ev)
{
    char *line;
    struct console_input *input;

    input = ev->ev_arg;
    assert (input != NULL);

    line = input->line;
    /* Do some work with line */
         ....
    /* Done processing line. Add the event back to the avail_queue */
    os_eventq_put(&avail_queue, ev);
    return;
}

static void 
myapp_init(void)
{
    os_eventq_init(&avail_queue);
    os_eventq_put(&avail_queue, &myapp_console_event);

    console_set_queues(&avail_queue, os_eventq_dflt_get());
}


Data structures

The struct console_input data structure represents a console input buffer. Each event added to the console avail_queue must have the ev_arg field point to a console_input structure.

struct console_input {
    char line[MYNEWT_VAL(CONSOLE_MAX_INPUT_LEN)];
};
Element Description
line Data buffer that the console uses to save received characters until a new line is received.

List of Functions

The functions available in console are:

Function Description
console_echo Controls whether echoing is on or off for the console.
console_init (Mynewt 1.0 API) Initializes the console.
console_is_init Returns a value indicating whether the console has been initialized or not.
console_printf Writes a formatted message instead of raw output to the console.
console_read Copies up the to given number of bytes to the input string.
console_set_queues Specifies the event queues for the console to use to manage input data.
console_write Queues characters to console display over serial port.