Introduction

OS startup behaviour

When MiraOS starts up, it will automatically call the function mira_setup() which is the application's entry point. From here peripherals can be initialised, processes started, etc.

Note: processes started from mira_setup must pause once with a call to PROCESS_PAUSE() immediately after PROCESS_BEGIN() to let the kernel finalise initialisation before executing the process.

Input/output

MiraOS can use file descriptors to use with dprintf. These can be listed in the MIRA_IODEFS list. The three first are the standard file descriptors stdin, stdout and stderr.

MIRA_IODEFS(
    MIRA_IODEF_NONE,    /* fd 0: stdin */
    MIRA_IODEF_NONE,    /* fd 1: stdout */
    MIRA_IODEF_NONE     /* fd 2: stderr */
);

These can be mapped towards input/output routines, for instance write/read functions for a UART.

Example

To be able to have printf() sending it's output to a serial terminal on a PC, we would need to map stdout to UART0 and connect UART0 to the PC's serial port.

UART0 needs to be properly initialised for this to work.

MIRA_IODEFS(
    MIRA_IODEF_NONE,    /* fd 0: stdin */
    MIRA_IODEF_UART(0), /* fd 1: stdout */
    MIRA_IODEF_NONE     /* fd 2: stderr */
);

Minimal MiraOS application

The following application is the minimal MiraOS application that can be written. It can be used as a starting point for your applications.

#include <mira.h>

MIRA_IODEFS(
    MIRA_IODEF_NONE,    /* fd 0: stdin */
    MIRA_IODEF_NONE,    /* fd 1: stdout */
    MIRA_IODEF_NONE     /* fd 2: stderr */
);

PROCESS(main_proc, "Main process");

void mira_setup(void)
{
    process_start(&main_proc, NULL);
}

PROCESS_THREAD(main_proc, ev, data)
{
    PROCESS_BEGIN();
    /* Pause once, so we don't run anything before finish of startup */
    PROCESS_PAUSE();

    /* Here's the place for the process' code */

    PROCESS_END();
}