Kernel STDIO

STDIN works in a following loop:

• when _kernel_stdio() called it sibscribes to EVT_USERCON_KEY event
• kernel shell when entered into never ending loop calls _kernel_getKey() blocking call that in loop polls SIGIO (see kernel_signal.h) flagged up by _kernel_sigwait()

  Note

  _kernel_getKey() calls _kernel_pipeline() which runs services registered via _SERVICE and exectues queued events

• when EVT_USERCON_KEY is published and the subscriber is called by _kernel_pipeline() it sets new input key and raises SIGIO signal to the kernel (see kernel_signal.h):
  • kernel flags up a signal. _kernel_getKey() drops awaited SIGIO and returns a new key input set by an event subscriber called
  • shell reacts on a new key input and places it into the command buffer.

    Note

    when its a return key it treats a command buffer filled with command to be executed.

  • shell at any new ASCII input received forwards to the STDOUT.
  • shell calls _kernel_getKey() again.

Warning

SIGIO reserved for STDIN usage only any attempt to raise it by the target logic shall result the shell recognizing a new key input as such since a key is unknown (or retain previous state) the behaviour is undefined when the shell will start processing a 'new' input. It doesnt apply to EVT_USERCON_KEY event publish i.e. it can be published anywhere anytime during system lifetime

STDOUT logic just outputs characters to the console (see kernel_stdio.h and console.h).

That said anything that publishes EVT_USERCON_KEY event the kernel shell treats it as a new user input.

Note

it doesnt care what is the exact source and how many of them are e.g. tty/keyb/network etc.

As such the most sutable place publishing events are services registered by _SERVICE

STDIN target platform service example

#include <stdbool.h>
 
#include "uart.h"
#include "events.h"
 
#include "kernel.h"
#include "service.h"
 
static void uart_service(void);
static inline bool is_charValid(char c);
 
_SERVICE(uart_svc, uart_service);
 
static void uart_service(void) {
 
    char c;
    while((c = _uart_read()) != '\0') {
 
        if (is_charValid(c)) {
 
            console_key_t key = { .code = c, .scan_code = 0 };
            _kernel_pubEvt(EVT_USERCON_KEY, (evt_data_t *) &key);
        }
    }
}
 
static inline bool is_charValid(char c) {
 
   return ((c >= '0') && (c <= '9')) || 
               ((c >= 'a') && (c <= 'z')) ||
               ((c >= 'A') && (c <= 'Z')) ||
               ((c == ' ') || (c == '\n') || (c == '\t') || (c == '\b') || (c == '\x7f'));
}