/* this is a simple hello world program */
  #include <stdio.h>
  int main(void)
  {
  printf("Hello, eCos world!\n");
  return 0;
}

To compile this or any other program that is not part of the eCos distribution, you can follow the procedures described below. Type this explicit compilation command (assuming your current working directory is also where you built the eCos kernel):

$ TARGET-gcc -g -I<BASE_DIR>/install/include hello.c -L<BASE_DIR>/install/lib -Ttarget.ld -nostdlib

The compilation command above contains some standard GCC options (for example, -g enables debugging), as well as some mention of paths (-I<BASE_DIR>/install/include allows files like cyg/kernel/kapi.h to be found, and -L<BASE_DIR>/install/lib allowsthe linker to find -Ttarget.ld).

The executable program will be called a.out.

	Note
	Some target systems require special options to be passed to gcc to compile correctly for that system. Please examine the Makefile in the examples directory to see if this applies to your target.

You can now run the resulting program using GDB in exactly the same the way you ran the test case before. The procedure will be the same, but this time run TARGET-gdb specifying -nw a.out on the command line:

$ TARGET-gdb -nw a.out

For targets other than the synthetic linux target, you should now run the usual GDB commands described earlier. Once this is done, typing the command "continue" at the (gdb) prompt ("run" for simulators) will allow the program to execute and print the string "Hello, eCos world!" on your screen.

On the synthetic linux target, you may use the "run" command immediately - you do not need to connect to the target, nor use the "load" command.

#include <cyg/kernel/kapi.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

/* now declare (and allocate space for) some kernel objects,
  like the two threads we will use */
cyg_thread thread_s[2];	/* space for two thread objects */

char stack[2][4096];	/* space for two 4K stacks */

/* now the handles for the threads */
cyg_handle_t simple_threadA, simple_threadB;

/* and now variables for the procedure which is the thread */
cyg_thread_entry_t simple_program;

/* and now a mutex to protect calls to the C library */
cyg_mutex_t cliblock;

/* we install our own startup routine which sets up threads */
void cyg_user_start(void)
{
  printf("Entering twothreads' cyg_user_start() function\n");

  cyg_mutex_init(&cliblock);

  cyg_thread_create(4, simple_program, (cyg_addrword_t) 0,
  "Thread A", (void *) stack[0], 4096,
  &simple_threadA, &thread_s[0]);
  cyg_thread_create(4, simple_program, (cyg_addrword_t) 1,
  "Thread B", (void *) stack[1], 4096,
  &simple_threadB, &thread_s[1]);

  cyg_thread_resume(simple_threadA);
  cyg_thread_resume(simple_threadB);
}

/* this is a simple program which runs in a thread */
void simple_program(cyg_addrword_t data)
{
  int message = (int) data;
  int delay;

  printf("Beginning execution; thread data is %d\n", message);

  cyg_thread_delay(200);

  for (;;) {
    delay = 200 + (rand() % 50);

    /* note: printf() must be protected by a call to cyg_mutex_lock() */
    cyg_mutex_lock(&cliblock);
    printf("Thread %d: and now a delay of %d clock ticks\n", message, delay);
    cyg_mutex_unlock(&cliblock);
    cyg_thread_delay(delay);
  }
}

When you run the program (by typing continue at the (gdb) prompt) the output should look like this:

Starting program: <BASE_DIR>/examples/twothreads.exe
Entering twothreads' cyg_user_start()
function
Beginning execution; thread data is 0
Beginning execution; thread data is 1
Thread 0: and now a delay of 240 clock ticks
Thread 1: and now a delay of 225 clock ticks
Thread 1: and now a delay of 234 clock ticks
Thread 0: and now a delay of 231 clock ticks
Thread 1: and now a delay of 224 clock ticks
Thread 0: and now a delay of 249 clock ticks
Thread 1: and now a delay of 202 clock ticks
Thread 0: and now a delay of 235 clock ticks

	Note
	When running in a simulator the delays might be quite long. On a hardware board (where the clock speed is 100 ticks/second) the delays should average to about 2.25 seconds. In simulation, the delay will depend on the speed of the host processor and will almost always be much slower than the actual board. You might want to reduce the delay parameter when running in simulation.

Figure 9.1, “Two threads with simple print statements after random delays” shows how this multitasking program executes. Note that apart from the thread creation system calls, this program also creates and uses a mutex for synchronization between the printf() calls in the two threads. This is because the C library standard I/O (by default) is configured not to be thread-safe, which means that if more than one thread is using standard I/O they might corrupt each other. This is fixed by a mutual exclusion (or mutex) lockout mechanism: the threads do not call printf() until cyg_mutex_lock() has returned, which only happens when the other thread calls cyg_mutex_unlock().

You could avoid using the mutex by configuring the C library to be thread-safe (by selecting the component CYGSEM_LIBC_STDIO_THREAD_SAFE_STREAMS).

Figure 9.1. Two threads with simple print statements after random delays