This chapter contains a description of the demonstration system that is delivered with all ThreadX processor support packages.

Overview

Each ThreadX product distribution contains a demonstration system that runs on all supported microprocessors.

This example system is defined in the distribution file demo_threadx.c and is designed to illustrate how ThreadX is used in an embedded multithread environment. The demonstration consists of initialization, eight threads, one byte pool, one block pool, one queue, one semaphore, one mutex, and one event flags group.

Note
 Except for the thread’s stack size, the demonstration application is identical on all ThreadX supported processors.

The complete listing of demo_threadx.c, including the line numbers referenced throughout the remainder of this chapter.

Application Define

The tx_application_define function executes after the basic ThreadX initialization is complete. It is responsible for setting up all of the initial system resources, including threads, queues, semaphores, mutexes, event flags, and memory pools.

The demonstration system’s tx_application_define (line numbers 60-164) creates the demonstration objects in the following order:

  • byte_pool_0

  • thread_0

  • thread_1

  • thread_2

  • thread_3

  • thread_4

  • thread_5

  • thread_6

  • thread_7

  • queue_0

  • semaphore_0

  • event_flags_0

  • mutex_0

  • block_pool_0

The demonstration system does not create any other additional ThreadX objects. However, an actual application may create system objects during runtime inside of executing threads.

Initial Execution

All threads are created with the TX_AUTO_START option. This makes them initially ready for execution. After tx_application_define completes, control is transferred to the thread scheduler and from there to each individual thread.

The order in which the threads execute is determined by their priority and the order that they were created. In the demonstration system, thread_0 executes first because it has the highest priority (it was created with a priority of 1). After thread_0 suspends, thread_5 is executed, followed by the execution of thread_3, thread_4, thread_6, thread_7, thread_1, and finally thread_2.

Note
 Even though thread_3 and thread_4 have the same priority (both created with a priority of 8), thread_3 executes first. This is because thread_3 was created and became ready before thread_4. Threads of equal priority execute in a FIFO fashion.

Thread 0

The function thread_0_entry marks the entry point of the thread (lines 167-190). Thread_0 is the first thread in the demonstration system to execute. Its processing is simple: it increments its counter, sleeps for 10 timer ticks, sets an event flag to wake up thread_5, then repeats the sequence.

Thread_0 is the highest priority thread in the system. When its requested sleep expires, it will preempt any other executing thread in the demonstration.

Thread 1

The function thread_1_entry marks the entry point of the thread (lines 193-216). Thread_1 is the second-to-last thread in the demonstration system to execute. Its processing consists of incrementing its counter, sending a message to thread_2 (through queue_0), and repeating the sequence. Notice that thread_1 suspends whenever queue_0 becomes full (line 207).

Thread 2

The function thread_2_entry marks the entry point of the thread (lines 219-243). Thread_2 is the last thread in the demonstration system to execute. Its processing consists of incrementing its counter, getting a message from thread_1 (through queue_0), and repeating the sequence. Notice that thread_2 suspends whenever queue_0 becomes empty (line 233).

Although thread_1 and thread_2 share the lowest priority in the demonstration system (priority 16), they Threads 3 and 4

are also the only threads that are ready for execution most of the time. They are also the only threads created with time-slicing (lines 87 and 93). Each thread is allowed to execute for a maximum of 4 timer ticks before the other thread is executed.

Threads 3 and 4

The function thread_3_and_4_entry marks the entry point of both thread_3 and thread_4 (lines 246-280). Both threads have a priority of 8, which makes them the third and fourth threads in the demonstration system to execute. The processing for each thread is the same: incrementing its counter, getting semaphore_0, sleeping for 2 timer ticks, releasing semaphore_0, and repeating the sequence. Notice that each thread suspends whenever semaphore_0 is unavailable (line 264).

Also both threads use the same function for their main processing. This presents no problems because they both have their own unique stack, and C is naturally reentrant. Each thread determines which one it is by examination of the thread input parameter (line 258), which is setup when they are created (lines 102 and 109).

Note
 It is also reasonable to obtain the current thread point during thread execution and compare it with the control block’s address to determine thread identity.

Thread 5

The function thread_5_entry marks the entry point of the thread (lines 283-305). Thread_5 is the second thread in the demonstration system to execute. Its processing consists of incrementing its counter, getting an event flag from thread_0 (through event_flags_0), and repeating the sequence. Notice that thread_5 suspends whenever the event flag in event_flags_0 is not available (line 298).

Threads 6 and 7

The function thread_6_and_7_entry marks the entry point of both thread_6 and thread_7 (lines 307-358). Both threads have a priority of 8, which makes them the fifth and sixth threads in the demonstration system to execute. The processing for each thread is the same: incrementing its counter, getting mutex_0 twice, sleeping for 2 timer ticks, releasing mutex_0 twice, and repeating the sequence. Notice that each thread suspends whenever mutex_0 is unavailable (line 325).

Also both threads use the same function for their main processing. This presents no problems because they both have their own unique stack, and C is naturally reentrant. Each thread determines which one it is by examination of the thread input parameter (line 319), which is setup when they are created (lines 126 and 133).

Observing the Demonstration

Each of the demonstration threads increments its own unique counter. The following counters may be examined to check on the demo’s operation:

  • thread_0_counter

  • thread_1_counter

  • thread_2_counter

  • thread_3_counter

  • thread_4_counter

  • thread_5_counter

  • thread_6_counter

  • thread_7_counter

Each of these counters should continue to increase as the demonstration executes, with thread_1_counter and thread_2_counter increasing at the fastest rate.

Distribution file: demo_threadx.c

This section displays the complete listing of demo_threadx.c, including the line numbers referenced throughout this chapter.

/* This is a small demo of the high-performance ThreadX kernel. It includes examples of eight
threads of different priorities, using a message queue, semaphore, mutex, event flags group,
byte pool, and block pool. */

#include "tx_api.h"

#define DEMO_STACK_SIZE 1024
#define DEMO_BYTE_POOL_SIZE 9120
#define DEMO_BLOCK_POOL_SIZE 100
#define DEMO_QUEUE_SIZE 100

/* Define the ThreadX object control blocks... */

TX_THREAD thread_0;
TX_THREAD thread_1;
TX_THREAD thread_2;
TX_THREAD thread_3;
TX_THREAD thread_4;
TX_THREAD thread_5;
TX_THREAD thread_6;
TX_THREAD thread_7;
TX_QUEUE queue_0;
TX_SEMAPHORE semaphore_0;
TX_MUTEX mutex_0;
TX_EVENT_FLAGS_GROUP event_flags_0;
TX_BYTE_POOL byte_pool_0;
TX_BLOCK_POOL block_pool_0;

/* Define the counters used in the demo application... */

ULONG thread_0_counter;
ULONG thread_1_counter;
ULONG thread_1_messages_sent;
ULONG thread_2_counter;
ULONG thread_2_messages_received;
ULONG thread_3_counter;
ULONG thread_4_counter;
ULONG thread_5_counter;
ULONG thread_6_counter;
ULONG thread_7_counter;

/* Define thread prototypes. */

void thread_0_entry(ULONG thread_input);
void thread_1_entry(ULONG thread_input);
void thread_2_entry(ULONG thread_input);
void thread_3_and_4_entry(ULONG thread_input);
void thread_5_entry(ULONG thread_input);
void thread_6_and_7_entry(ULONG thread_input);


/* Define main entry point. */

int main()
{
    /* Enter the ThreadX kernel. */
    tx_kernel_enter();
}

/* Define what the initial system looks like. */
void tx_application_define(void *first_unused_memory)
{

    CHAR *pointer;

    /* Create a byte memory pool from which to allocate the thread stacks. */
    tx_byte_pool_create(&byte_pool_0, "byte pool 0", first_unused_memory,
        DEMO_BYTE_POOL_SIZE);

    /* Put system definition stuff in here, e.g., thread creates and other assorted
        create information. */

    /* Allocate the stack for thread 0. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);

    /* Create the main thread. */
    tx_thread_create(&thread_0, "thread 0", thread_0_entry, 0,
        pointer, DEMO_STACK_SIZE,
        1, 1, TX_NO_TIME_SLICE, TX_AUTO_START);

    /* Allocate the stack for thread 1. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);

    /* Create threads 1 and 2. These threads pass information through a ThreadX
        message queue. It is also interesting to note that these threads have a time
        slice. */
    tx_thread_create(&thread_1, "thread 1", thread_1_entry, 1,
        pointer, DEMO_STACK_SIZE,
        16, 16, 4, TX_AUTO_START);

    /* Allocate the stack for thread 2. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);
        tx_thread_create(&thread_2, "thread 2", thread_2_entry, 2,
        pointer, DEMO_STACK_SIZE,
        16, 16, 4, TX_AUTO_START);

    /* Allocate the stack for thread 3. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);

    /* Create threads 3 and 4. These threads compete for a ThreadX counting semaphore.
        An interesting thing here is that both threads share the same instruction area. */
    tx_thread_create(&thread_3, "thread 3", thread_3_and_4_entry, 3,
        pointer, DEMO_STACK_SIZE,
        8, 8, TX_NO_TIME_SLICE, TX_AUTO_START);

    /* Allocate the stack for thread 4. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);

    tx_thread_create(&thread_4, "thread 4", thread_3_and_4_entry, 4,
        pointer, DEMO_STACK_SIZE,
        8, 8, TX_NO_TIME_SLICE, TX_AUTO_START);

    /* Allocate the stack for thread 5. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);

    /* Create thread 5. This thread simply pends on an event flag, which will be set
        by thread_0. */
    tx_thread_create(&thread_5, "thread 5", thread_5_entry, 5,
        pointer, DEMO_STACK_SIZE,
        4, 4, TX_NO_TIME_SLICE, TX_AUTO_START);

    /* Allocate the stack for thread 6. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);

    /* Create threads 6 and 7. These threads compete for a ThreadX mutex. */
    tx_thread_create(&thread_6, "thread 6", thread_6_and_7_entry, 6,
        pointer, DEMO_STACK_SIZE,
        8, 8, TX_NO_TIME_SLICE, TX_AUTO_START);

    /* Allocate the stack for thread 7. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_STACK_SIZE, TX_NO_WAIT);

    tx_thread_create(&thread_7, "thread 7", thread_6_and_7_entry, 7,
        pointer, DEMO_STACK_SIZE,
        8, 8, TX_NO_TIME_SLICE, TX_AUTO_START);

    /* Allocate the message queue. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_QUEUE_SIZE*sizeof(ULONG), TX_NO_WAIT);

    /* Create the message queue shared by threads 1 and 2. */
    tx_queue_create(&queue_0, "queue 0", TX_1_ULONG, pointer, DEMO_QUEUE_SIZE*sizeof(ULONG));

    /* Create the semaphore used by threads 3 and 4. */
    tx_semaphore_create(&semaphore_0, "semaphore 0", 1);

    /* Create the event flags group used by threads 1 and 5. */
    tx_event_flags_create(&event_flags_0, "event flags 0");

    /* Create the mutex used by thread 6 and 7 without priority inheritance. */
    tx_mutex_create(&mutex_0, "mutex 0", TX_NO_INHERIT);

    /* Allocate the memory for a small block pool. */
    tx_byte_allocate(&byte_pool_0, &pointer, DEMO_BLOCK_POOL_SIZE, TX_NO_WAIT);

    /* Create a block memory pool to allocate a message buffer from. */
    tx_block_pool_create(&block_pool_0, "block pool 0", sizeof(ULONG), pointer,
        DEMO_BLOCK_POOL_SIZE);

    /* Allocate a block and release the block memory. */
    tx_block_allocate(&block_pool_0, &pointer, TX_NO_WAIT);

    /* Release the block back to the pool. */
    tx_block_release(pointer);
}

/* Define the test threads. */
void thread_0_entry(ULONG thread_input)
{
    UINT status;


    /* This thread simply sits in while-forever-sleep loop. */
    while(1)
    {

        /* Increment the thread counter. */
        thread_0_counter++;

        /* Sleep for 10 ticks. */
        tx_thread_sleep(10);

        /* Set event flag 0 to wakeup thread 5. */
        status = tx_event_flags_set(&event_flags_0, 0x1, TX_OR);

        /* Check status. */
        if (status != TX_SUCCESS)
            break;
    }
}


void thread_1_entry(ULONG thread_input)
{
    UINT status;


    /* This thread simply sends messages to a queue shared by thread 2. */
    while(1)
    {
        /* Increment the thread counter. */
        thread_1_counter++;

        /* Send message to queue 0. */
        status = tx_queue_send(&queue_0, &thread_1_messages_sent, TX_WAIT_FOREVER);

        /* Check completion status. */
        if (status != TX_SUCCESS)
            break;

        /* Increment the message sent. */
        thread_1_messages_sent++;
    }
}


void thread_2_entry(ULONG thread_input)
{
    ULONG received_message;
    UINT status;

    /* This thread retrieves messages placed on the queue by thread 1. */
    while(1)
    {
        /* Increment the thread counter. */
        thread_2_counter++;

        /* Retrieve a message from the queue. */
        status = tx_queue_receive(&queue_0, &received_message, TX_WAIT_FOREVER);

        /* Check completion status and make sure the message is what we
        expected. */
        if ((status != TX_SUCCESS) || (received_message != thread_2_messages_received))
            break;

        /* Otherwise, all is okay. Increment the received message count. */
        thread_2_messages_received++;
    }
}


void thread_3_and_4_entry(ULONG thread_input)
{
    UINT status;


    /* This function is executed from thread 3 and thread 4. As the loop
    below shows, these function compete for ownership of semaphore_0. */
    while(1)
    {
        /* Increment the thread counter. */
        if (thread_input == 3)
            thread_3_counter++;
        else
            thread_4_counter++;

        /* Get the semaphore with suspension. */
        status = tx_semaphore_get(&semaphore_0, TX_WAIT_FOREVER);

        /* Check status. */
        if (status != TX_SUCCESS)
            break;

        /* Sleep for 2 ticks to hold the semaphore. */
        tx_thread_sleep(2);

        /* Release the semaphore. */
        status = tx_semaphore_put(&semaphore_0);

        /* Check status. */
        if (status != TX_SUCCESS)
            break;
    }
}


void thread_5_entry(ULONG thread_input)
{
    UINT status;
    ULONG actual_flags;


    /* This thread simply waits for an event in a forever loop. */
    while(1)
    {
        /* Increment the thread counter. */
        thread_5_counter++;

        /* Wait for event flag 0. */
        status = tx_event_flags_get(&event_flags_0, 0x1, TX_OR_CLEAR,
            &actual_flags, TX_WAIT_FOREVER);

        /* Check status. */
        if ((status != TX_SUCCESS) || (actual_flags != 0x1))
            break;
    }
}

void thread_6_and_7_entry(ULONG thread_input)
{
    UINT status;

    /* This function is executed from thread 6 and thread 7. As the loop
        below shows, these function compete for ownership of mutex_0. */
    while(1)
    {
        /* Increment the thread counter. */
        if (thread_input == 6)
            thread_6_counter++;
        else
            thread_7_counter++;

        /* Get the mutex with suspension. */
        status = tx_mutex_get(&mutex_0, TX_WAIT_FOREVER);

        /* Check status. */
        if (status != TX_SUCCESS)
            break;

        /* Get the mutex again with suspension. This shows
            that an owning thread may retrieve the mutex it
            owns multiple times. */
        status = tx_mutex_get(&mutex_0, TX_WAIT_FOREVER);

        /* Check status. */
        if (status != TX_SUCCESS)
            break;

        /* Sleep for 2 ticks to hold the mutex. */
        tx_thread_sleep(2);

        /* Release the mutex. */
        status = tx_mutex_put(&mutex_0);

        /* Check status. */
        if (status != TX_SUCCESS)
            break;

        /* Release the mutex again. This will actually
            release ownership since it was obtained twice. */
        status = tx_mutex_put(&mutex_0);

        /* Check status. */
        if (status != TX_SUCCESS)
            break;
    }
}