Why we must use a mutex to access the GLCD

How to do it…

To access the GLCD using mutual exclusion, follow the steps outlined:

  1. Create a new project and using the manager configure the RTE to provide support for the Graphic LCD.
  2. Create a new file named RTXBlinky.c, add the boilerplate code, and then add this source file to the project.
  3. Add the following code to RTXBlinky.c:
    #include "stm32f4xx_hal.h"        /* STM32F4xx Defs */
#include "RTXBlinkyUtils.h"
#include "cmsis_os.h"

osThreadId tid_taskA;       /* id of thread: task_a */
osThreadId tid_taskB;       /* id of thread: task_b */

osMutexId mut_GLCD; /* Mutex to control GLCD access */

/*--------------------------------------------------
 *      Switch LED on
 *--------------------------------------------------*/
void switch_On (unsigned char led) {

  osMutexWait(mut_GLCD, osWaitForever);
  GLCD_SetBackgroundColor (GLCD_COLOR_WHITE);
  GLCD_SetForegroundColor(GLCD_COLOR_RED);
  GLCD_SetFont (&GLCD_Font_16x24);
  GLCD_DrawChar(led+(7*16), 4*24, 0x80+1); 
  osMutexRelease(mut_GLCD);
}

/*--------------------------------------------------
 *      Switch LED off
 *--------------------------------------------------*/
void switch_Off (unsigned char led) {

  osMutexWait(mut_GLCD, osWaitForever);
  GLCD_SetBackgroundColor (GLCD_COLOR_WHITE);             
  GLCD_SetForegroundColor(GLCD_COLOR_RED);   
  GLCD_SetFont (&GLCD_Font_16x24);
  GLCD_DrawChar(led+(7*16), 4*24, 0x80+0);     
  osMutexRelease(mut_GLCD);
}

/*--------------------------------------------------
 *      Thread 1 'taskA': Switch LED ON
 *--------------------------------------------------*/
void taskA (void const *argument) {
  for (;;) {
    osSignalWait(0x0001, osWaitForever);    
    switch_On(LED_A);
    osDelay(500);
    osSignalSet(tid_taskB, 0x0001); /* signal taskB */
  }
}

/*--------------------------------------------------
 *      Thread 2 'taskB': Switch LED OFF
 *--------------------------------------------------*/
void taskB (void const *argument) {
  for (;;) {
    osSignalWait(0x0001, osWaitForever); 
    switch_Off(LED_A);
    osDelay(500);
    osSignalSet(tid_taskA, 0x0001); /* signal taskA */
  }
}

osMutexDef(mut_GLCD);

osThreadDef(taskA, osPriorityNormal, __FI, 0);
osThreadDef(taskB, osPriorityNormal, __FI, 0);

/*--------------------------------------------------
 *      Main: Initialize and start RTX Kernel
 *--------------------------------------------------*/
int main (void) {

  HAL_Init ();   /* Init Hardware Abstraction Layer */
  SystemClock_Config ();           /* Config Clocks */        

  GLCD_setup();

  mut_GLCD = osMutexCreate(osMutex(mut_GLCD));

  tid_taskA = osThreadCreate(osThread(taskA), NULL);
  tid_taskB = osThreadCreate(osThread(taskB), NULL);

  osSignalSet(tid_taskA, 0x0001);    /* signal taskA */

  osDelay(osWaitForever);
  while(1);
}
  4. Create the RTXBlinkyUtils.c file, enter the following code, and add this to the project:
    #include "RTXBlinkyUtils.h"

void GLCD_setup(void) {

  unsigned char led;

  GLCD_Initialize();               /* Initialize and */
  GLCD_SetBackgroundColor (GLCD_COLOR_WHITE);
  GLCD_ClearScreen ();             /* clear the GLCD */
  GLCD_SetBackgroundColor(GLCD_COLOR_BLUE);
  GLCD_SetForegroundColor(GLCD_COLOR_WHITE);
  GLCD_SetFont (&GLCD_Font_16x24);
  GLCD_DrawString(0, 0*24, " CORTEX-M4 COOKBOOK ");
  GLCD_DrawString(0, 1*24, "  PACKT Publishing  ");
  GLCD_SetBackgroundColor(GLCD_COLOR_WHITE);
  GLCD_SetForegroundColor(GLCD_COLOR_RED);
  for (led=LED_A; led<LED_G+1; led++)
      GLCD_DrawChar((led+7)*16, 4*24, 0x80+0); 
}
  5. Modify RTXBlinkyUtils.h (defined in the previous recipe), accordingly.
  6. Build, download, and run the program.

How it works…

Calls to GLCD functions within switch_Off() and switch_On() are protected by mut_GLCD, thus enforcing mutual exclusion. The mut_GLCD variable is declared as follows:

osMutexId mut_GLCD;   /* Mutex to control GLCD access */

We also need to register the semaphore by including the following statement:

osMutexDef(mut_GLCD);

We initialize this statement within main() by including the following:

mut_sharedVar = osMutexCreate(osMutex(mut_GLCD));
..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
18.117.99.71