Nuts and Volts - May/June 2018

Screenshot 1:

// GSM MODULE INIT
 gsm_cmdSingle( “AT” );  //are you there?
 gsm_cmdSingle( “AT” );
 gsm_cmdSingle( “AT” );
 gsm_cmdSingle( “ATE0” ); //turn off echo
 gsm_cmdSingle( “AT+CMGF=1” );  //text
messaging
 // SMS message
 msg[0] = ‘\0’;
 strcat(msg, “Text Message from Design Cycle”);
 strcat(msg, “\r\n”); // Add new line (CR + LF)
 }
/***********************************************
//* HANDLER FOR DATA SENT FROM GSM MODULE UART
//***********************************************
void gsm_default_handler( uint8_t *rsp, uint8_t
*evArgs )
{
 mikrobus_logWrite( rsp, _LOG_TEXT );
 
 
 //  SKIP <CR> and <LF>
 if (0 == strncmp(“RING”, rsp + 2, 4))
 {
 callFlag = 1;
 }
}
//***********************************************
//* APPLICATION INIT
//***********************************************
void applicationInit()
{
// GSM TIMER INIT
 gsm_configTimer();

The timer configuration is easily accomplished using a MikroElektronika application called Timer Calculator (Screenshot 2), which is free for download. As you can see in Screenshot 2, the timer tick is set for one millisecond.

The GSM click is attached to the mikroBUS1 GPIO and UART pins using the gsm_uartDriverInit function, which is part of the GSM click library. The (T_GSM_P) is nothing more than a type, which is defined as a byte pointer in the Click_GSM_types.h file (#define T_GSM_P const uint8_t*).

The default handler is responsible for logging the click UART responses and filtering out the RING indication for incoming calls. The 1500 argument of the gsm_coreInit function call is a watchdog timeout value.

// GSM DRIVER INIT
 gsm_uartDriverInit((T_GSM_P)&_MIKROBUS1_GPIO,
(T_GSM_P)&_MIKROBUS1_UART);
 gsm_coreInit( gsm_default_handler, 1500 );

Following the enabling of hardware flow control (gsm_hfcEnable(true)), we power-up the GSM module and issue some AT commands. The AT commands insure that the GSM click hears us, turns off echo, and sets up for text messaging. Finally, our SMS (Short Message Service) message is defined and we’re ready to rock and roll.

// GSM MODULE POWER ON
 gsm_hfcEnable( true );
 gsm_modulePower( true );

The application task is designed to answer the phone, immediately hang up, and three seconds later send our predetermined text message:

//***********************************************
//* APPLICATION TASK
//***********************************************
void applicationTask()
{
// CORE STATE MACHINE
 gsm_process();
 if (0 != callFlag)
 {
 gsm_cmdSingle( “ATH” );
 Delay_ms( 3000 );
 sendSMSmsg(msg);
 
 
 callFlag = 0;
 }

n SCREENSHOT 2. This handy little app does all of the dirty work and generates a skeleton timer interrupt handler to boot. The preset I selected happened to match the original code.