Lab 3. Tick Interface Using Timer1

Ensure you are running the VS Code profile created in Lab 0 (MCHP Dev).

Create a basic empty project having a default main.c file.

Create Program Project and Debug Project launch configurations in launch.json.

Perform a build of this project (Ctrl + Shift + B), and verify a successful build.

Open main.c and replace the default application code with the contents below (copy/paste).

/* * File: main.c * Project: lab3 * * Description: * * Create a simple "Tick" interface that enables non-blocking delays using 1mS Timer1 * interrupts. * * The main application toggles the Red RGB LED every 100mS and prints a status * message to the terminal every 1000mS in a non-blocking fashion. * * "Tick" Interface Description * - Defines a TICK type (uint32_t), providing delays from 1mS to ~49 days * - Each TICK increment is 1mS, performed in the Timer 1 ISR * - Defines a macro TICK_SECOND * - Defines a retrieval function, "tickGet()" * * Using the interface (see main() below): * - Store next timeout value using tickGet() * - Compare tickGet() to set timeout * - Use TICK_SECOND for easy reference * */ #include <xc.h> #include <stdio.h> #include <stdint.h> #define FCPU 8000000U #define FPB_FAST FCPU #define FPB_STD FCPU/2 #define FPB_SLO FCPU/4 #define UART_BAUD 9600 // Options @ 8MHz FCPU: 9600, 19200, 38400 #define TICKS_PER_SECOND 1000 // 32-bit counter driven by 1mS Timer1 interrupt #define TICK_SECOND ((uint64_t)TICKS_PER_SECOND) // represents one second in Ticks #pragma config FWDT_WDTEN = SW typedef uint32_t TICK; // all TICKS are stored as 32-bit unsigned integers TICK ledTimeout, printTimeout; // define TICK timeout variables static volatile TICK oneMsCounter; // TICK counter incremented in Timer1 ISR void clocksInit(void); void pinsInit(void); void uartInit(void); void uartWrite(unsigned char txData); unsigned char uartRead(void); void timer1Init(void); TICK tickGet(void); // Timer1 ISR function - increments the global TICK counter every 1mS void __attribute__((interrupt)) _T1Interrupt(void) { IFS1bits.T1IF = 0; // acknowledge/clear interrupt flag oneMsCounter++; // increment the global TICK counter } int main(void) { INTCON1bits.GIE = 0; // prevents interrupt flooding since reset state is a '1' clocksInit(); // initialize all clocks pinsInit(); // initialize all pins uartInit(); // initialize uart peripheral for printf() timer1Init(); // initialize Timer1 for use with "Tick" API INTCON1bits.GIE = 1; // enable global interrupts printf("\r\ndsPIC33A Hands On Labs - Lab 3\r\n\r\n"); ledTimeout = tickGet() + TICK_SECOND/10; // set next 100mS LED toggle timeout value printTimeout = tickGet() + TICK_SECOND/1; // set next 1000mS printf() timeout value while(1) { // is it time to toggle the led ? if((int32_t)(tickGet() - ledTimeout) > (int32_t)0) { LATDbits.LATD9 ^= 1; // toggle the led ledTimeout = tickGet() + TICK_SECOND/10; // set next 100mS LED toggle timeout value } // is it time to print the next message ? if((int32_t)(tickGet() - printTimeout) > (int32_t)0) { printf("Tick: %d\r\n", (TICK)tickGet()); // print the current TICK value printTimeout = tickGet() + TICK_SECOND/1; // set next 1000mS printf() timeout value } } } void clocksInit(void) { /*** System Clocks Initialization ***/ // The FRC provides the source clock // Instruction Clock, Fcpu = 8 MHz // Peripheral Bus Clocks: Fpb_fast = 8 MHz, Fpb_std = 4 MHz, Fpb_slow = 2 MHz // Clock settings left at defaults listed above } void pinsInit(void) { /*** Digital I/O Initialization ***/ // Initialize RGB Red LED pin LATDbits.LATD9 = 0; TRISDbits.TRISD9 = 0; // Initialize Switch S2 input ANSELFbits.ANSELF0 = 0; // disable analog function TRISFbits.TRISF0 = 1; // make pin digital input /*** PPS Initialization ***/ // UART1 TX Assigned to RH0/RP113 (P102_UART_PKOB_TX) RPOR28bits.RP113R = 19; // UART1 RX Assigned to RD10/RP59 (P100_UART_PKOB_RX) RPINR13bits.U1RXR = 59; } void uartInit(void) { unsigned long brg; brg = (FCPU/UART_BAUD/4-1)/2; U1BRG = (unsigned short)brg; U1CON = 0; U1STAT = 0; U1CONbits.BRGS = 1; U1CONbits.TXEN = 1; U1CONbits.RXEN = 1; U1CONbits.ON = 1; } void uartWrite(unsigned char txData){ while(U1STATbits.TXBE == 0); U1TXB = (unsigned long)txData; } unsigned char uartRead(){ while(U1STATbits.RXBE != 0); return U1RXB; } void timer1Init(void) { // Initialize Timer 1 to generate priority level 1 interrupts every 1 mS T1CON = 0x0; TMR1 = 0x0; PR1 = FPB_STD/1000; // set interrupt period to 1mS, given Timer1 CLK IPC6bits.T1IP = 1; // set interrupt priority = 1 IFS1bits.T1IF = 0; // clear interrupt flag IEC1bits.T1IE = 1; // enable Timer1 interrupts T1CONbits.ON = 1; // turn on Timer1 } TICK tickGet(void) { TICK temp; IEC1bits.T1IE = 0; // disable the Timer1 interrupt temp = (TICK)oneMsCounter; // get a clean copy of counter variable IEC1bits.T1IE = 1; // re-enable Timer1 interrupt return temp; // return the current value of the 1mS TICK counter } // support for printf() int __attribute__((__section__(".libc.write"))) write(int handle, void *buffer, unsigned int len){ unsigned char *pData = (unsigned char*)buffer; unsigned short count; for(count=0; count<len; count++) { uartWrite(*pData++); } return count; } int __attribute__((__section__(".libc.read"))) read(int handle, void *buffer, unsigned int len){ unsigned char *pData = (unsigned char*)buffer; unsigned short count; for(count=0; count<len; count++) { *pData++ = uartRead(); } return count; }

Press Ctrl + Shift + B to build the project. 

Fix any syntax errors, ensuring that the project builds successfully:

Launch the program configuration by navigating to Run and Debug and selecting Program Project:

Verify that the program operation was successful:

Click on the SERIAL MONITOR tab in the output window:

Select the PICKit™ 4 COM port. Set the Baud rate to 9600. Press Start Monitoring:

Press the MCLR button on the development board to reset the application. You should see the following messages:

The value of the 1 ms tick counter should be periodically displayed in the serial terminal window.

You should also see the red RGB LED toggling every 100 ms: