Timer 3 interrupts issue

Support Wixel
1

Hi i am trying to set up an overflow timer interrupt on Timer 3 The code is getting stuck in the interrupt routine. i am using the 2511F32 (wixel)

Here is the interrupt setting code:

{
    ......

    T3CTL |= 0xE0;                  // set prescaler to tick frequency / 128 (DIV) bits 7:5
    T3CTL |= 0x04;                  // Clear counter value (CLR - bit 2)
    T3CTL |= 0x00;                  // Timer mode set to free running (00) bits 1:0
    T3CTL |= 0x08;                  // Enable overflow interrupt (OVFIM) bit 3
    
    T3CCTL1 &= ~0x40;               // disable timer compare interrupts
    T3CCTL0 &= ~0x40;               // disable timer compare interrupts
    
    IEN1  |= 0x08;                  // Enable Timer 2 interrupts
    
    
    T3CTL |= 0x10;                  // Start the timer (START - bit 4)

    EN = 1;

    ......
}

Here’s the interrupt routine code

ISR(T3,0)
    {
        TIMIF &= ~0x07;      //   T3OVFIF Clear T3 overflow interrupt flag - bit 0
        LED_YELLOW_TOGGLE();
    }

It remains trapped in the ISR routine. There are no other interrupt flags to clear. Any ideas ?

2

How do you know that execution remains trapped in the ISR and on what line is it trapped?

3

Hello.

It looks like the problem is using the yellow led in your interrupt code. The boardService() function calls boardStartBootloaderIfNeeded(), and it will then see that the yellow LED (P2_2) is on. Because it will read P2_2 as high, it will start boardStartBootloader() and go into a boot loader state. Below is a code that toggles the red LED with an overflow timer interrupt on Timer 3. (I also noticed that you had EN = 1 in your interrupt settings code and changed it to EA = 1.)

#include <wixel.h>
#include <usb.h>
#include <usb_com.h>

void timer3Init()
{
    T3CCTL1 = T3CCTL0 = 0;  // Disable timer compare interrupts.
    T3CTL = 0b11111100;     // Configure and start Timer 3.
    T3IE = 1;               // Enable the Timer 3 interrupt.    
    EA = 1;                 // Enable interrupts in general.
}

ISR(T3, 0)
{
    // T3IF is cleared automatically and we don't need to clear T3OVFIF.
    LED_RED_TOGGLE();
}

void main()
{
    systemInit();
    usbInit();
    timer3Init();
    while(1)
    {
        usbShowStatusWithGreenLed();
        boardService();
        usbComService();
    }
}

-Jeremy

4

Thank you Jeremy, that was the problem, it was entering boat loader mode, good catch ! - maybe agood idea to add this to the wixel documentation, so you dont cause this “accidents” when using that pin as I/O. This is a great controller, so many peripherals and options, you guys should promote it more, it is very capable and flexible.

5

Hello. I would like to add that you can use the yellow LED pin (P2_2) as an I/O line, but if you do it from an interrupt then you should avoid calling boardService().

–David

6

What do i lose by not calling boardservice ?

7

If you don’t call boardService, then app will no longer detect you shorting P2_2 to 3V3 and launch the bootloader. That shouldn’t be a big problem, because there are two other ways to get into bootloader mode: a USB command, and shorting those pins together when the board starts up. The source code of boardService is pretty simple so I would just recommend reading it:

github.com/pololu/wixel-sdk/blo … el/board.c

–David