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[FreeRTOS Home] [Live FreeRTOS Forum] [FAQ] [Archive Top] [October 2012 Threads] Minor timer setup bugfix for PIC24/dsPIC portPosted by Dave Nadler on October 6, 2012 Hi - My blinking light was running at half speed, and I assumed I'd set up the microprocessor clock wrong. After a couple hours checking all the clock configuration options, I found a small 2x error in the port.c timer setup... Here's the fix: // DRN: Timer clock input is system clock >>> DIVIDED BY 2 <<< // DRN: See DS39704A-page 14-6: bit 1 TCS: // DRN: Timerx Clock Source Select bit: 0 = Internal clock (FOSC/2) // DRN: line below fixed to reflect this... const unsigned long ulCompareMatch = ( ( (configCPU_CLOCK_HZ/2) / portTIMER_PRESCALE ) / configTICK_RATE_HZ ) - 1; // DRN // DRN: Was: const unsigned long ulCompareMatch = ( ( configCPU_CLOCK_HZ / portTIMER_PRESCALE ) / configTICK_RATE_HZ ) - 1;
Note 1: the CPU clock on PIC24F is typically 32MHz, but the instruction clock is always 1/2 this value. The timer input takes the CPU clock/2. Note 2: The CPU clock can be reduced in "Doze Mode" power-saving - this is not provided for in FreeRTOS. Hope this is helpful ! Best Regards, Dave
RE: Minor timer setup bugfix for PIC24/dsPIC portPosted by Richard on October 6, 2012 That is curious - I'm sure I would have noticed that. Can you tell me which PIC part number you are using. Thanks.
Regards.
RE: Minor timer setup bugfix for PIC24/dsPIC portPosted by Dave Nadler on October 10, 2012 I'm using the PIC24FJ32GB004. The documentation for the timer module for PIC24 family is here: http://ww1.microchip.com/downloads/en/DeviceDoc/39704a.pdfSee section 14.3 Register 14-1: TxCON: Type A Time Base Control bit 1 The clock definitions for these parts are a bit confusing: CPU clock is 32MHz, also feeds peripherals (excepting USB). Instruction clock is always half this at 16MHz (unless further divided in DOZE low-power mode). Hope that helps, Thanks, Best Regards, Dave
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