ARM Embedded Tutorial - Simple Timer

From Free Pascal wiki
Jump to navigationJump to search
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.

Deutsch (de) English (en)

Simple timer function

In this example, a simple timer for an STM32F103C is used. This microcontroller has 4 timers and you can use timers 2-4 very easily. Timer 1 has several options, so it is more complicated to use.

Program head

program Timer_Blink;

uses
  cortexm3;

Constants and identifiers

const
  TIM_CR1_CEN : uInt16 = $0001;            // Counter enable
  RCC_APB1ENR_TIM2EN : uInt32 = $00000001; // TIM2 clock enabled

  TIM_DIER_CC1IE : uInt16 = $0002;         // Capture / Compare 1 interrupt enable
  TIM_SR_CC1IF : uInt16 = $0002;           // Capture / Compare 1 interrupt flag
  TIM2_IRQn = 28;                          // TIM2 global interrupt

  // For easy access to the LED PC13.
  Type
    TLed = bitpacked array[0..15] of boolean;

var
  LedC : TLed absolute GPIOC.ODR;

Interrupt function

procedure Timer2_Interrupt; public name 'TIM2_global_interrupt';  interrupt;
  begin
    TIM2.SR  := TIM2.SR and not TIM_SR_CC1IF; // Clear CC1IF
    LedC[13] := not LedC[13];                 // Toggle LED PC13
  end;

Main program and initialization

With TIM2.PSC and TIM2.ARR you can set the speed of the timer, the smaller the values, the faster it runs.

  begin
    // Turn on ports
    RCC.APB2ENR := RCC.APB2ENR or (%111 shl 2);

    // Switch ports to output
    GPIOC.CRL := $33333333;
    GPIOC.CRH := $33333333;

    // --- timer ---
    // RCC enable for Timer2
    RCC.APB1ENR := RCC.APB1ENR or RCC_APB1ENR_TIM2EN;

    // Various default settings
    TIM2.CR1   := $0000;  // Control register 1;  Wait with timer enable until settings complete
    TIM2.CR2   := $0000;  // Control register 2
    TIM2.CCMR1 := $0000;  // Capture / compare mode register
    TIM2.CCER  := $0000;  // Capture / compare enable register

    // Prescaler
    TIM2.PSC := 1000;

    // AutoReload value
    TIM2.ARR := 1000;

    // DMA and interrupt control register
    TIM2.DIER := TIM_DIER_CC1IE;  // Compare 1 interrupt enable

    // Enable counter
    TIM2.CR1 := TIM2.CR1 or TIM_CR1_CEN;

    // NVIC configuration
    NVIC.IP[TIM2_IRQn] := $20;    // IRQ priority, right 4 bits always to be zero
    NVIC.ISER[TIM2_IRQn shr 5] := 1 shl (TIM2_IRQn and $1F);  // Enable interrupt

    // --- main loop ---
    while True do begin
      // Do something
    end;
 end.

Multiple timers

You can use 3 simple timers in parallel. These are Timer2 to Timer4. Timer1 is used differently. If you want to use timers 3 and 4, you simply have to replace TIM2 with TIM3 and/or TIM4.

See also