Timers Peripheral

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Timers allow precise event scheduling, such as creating delays or setting sampling rates for peripherals.

• Errors
• Functions
  • SensEdu_TIMER_DelayInit
  • SensEdu_TIMER_Delay_us
• Examples
  • Blink_Delay
• Developer Notes
  • Timer occupation
  • Frequency settings

Errors

Main timers error code is 0x10xx. Find the way to display errors in your Arduino sketch here.

An overview of possible errors for timers:

• 0x1000: No Errors
• 0x1001: Unexpected DAC frequency. Maximum possible is 60MHz, refer to these calculations for more details

Functions

SensEdu_TIMER_DelayInit

Initializes the timer used for microsecond delays. Call it once in the setup before using delays.

void SensEdu_TIMER_DelayInit();

SensEdu_TIMER_Delay_us

Pauses program execution for a specified duration (blocking delay).

void SensEdu_TIMER_Delay_us(uint32_t delay_us);

Parameters

• delay_us: Delay duration in microseconds. Maximum: 4,294,967,295 µs.

Examples

Blink_Delay

Blinks a LED using microsecond delays.

1. Include the SensEdu library and declare the LED pin (LED_BUILTIN in this case)
2. Initialize the timer with SensEdu_TIMER_DelayInit()
3. Configure the LED pin as an OUTPUT using pinMode()
4. Use alternating calls to SensEdu_TIMER_Delay_us() and digitalWrite() in the main loop to toggle the LED state.

On Arduino GIGA R1 the built-in LED is active-low: LOW = on, HIGH = off.

#include "SensEdu.h"

uint8_t led = LED_BUILTIN;

void setup() {
    SensEdu_TIMER_DelayInit();

    pinMode(led, OUTPUT);
    digitalWrite(led, LOW);
}

void loop() {
    SensEdu_TIMER_Delay_us(500000);
    digitalWrite(led, HIGH);
    SensEdu_TIMER_Delay_us(500000);
    digitalWrite(led, LOW);
}

Developer Notes

Timer occupation

Peripheral timers (ADC/DAC) are hidden, automatically configured and require no user involvement.

Timer allocation:

• TIM1: ADC sampling
• TIM2: delays
• TIM4: DAC sampling

Avoid reusing occupied timers. Refer to STM32H747 Reference Manual to find free available timers. Be aware, future updates will assign dedicated timers to each ADC/DAC separately, which may occupy your custom timer.

Frequency settings

Timer frequency is dependent on 3 parameters:

• Clock Frequency \((CLK)\)
• Prescaler \((PSC)\): CLK divider
• Period \((ARR)\): Register containing the value up to which the count proceeds

\[TIM_{freq} = \frac{CLK}{PSC + 1} * \frac{1}{ARR + 1}\]

The CLK signal is derived from the APB1 and APB2 Timer Clocks, each running at 240MHz.

Prescaler is set to its minimum value to achieve the finest frequency adjustments, resulting in a step size of \(\frac{1}{120\text{MHz}} \approx 8.33\text{ns}\).

ARR	Period	Frequency
1	16.7ns	60MHz
2	25.0ns	40MHz
3	33.3ns	30MHz
4	41.7ns	24MHz
5	50.0ns	20MHz

When a user specifies a frequency for a DAC or ADC, the target value is automatically rounded to the nearest achievable frequency dictated by the timer’s step. The lower target frequency, the higher the achievable precision.