Microsecond Ticker
[Hal]

Get ticker's data.

Returns:

The microsecond ticker data

Definition at line 84 of file mbed_us_ticker_api.c.

Set ticker IRQ handler.

Parameters:

ticker_irq_handler

IRQ handler to be connected

Returns:

previous ticker IRQ handler

Note:

by default IRQ handler is set to ticker_irq_handler

this function is primarily for testing purposes and it's not required part of HAL implementation

Definition at line 89 of file mbed_us_ticker_api.c.

Clear us ticker interrupt.

Pseudo Code:

 void us_ticker_clear_interrupt(void)
 {
     // Write to the ICR (interrupt clear register) of the TIMER
     TIMER_ICR = TIMER_ICR_COMPARE_Msk;
 }

Disable us ticker interrupt.

Pseudo Code:

 void us_ticker_disable_interrupt(void)
 {
     // Disable the compare interrupt
     TIMER_CTRL &= ~TIMER_CTRL_COMPARE_ENABLE_Msk;
 }

Set pending interrupt that should be fired right away.

The ticker should be initialized prior calling this function.

Pseudo Code:

 void us_ticker_fire_interrupt(void)
 {
     NVIC_SetPendingIRQ(TIMER_IRQn);
 }

Deinitialize the us ticker.

Powerdown the us ticker in preparation for sleep, powerdown, or reset.

After this function is called, no other ticker functions should be called except us_ticker_init(), calling any function other than init is undefined.

Note:

This function stops the ticker from counting.

Pseudo Code:

 uint32_t us_ticker_free()
 {
     // Disable timer
     TIMER_CTRL &= ~TIMER_CTRL_ENABLE_Msk;

     // Disable the compare interrupt
     TIMER_CTRL &= ~TIMER_CTRL_COMPARE_ENABLE_Msk;

     // Disable timer interrupt
     NVIC_DisableIRQ(TIMER_IRQn);

     // Disable clock gate so processor cannot read TIMER registers
     POWER_CTRL &= ~POWER_CTRL_TIMER_Msk;
 }

Get frequency and counter bits of this ticker.

Pseudo Code:

 const ticker_info_t* us_ticker_get_info()
 {
     static const ticker_info_t info = {
         1000000,    // 1 MHz
         32          // 32 bit counter
     };
     return &info;
 }

Initialize the ticker.

Initialize or re-initialize the ticker. This resets all the clocking and prescaler registers, along with disabling the compare interrupt.

Note:

Initialization properties tested by ticker_init_test

Pseudo Code:

 void us_ticker_init()
 {
     // Enable clock gate so processor can read TIMER registers
     POWER_CTRL |= POWER_CTRL_TIMER_Msk;

     // Disable the timer and ensure it is powered down
     TIMER_CTRL &= ~(TIMER_CTRL_ENABLE_Msk | TIMER_CTRL_COMPARE_ENABLE_Msk);

     // Configure divisors
     uint32_t prescale = SystemCoreClock / 1000000;
     TIMER_PRESCALE = prescale - 1;
     TIMER_CTRL |= TIMER_CTRL_ENABLE_Msk;

     // Install the interrupt handler
     NVIC_SetVector(TIMER_IRQn, (uint32_t)us_ticker_irq_handler);
     NVIC_EnableIRQ(TIMER_IRQn);
 }

The wrapper for ticker_irq_handler, to pass us ticker's data.

Definition at line 98 of file mbed_us_ticker_api.c.

Read the current counter.

Read the current counter value without performing frequency conversions. If no rollover has occurred, the seconds passed since us_ticker_init() was called can be found by dividing the ticks returned by this function by the frequency returned by us_ticker_get_info.

Returns:

The current timer's counter value in ticks

Pseudo Code:

 uint32_t us_ticker_read()
 {
     return TIMER_COUNT;
 }

Set interrupt for specified timestamp.

Parameters:

timestamp

The time in ticks to be set

Note:

no special handling needs to be done for times in the past as the common timer code will detect this and call us_ticker_fire_interrupt() if this is the case

calling this function with timestamp of more than the supported number of bits returned by us_ticker_get_info results in undefined behavior.

Pseudo Code:

 void us_ticker_set_interrupt(timestamp_t timestamp)
 {
     TIMER_COMPARE = timestamp;
     TIMER_CTRL |= TIMER_CTRL_COMPARE_ENABLE_Msk;
 }