LPTimer (Low-Power Timer)

General Description

High level interface for interacting with the low-power timer (LPTimer).

LPTimer can operate in all possible low power modes. It can be used either to measure timing between events, or to perform some action after a specified interval of time.

Features

• Wake the device up from deepsleep
• Configurable to create a free-running timer or generate periodic interrupts.
• Configurable to update the match value of an already configured LPTimer set up to generate an interrupt on match.
• Used for measuring time between events in free-running mode.

Quick Start

See Snippet 2: LPTimer interrupts.

Code snippets

Snippet 1: LPTimer initialization with Default configuration

The following snippet initializes a LPTimer in free running mode.

    cy_rslt_t           rslt;
    mtb_hal_lptimer_t   lptimer;
    uint32_t            lptimer_value;
 
    // Initialize the LPTIMER with configurator-generated structures
    rslt = mtb_hal_lptimer_setup(&lptimer, &lptimer_hal_config);
    if (CY_RSLT_SUCCESS == rslt)
    {
        rslt = (cy_rslt_t)Cy_MCWDT_Init(lptimer_obj.base, &lptimer_config);
        // Initialize hardware via PDL call (abstracted out)
        _Cy_MCWDT_Enable_IP_Specifc(lptimer_obj.base);
    }
 
    // Read the LPTIMER count value
    lptimer_value = mtb_hal_lptimer_read(&lptimer);

Snippet 2: LPTimer interrupts

The following snippet initializes a LPTimer and uses mtb_hal_lptimer_set_delay() to trigger an interrupt on match. Subsequent interrupts can be triggered at required times using mtb_hal_lptimer_set_delay() called from the ISR.

 
#define LPTIMER_MATCH_VALUE    (8192u)
mtb_hal_lptimer_t lptimer_obj;
// Structures generated by configurator:
const mtb_hal_lptimer_configurator_t lptimer_hal_config;
const cy_stc_mcwdt_config_t lptimer_config;
 
cy_rslt_t snippet_lptimer_init(void)
{
    cy_rslt_t rslt;
 
    // Initialize the LPTIMER
    rslt = mtb_hal_lptimer_setup(&lptimer_obj, &lptimer_hal_config);
    if (CY_RSLT_SUCCESS == rslt)
    {
        rslt = (cy_rslt_t)Cy_MCWDT_Init(lptimer_obj.base, &lptimer_config);
        // Initialize hardware via PDL call (abstracted out)
        _Cy_MCWDT_Enable_IP_Specifc(lptimer_obj.base);
    }
 
    if (CY_RSLT_SUCCESS == rslt)
    {
        // Register the callback handler which will be invoked when the interrupt triggers
        mtb_hal_lptimer_register_callback(&lptimer_obj, lptimer_interrupt_handler, NULL);
 
        // Configure and Enable the LPTIMER events
        mtb_hal_lptimer_enable_event(&lptimer_obj, MTB_HAL_LPTIMER_COMPARE_MATCH, true);
    }
 
    return rslt;
}
 
 
void lptimer_interrupt_handler(void* handler_arg, mtb_hal_lptimer_event_t event)
{
    CY_UNUSED_PARAMETER(handler_arg);
    CY_UNUSED_PARAMETER(event);
    // Reload/Reset the Low-Power timer to start counting from this instant
    mtb_hal_lptimer_set_delay(&lptimer_obj, LPTIMER_MATCH_VALUE);
    mtb_hal_lptimer_process_interrupt(&lptimer_obj);
}
 
 

API Reference
	LPTimer HAL Results
	LPTimer specific return codes.

Typedefs
typedef void(*	mtb_hal_lptimer_event_callback_t) (void *callback_arg, mtb_hal_lptimer_event_t event)
	Handler for LPTimer interrupts.

Enumerations
enum	mtb_hal_lptimer_event_t { MTB_HAL_LPTIMER_COMPARE_MATCH }
	LPTimer interrupt triggers.

Functions
cy_rslt_t	mtb_hal_lptimer_setup (mtb_hal_lptimer_t *obj, const mtb_hal_lptimer_configurator_t *config)
	Sets up a HAL instance to use the specified hardware resource. More...
cy_rslt_t	mtb_hal_lptimer_set_delay (mtb_hal_lptimer_t *obj, uint32_t delay)
	Update the match/compare value. More...
uint32_t	mtb_hal_lptimer_read (const mtb_hal_lptimer_t *obj)
	Read the current tick. More...
void	mtb_hal_lptimer_register_callback (mtb_hal_lptimer_t *obj, mtb_hal_lptimer_event_callback_t callback, void *callback_arg)
	Register a LPTimer match event handler. More...
void	mtb_hal_lptimer_enable_event (mtb_hal_lptimer_t *obj, mtb_hal_lptimer_event_t event, bool enable)
	Configure and Enable/Disable the LPTimer events. More...
cy_rslt_t	mtb_hal_lptimer_process_interrupt (mtb_hal_lptimer_t *obj)
	Process interrupts related related to an LPTimer instance. More...

Function Documentation

mtb_hal_lptimer_setup()

cy_rslt_t mtb_hal_lptimer_setup	(	mtb_hal_lptimer_t *	obj,
		const mtb_hal_lptimer_configurator_t *	config
	)

Sets up a HAL instance to use the specified hardware resource.

This hardware resource must have already been configured via the PDL.

Parameters

[out]	obj	The HAL driver instance object. The caller must allocate the memory for this object, but the HAL will initialize its contents
[in]	config	The configurator-generated HAL config structure for this peripheral instance

Returns

the status of the HAL setup

mtb_hal_lptimer_set_delay()

cy_rslt_t mtb_hal_lptimer_set_delay	(	mtb_hal_lptimer_t *	obj,
		uint32_t	delay
	)

Update the match/compare value.

Update the match value of an already configured LPTimer set up to generate an interrupt on match delay from the current counter value. Note that this function does not reinitialize the counter or the associated peripheral initialization sequence.

Parameters

[in]	obj	The LPTimer object
[in]	delay	The ticks to wait. The minimum permitted delay value can be found in the implementation specific documentation.

Returns

The status of the set_delay request. On success it returns CY_RSLT_SUCCESS.

• 16 bit Counter0 (C0) & Counter1 (C1) are cascaded to generated a 32 bit counter.
• Counter2 (C2) is a free running counter.
• C0 continues counting after reaching its match value.
• An interrupt is generated when C1 increments past the match value.

EXAMPLE: Supposed T=C0=C1=0, and we need to trigger an interrupt at T=0x18000. We set C0_match to 0x8000 and C1 match to 1. At T = 0x8000, C0_value matches C0_match so C1 get incremented. C1/C0=0x18000. At T = 0x18000, C0_value matches C0_match again so C1 get incremented from 1 to 2. When C1 get incremented from 1 to 2 the interrupt is generated. At T = 0x18000, C1/C0 = 0x28000.

mtb_hal_lptimer_read()

uint32_t mtb_hal_lptimer_read

(

const mtb_hal_lptimer_t *

obj

)

Read the current tick.

If no rollover has occurred, the seconds passed since mtb_hal_lptimer_init() or mtb_hal_lptimer_set_time() was called can be found by dividing the ticks returned by this function by the frequency of the source clock (Refer to BSP Settings section in the kit's BSP API Reference Manual for details on the clock source for LPTimer).

Parameters

[in]

obj

The LPTimer object

Returns

The timer's timer value in ticks

mtb_hal_lptimer_register_callback()

void mtb_hal_lptimer_register_callback	(	mtb_hal_lptimer_t *	obj,
		mtb_hal_lptimer_event_callback_t	callback,
		void *	callback_arg
	)

Register a LPTimer match event handler.

This function will be called when one of the events enabled by mtb_hal_lptimer_enable_event occurs.

Parameters

[in]	obj	The LPTimer object
[in]	callback	The callback handler which will be invoked when the interrupt triggers
[in]	callback_arg	Generic argument that will be provided to the handler when called

mtb_hal_lptimer_enable_event()

void mtb_hal_lptimer_enable_event	(	mtb_hal_lptimer_t *	obj,
		mtb_hal_lptimer_event_t	event,
		bool	enable
	)

Configure and Enable/Disable the LPTimer events.

When an enabled event occurs, the function specified by mtb_hal_lptimer_register_callback will be called.

Parameters

[in]	obj	The LPTimer object
[in]	event	The LPTimer event type
[in]	enable	True to turn on event, False to turn off

mtb_hal_lptimer_process_interrupt()

cy_rslt_t mtb_hal_lptimer_process_interrupt

(

mtb_hal_lptimer_t *

obj

)

Process interrupts related related to an LPTimer instance.

Parameters

[in]

obj

HAL object for which the interrupt should be processed

Returns

CY_RSLT_SUCCESS if the interrupt was processed successfully; otherwise an error