Clock Accuracy Circuit (r_cac)

Functions
fsp_err_t	R_CAC_Open (cac_ctrl_t *const p_ctrl, cac_cfg_t const *const p_cfg)
fsp_err_t	R_CAC_StartMeasurement (cac_ctrl_t *const p_ctrl)
fsp_err_t	R_CAC_StopMeasurement (cac_ctrl_t *const p_ctrl)
fsp_err_t	R_CAC_Read (cac_ctrl_t *const p_ctrl, uint32_t *const p_counter)
fsp_err_t	R_CAC_Close (cac_ctrl_t *const p_ctrl)
fsp_err_t	R_CAC_CallbackSet (cac_ctrl_t *const p_ctrl, void(*p_callback)(cac_callback_args_t *), void *const p_context, cac_callback_args_t *const p_callback_memory)

Detailed Description

Driver for the CAC peripheral on RX MCUs. This module implements the CAC Interface.

Overview

The interface for the clock frequency accuracy measurement circuit (CAC) peripheral is used to check a system clock frequency with a reference clock signal by counting the number of measurement clock edges that occur between two edges of the reference clock.

Features

• Supports clock frequency-measurement and monitoring based on a reference signal input
• Reference can be either an externally supplied clock source or an internal clock source
• An interrupt request may optionally be generated by a completed measurement, a detected frequency error, or a counter overflow.
• A digital filter is available for an externally supplied reference clock, and dividers are available for both internally supplied measurement and reference clocks.
• Edge-detection options for the reference clock are configurable as rising, falling, or both.

Configuration

Build Time Configurations for r_cac

The following build time configurations are defined in fsp_cfg/r_cac_cfg.h:

Configuration	Options	Default	Description
Parameter Checking	Default (BSP) Enabled Disabled	Default (BSP)	If selected code for parameter checking is included in the build.

Configurations for Monitoring > Clock Accuracy Circuit (r_cac)

This module can be added to the Stacks tab via New Stack > Monitoring > Clock Accuracy Circuit (r_cac).

Configuration	Options	Default	Description
General > Unit	Must be a valid CAC unit	0	Specify the hardware unit.
Name	Name must be a valid C symbol	g_cac0	Module name.
Reference clock divider	32 128 1024 8192	32	Reference clock divider.
Reference clock source	MCU Specific Options		Reference clock source.
Reference clock digital filter	Disabled Sampling clock=Measuring freq Sampling clock=Measuring freq/4 Sampling clock=Measuring freq/16	Disabled	Reference clock digital filter.
Reference clock edge detect	Rising Falling Both	Rising	Reference clock edge detection.
Measurement clock divider	1 4 8 32	1	Measurement clock divider.
Measurement clock source	MCU Specific Options		Measurement clock source.
Upper Limit Threshold	Value must be a non-negative integer, between 0 to 65535	0	Top end of allowable range for measurement completion.
Lower Limit Threshold	Value must be a non-negative integer, between 0 to 65535	0	Bottom end of allowable range for measurement completion.
Frequency Error Interrupt Priority	MCU Specific Options		CAC frequency error interrupt priority.
Measurement End Interrupt Priority	MCU Specific Options		CAC measurement end interrupt priority.
Overflow Interrupt Priority	MCU Specific Options		CAC overflow interrupt priority.
Callback	Name must be a valid C symbol	NULL	Function name for callback

Clock Configuration

The CAC measurement clock source can be configured as the following:

1. MAIN_OSC
2. SUBCLOCK
3. HOCO
4. MOCO
5. LOCO
6. PCLKB
7. IWDT
8. PLL1 output clock P/Q/R (divided by 16)
9. PLL2 output clock P/Q/R (divided by 16)

The CAC reference clock source can be configured as the following:

1. MAIN_OSC
2. SUBCLOCK
3. HOCO
4. MOCO
5. LOCO
6. PCLKB
7. IWDT
8. External Clock Source (CACREF)
9. PLL1 output clock P/Q/R (divided by 16)
10. PLL2 output clock P/Q/R (divided by 16)

Note:

• For RX74M/RX74N device:
  • SUBCLOCK and LOCO are only used in Unit 0.
  • PLL1 output clock P/Q/R (divided by 16) are only used in Unit 1.
  • PLL2 output clock P/Q/R (divided by 16) are only used in Unit 2.

Pin Configuration

The CACREF pin can be configured to provide the reference clock for CAC measurements.

Usage Notes

Measurement Accuracy

The clock measurement result may be off by up to one pulse depending on the phase difference between the edge detection circuit, digital filter, and CACREF pin signal, if applicable.

Frequency Error Interrupt

The frequency error interrupt is only triggered at the end of a CAC measurement. This means that there will be a measurement complete interrupt in addition to the frequency error interrupt.

Examples

Basic Example

This is a basic example of minimal use of the CAC in an application.

volatile uint32_t g_callback_complete;

void cac_basic_example (void)
{
    g_callback_complete = 0;

    fsp_err_t err = R_CAC_Open(&g_cac_ctrl, &g_cac_cfg);

    /* Handle any errors. This function should be defined by the user. */
    assert(FSP_SUCCESS == err);

    (void) R_CAC_StartMeasurement(&g_cac_ctrl);

    /* Wait for measurement to complete. */
    while (0 == g_callback_complete)
    {
    }

    uint32_t value;

    /* Read the CAC measurement. */
    (void) R_CAC_Read(&g_cac_ctrl, &value);
}

/* Called when measurement is completed. */
static void r_cac_callback (cac_callback_args_t * p_args)
{
    if (CAC_EVENT_MEASUREMENT_COMPLETE == p_args->event)
    {
        g_callback_complete = 1U;
    }
}

Data Structures
struct	cac_instance_ctrl_t
struct	cac_extended_cfg_t

---

Data Structure Documentation

cac_instance_ctrl_t

struct cac_instance_ctrl_t

CAC instance control block. DO NOT INITIALIZE.

cac_extended_cfg_t

struct cac_extended_cfg_t

CAC Extended Configuration

Data Fields
uint32_t	unit	CAC Unit.

Function Documentation

R_CAC_Open()

fsp_err_t R_CAC_Open	(	cac_ctrl_t *const	p_ctrl,
		cac_cfg_t const *const	p_cfg
	)

The Open function configures the CAC based on the provided user configuration settings.

Return values

FSP_SUCCESS	CAC is available and available for measurement(s).
FSP_ERR_ASSERTION	An argument is invalid.
FSP_ERR_ALREADY_OPEN	The CAC has already been opened.
FSP_ERR_IP_UNIT_NOT_PRESENT	Unit does not exist on this MCU.

Note

There is only a single CAC peripheral.

R_CAC_StartMeasurement()

fsp_err_t R_CAC_StartMeasurement

(

cac_ctrl_t *const

p_ctrl

)

Start the CAC measurement process.

Return values

FSP_SUCCESS	CAC measurement started.
FSP_ERR_ASSERTION	NULL provided for p_instance_ctrl or p_cfg.
FSP_ERR_NOT_OPEN	R_CAC_Open() has not been successfully called.

R_CAC_StopMeasurement()

fsp_err_t R_CAC_StopMeasurement

(

cac_ctrl_t *const

p_ctrl

)

Stop the CAC measurement process.

Return values

FSP_SUCCESS	CAC measuring has been stopped.
FSP_ERR_ASSERTION	NULL provided for p_instance_ctrl or p_cfg.
FSP_ERR_NOT_OPEN	R_CAC_Open() has not been successfully called.

R_CAC_Read()

fsp_err_t R_CAC_Read	(	cac_ctrl_t *const	p_ctrl,
		uint32_t *const	p_counter
	)

Read and return the CAC status and counter registers.

Return values

FSP_SUCCESS	CAC read successful.
FSP_ERR_ASSERTION	An argument is NULL.
FSP_ERR_NOT_OPEN	R_CAC_Open() has not been successfully called.

R_CAC_Close()

fsp_err_t R_CAC_Close

(

cac_ctrl_t *const

p_ctrl

)

Release any resources that were allocated by the Open() or any subsequent CAC operations.

Return values

FSP_SUCCESS	Successful close.
FSP_ERR_ASSERTION	NULL provided for p_instance_ctrl or p_cfg.
FSP_ERR_NOT_OPEN	R_CAC_Open() has not been successfully called.

R_CAC_CallbackSet()

fsp_err_t R_CAC_CallbackSet	(	cac_ctrl_t *const	p_ctrl,
		void(*)(cac_callback_args_t *)	p_callback,
		void *const	p_context,
		cac_callback_args_t *const	p_callback_memory
	)

Updates the user callback with the option to provide memory for the callback argument structure. Implements cac_api_t::callbackSet.

Return values

FSP_SUCCESS	Callback updated successfully.
FSP_ERR_ASSERTION	A required pointer is NULL.
FSP_ERR_NOT_OPEN	The control block has not been opened.