Watchdog Timer

Driver for using the WDT as a reset or interval timer. More...

Files
file	wdt.h
	Watchdog Timer API.

Enumerations
enum	WDT_CLK_DIV {   WDT_CLK_DIV_32 , WDT_CLK_DIV_64 , WDT_CLK_DIV_128 , WDT_CLK_DIV_256 ,   WDT_CLK_DIV_512 , WDT_CLK_DIV_1024 , WDT_CLK_DIV_2048 , WDT_CLK_DIV_4096 }
	Clock divider settings. More...
enum	WDT_RST { WDT_RST_POWER_ON , WDT_RST_MANUAL }
	Reset signal type. More...

Functions
void	wdt_enable_timer (uint8_t initial_count, uint32_t microsec_period, uint8_t irq_prio, wdt_callback callback, void *user_data)
	Enables the WDT as an interval timer.
void	wdt_enable_watchdog (uint8_t initial_count, WDT_CLK_DIV clk_config, WDT_RST reset_select)
	Enables the WDT in watchdog mode.
uint8_t	wdt_get_counter (void)
	Fetches the counter value.
void	wdt_set_counter (uint8_t value)
	Sets the counter value.
void	wdt_pet (void)
	Resets the counter value.
void	wdt_disable (void)
	Disables the WDT.
int	wdt_is_enabled (void)
	Returns whether the WDT is enabled.

Detailed Description

Driver for using the WDT as a reset or interval timer.

The watchdog timer (WDT) is a special-purpose timer peripheral integrated within the Dreamcast's SH4 CPU.

Warning

At this time, there are no known emulators which are emulating the WDT, as it was never used in commercial games; however, it works perfectly fine on real hardware.

There are two different modes of operation which are supported:

• watchdog mode: counter overflow causes a reset interrupt
• interval timer mode: counter overflow invokes a callback function

To start the WDT in watchdog mode, use wdt_enable_watchdog(). To use the WDT as a general-purpose interval timer, use wdt_enable_timer().

The timer can be stopped in either mode by calling wdt_disable().

See also

Real-Time Clock

Enumeration Type Documentation

WDT_CLK_DIV

enum WDT_CLK_DIV

Clock divider settings.

Denominators used to set the frequency divider for the input clock to the WDT.

Enumerator
WDT_CLK_DIV_32	Period: 41us.
WDT_CLK_DIV_64	Period: 82us.
WDT_CLK_DIV_128	Period: 164us.
WDT_CLK_DIV_256	Period: 328us.
WDT_CLK_DIV_512	Period: 656us.
WDT_CLK_DIV_1024	Period: 1.31ms.
WDT_CLK_DIV_2048	Period: 2.62ms.
WDT_CLK_DIV_4096	Period: 5.25ms.

WDT_RST

enum WDT_RST

Reset signal type.

Specifies the kind of reset to be performed when the WDT overflows in watchdog mode.

Enumerator
WDT_RST_POWER_ON	Power-On Reset.
WDT_RST_MANUAL	Manual Reset.

Function Documentation

wdt_disable()

void wdt_disable

(

void

)

Disables the WDT.

Disables the WDT if it was previously enabled, otherwise does nothing.

See also

wdt_enable_timer(), wdt_enable_watchdog()

wdt_enable_timer()

void wdt_enable_timer	(	uint8_t	initial_count,
		uint32_t	microsec_period,
		uint8_t	irq_prio,
		wdt_callback	callback,
		void *	user_data
	)

Enables the WDT as an interval timer.

Stops the WDT if it was previously running and reconfigures it to be used as a generic interval timer, calling the given callback periodically at the requested interval (or as close to it as possible without calling it prematurely).

Note

The internal resolution for each tick of the WDT in this mode is 41us, meaning a requested microsec_period of 100us will result in an actual callback interval of 123us.

Warning

callback is invoked within an interrupt context, meaning that special care should be taken to not perform any logic requiring additional interrupts. Data that is accessed from both within and outside of the callback should be atomic or protected by a lock.

Parameters

initial_count	Initial value of the WDT counter (Normally 0).
microsec_period	Timer callback interval in microseconds
irq_prio	Priority for the interval timer IRQ (1-15)
callback	User function to invoke periodically
user_data	Arbitrary user-provided data for the callback

See also

wdt_disable()

wdt_enable_watchdog()

void wdt_enable_watchdog	(	uint8_t	initial_count,
		WDT_CLK_DIV	clk_config,
		WDT_RST	reset_select
	)

Enables the WDT in watchdog mode.

Stops the WDT if it was previously running and reconfigures it to be used as a typical watchdog timer, generating a reset interrupt upon counter overflow. To prevent this from happening, the user should be periodically resetting the counter.

Note

Keep in mind the speed of the WDT. With a range of 41us to 5.2ms, the WDT will overflow before a single frame in a typical game.

Parameters

initial_count	Initial value of the WDT counter (Normally 0)
clk_config	Clock divider to set watchdog period
reset_select	The type of reset generated upon overflow

See also

wdt_disable()

wdt_get_counter()

uint8_t wdt_get_counter

(

void

)

Fetches the counter value.

Returns the current 8-bit value of the WDT counter.

Returns

Current counter value

See also

wdt_set_counter()

wdt_is_enabled()

int wdt_is_enabled

(

void

)

Returns whether the WDT is enabled.

Checks to see whether the WDT has been enabled.

Returns

1 if enabled, 0 if disabled

wdt_pet()

void wdt_pet

(

void

)

Resets the counter value.

"Petting" or "kicking" the WDT is the same thing as resetting its counter value to 0.

See also

wdt_set_counter()

wdt_set_counter()

void wdt_set_counter

(

uint8_t

value

)

Sets the counter value.

Sets the current 8-bit value of the WDT counter.

Parameters

value

New value for the counter

See also

wdt_get_counter(), wdt_pet()