TLF35584 SBC Disabling the WWD in NORMAL state

[User22683]

Dear all,

I would like to deactivate the window watchdog, WWD, as soon as it is serviced by the MCU..
I have the following questions:
1.During SBC state INIT, can the WWD be deactivated during the Long Open Windows?
2. After the MCU has serviced the WWD during the Log Open Windows, can the WWD be deactivated immediately? Or does the deactivation have to be timed according to the open window?
3. Could the deactivation of the WWD in SBC INIT state have any repercussions?
4. I am considering the option of deactivating it when in SBC NORMAL state. Even so, does the deactivation have to be timed according to the open window?
5. According to the TLF35584 Datasheet, there is a cycle time for the watchdog (WDCYC). The time of this first Open Window depends on the configured cycle time and is 600 ms (WDCYC = 1) or 60ms (WDCYC = 0).
What does the (WDCYC = 0) 0.1ms and (WDCYC = 1) 1ms tick period mentioned in the TLF35584 Datasheet mean?
How come the electrical characteristics say that the watchdog cycle time is minimum 94us and max 106.5us. I can't get my mind around these three timing definitions.

Your support will be highly appreciated.

[AnilKumar · Accepted solution]

1.During SBC state INIT, can the WWD be deactivated during the Long Open Windows?

The window watchdog will become active in INIT state as soon as reset output pin ROT turns from low to high. However, WWD can be deactivated via SPI command to WDCFG0 register.

2. After the MCU has serviced the WWD during the Log Open Windows, can the WWD be deactivated immediately? Or does the deactivation have to be timed according to the open window?

Window Watchdog in TLF35584 can be disabled by writing the protected registers using UNLOCK- reconfigure - LOCK sequence. Rev 2.0 DS Chapter 13.2 Page 165

WWD disabling via SPI 

DESCRIPTION:

The TLF38884 shall:

• disable WWD
• set register bit RWDCFG0.WWDEN to 0_B

• reflect the WWD configuration values in the following registers
  • RWDCFG0
  • RWDCFG1
  • RWWDCFG0
  • RWWDCFG1

if all the conditions below are met:

• WWDEN is set to 0_Bvia protected SPI communication using UNLOCK and LOCK sequence.
• FSM is in NORMAL state OR FSM is in WAKE state OR (FSM is in INIT state AND ROT has been released)

WWD disabling for SLEEP state 

DESCRIPTION:

The digtoppad shall:

• disable  WWD in SLEEP state
• reflect the WWD configuration values in the following registers
  • RWDCFG0
  • RWDCFG1
  • RWWDCFG0
  • RWWDCFG1

if all the conditions below are met:

• WDSLPEN is set to 0_BOR WDCFG1.WDSLPEN is set to 1_B AND WDCFG0.WWDEN is set to 0_B via protected SPI communication
• FSMis in NORMAL state OR FSM is in WAKE state OR (FSM is in INIT state AND ROT has been released)

Notes:

• Register bits WDCFG1.WDSLPEN AND WDCFG0.WWDEN cannot be changed in SLEEP state

3. Could the deactivation of the WWD in SBC INIT state have any repercussions?

During the initial open window in INIT state the TLF35584 is just waiting for the first trigger according to the default configuration.

Applying a new configuration is also valid in this state without providing a service before. The first service OR re-config OR disable within the Long Open window is mandatory to not run into a Initialization failure. (refer Chapter 15.3 Page 223)
In case the watchdog supervision is disabled, for sure no service is to be provided. 

During operation (active service) of the watchdogs the re-configuration can be done at any time. Locking the new config will start a new configured open window.

During operation, if they are disabling WWD in open window, They should do it before the open window closes or else it will trigger +2 in error counter and Interrupt. Same for closed window, if they don’t finish disabling within closed window, the next open window has to be serviced.

4. I am considering the option of deactivating it when in SBC NORMAL state. Even so, does the deactivation have to be timed according to the open window?

Answered in 3

5. According to the TLF35584 Datasheet, there is a cycle time for the watchdog (WDCYC). The time of this first Open Window depends on the configured cycle time and is 600 ms (WDCYC = 1) or 60ms (WDCYC = 0).
   What does the (WDCYC = 0) 0.1ms and (WDCYC = 1) 1ms tick period mentioned in the TLF35584 Datasheet mean?
   
   

The first open window represents Long open window whose time period is fixed based on the selection of WDCYC=1 or WDCYC=0. i.e. 600ms for WDCYC=1 and 60ms for WDCYC=0.This has nothing to do with the tick period.

Now, (WDCYC = 0) 0.1ms and (WDCYC = 1) 1ms tick period are the minimum Watchdog cycle time. i.e. all configurable fields like Open window, Closed window can be calculated with this tick period. For example, if you want to configure open window time as 50ms, you need 50 cycles with 1ms tick period, i.e. 50*(WDCYC=1) = 50ms

How come the electrical characteristics say that the watchdog cycle time is minimum 94us and max 106.5us. I can't get my mind around these three timing definitions.

When WDCYC is configured as 0, typical watchdog cycle time would be 0.1ms/100us with min as 94us and max 106.5u because of manufacturing tolerances