SAFE MODE Behavior in MPC5746C

[AshokSubramani]

I have configured the safe mode according as per the attached diagram below. When the ECU enters SAFE MODE, the MCU recovers at the next power cycle only , it cannot be recovered in same cycle ( does this expected..?). Using SIUL2_MSCR[SMC], I can retain the output pin state according to the application or ASIL requirements.

My question is:

• During SAFE MODE, does the application code continue running?

•  are only the I/O pins held in their last state(SMC==1) or high-impedance(SMC==0).

I’m trying to understand this because:

• I’m not seeing any CAN messages transmitted while in SAFE MODE.

• I can’t connect to the MCU with Trace32 during SAFE mode.

If the application does continue running in SAFE MODE, how can I use Trace32 to debug in that mode? or During SAFE MODE the application will be halted & there will be no communication or trace32 access.

[davidtosenovjan]

Certainly yes, but it is needed to realize that during SAFE mode, device is clocked by IRC what’s may affect communication peripherals.

Also pay attention to following note

davidtosenovjan_0-1748863858647.png

I don’t think there would be an issue to debug in TRACE32 when device is in SAFE mode.

[AshokSubramani]

I have attached the used configuration for your reference, since i tried to change the system system clock switch as PLL_PHI0 , but it is not working. what the recommended configuration for the safe mode configuration.

My CAN clock is configured with F40, due to that my can communication is not working..? To support CAN communication in safe mode what configurations have to do..?  

once safe mode is triggered, i cannot able to access any peripherals via trace32, it shows (lpm-st/sl (safe mode). i can't identify whether my system is running or not during safe mode.

AshokSubramani_0-1748866777098.png

AshokSubramani_1-1748867290478.png

[davidtosenovjan]

Apparently this bit should not be set.

davidtosenovjan_0-1748934251890.png

[AshokSubramani]

If i not set the PDO bit, what is the purpose of SAFE Mode..? As per the safety manual, we need to set the PDO bit to initiate the safe mode . Also, i cannot able to disable the PDO bit in safe mode. 

Query :

1. During SAFE mode does application still can control the I/O pins..? if yes, how to configure

2. Why i cannot able to see the trace 32 during safe mode..?

AshokSubramani_0-1748937019398.png

[davidtosenovjan]

You can configure it individually for every pin.

davidtosenovjan_0-1748948377514.png

[AshokSubramani]

I’m unable to set the PD0 bit to  "0" in the SAFE mode configuration because the configurator does not allow me to disable the PD0 bit. during validation process it fails.

[davidtosenovjan]

MC_ME_SAFE_MC[PDO] should be writable, unlike other modes. So I would see it as a configurator issue.

[AshokSubramani]

i tried changing manually (PD0=0) there is no difference in the operation ,  i am getting the below error if i stop running the execution in trace32. It seems that there is no application code running during safe mode. what is the expected behavior in SAFE_MODE...? 

AshokSubramani_0-1748953011213.png

[davidtosenovjan]

Adding @rweiss 

Do you know whether there is known issue with debugging when device is in SAFE mode? Thnks

[AshokSubramani]

If PDO bit is on, ECU is entering into low power mode

Now, i can able to debug from trace32. After disabling the PDO bit.

I have a few questions regarding the clock behavior in SAFE mode:

I configured MC_CGM.AC5_SC[SELCTL] = FXOSC to use a stable external clock source. However, when the software enters SAFE mode, the system automatically switches to the FIRC clock as controlled by the MC_ME module. Even after entering SAFE mode, MC_CGM.AC5_SC[SELCTL] still reports FXOSC as the selected source.

So my questions are:

• Do I need to manually reconfigure the clock source to FIRC after the device enters SAFE mode?

• Or is this unnecessary since SAFE mode automatically forces the internal RC oscillator regardless of the CGM settings?

Additionally, I noticed that MC_CGM.SC_SS[SWTRG] = 0b100, meaning:

“Switch to 16 MHz internal RC oscillator due to SAFE mode request or reset succeeded.”

Also, During SAFE mode why CAN communication is not working when it enters safe mode. Does this is the default action from microcontroller..?