LPC55S69: CPU lockup while accessing to SYSCON

[raz3l]

Hi everyone,

I'm running Zephyr (compiled as Non-Secure) on an LPC55S69, flashed at address 0x0. To boot it, I:

1. Flashed the NS image at 0x0

2. Manually set the PC via GDB

The system only works if I comment out this clock initialization line:

CLOCK_AttachClk(kFRO_HF_to_MAIN_CLK);

Otherwise, it triggers a processor LOCKUP without any visible exception details. I have checked that SAU and MPU are disabled and I have reviewed the Secure AHB Controller (no obvious blocking configurations).

1. Could a platform-level firewall (e.g., peripheral access control) block this clock register?
2. Are there other hardware protections I might have missed?

Thanks!

[Harry_Zhang]

Hi @raz3l 

Yes, the LPC55S69 has platform-level security mechanisms that could be restricting access to the clock registers when running in Non-Secure mode.

BR

Harry

[raz3l]

Hi @Harry_Zhang ,

Could you point me to which platform-level security mechanisms are you referring to?

[Harry_Zhang]

Hi @raz3l 

On the LPC55S69, the platform-level security mechanisms that control peripheral access between Secure and Non-Secure worlds (enabled by ARM TrustZone-M)

Secure AHB Controller (SECURE_AHB / AHB_SECURE_CTRL)

Security access rules for AHB peripherals
Security access rules for AHB peripherals on AHB Slave Port P8. Each peripheral can
have independent security attribute.

Registers: SEC_CTRL_AHB_PORTx_SLAVEy_RULE
These determine whether each peripheral (e.g., SYSCON, CLOCK, IOCON, GPIO) is accessible by:
You can try to test it.

BR

Harry

[raz3l]

Thanks!