TFM SecureFault Accessing RTC device on V2.5.0-rc1

[4DoorToyota]

Hi, 

I have a PCF8523 RTC on a I2C bus connected on a custom board with a NRF9160 Dev board runing it (Acctinius Iccarus Dev board to be exact). Communicating with it over I2C works perfectly however when trying to communicate with it using the RTC driver present in zephyr for it (only present in  V2.5.0-rc1 at the moment) I get a very hard to figure out error. Upon calling any of the API functions I get thrown to here and the board resets:

void C_SecureFault_Handler(void)
{
    /* A SecureFault may indicate corruption of secure state, so it is essential
     * that Non-secure code does not regain control after one is raised.
     * Returning from this exception could allow a pending NS exception to be
     * taken, so the current solution is to panic.
     */
    tfm_core_panic();
}

__attribute__((naked)) void SecureFault_Handler(void)
{
    EXCEPTION_INFO(EXCEPTION_TYPE_SECUREFAULT);

    __ASM volatile(
        "bl        C_SecureFault_Handler   \n"
        "b         .                       \n"
    );
}

(Listed under tf-m/trusted-firmware-m/platform/ext/common/faults.c) 

The RTC is defined like this under the device tree:

&i2c2 {
	compatible = "nordic,nrf-twim";
	status = "okay";

	clock-frequency = <I2C_BITRATE_FAST>;

	pinctrl-0 = <&i2c2_default>;
	pinctrl-1 = <&i2c2_sleep>;
	pinctrl-names = "default", "sleep";
	lis2dh12_accel: lis2dh12-accel@19 {
		compatible = "st,lis2dh12", "st,lis2dh";
		reg = <0x19>;
		irq-gpios = <&gpio0 28 GPIO_ACTIVE_HIGH>,
			  <&gpio0 29 GPIO_ACTIVE_HIGH>;
	};
	pcf8523: pcf8523@40 {
        compatible = "nxp,pcf8523";
        battery-switch-over = "standard";
        alarms-count = <1>;
        reg = <0x40 >;
    };
};

And I'm calling the api function through a c++ as show here: 

int system_utils::boardRTC::getCurrentTime( time_t *buffer){
    rtc_time rtcBuffer;
    int rslt = rtc_get_time(this->RTCdevice, &rtcBuffer);
    //if ( rslt != 0){ //Error case, propagate up 
    //    return rslt;
    //}
    //*buffer = timeutil_timegm(rtc_time_to_tm(&rtcBuffer));
    return 0;
}

(Note that I've commented out code to narrow it down)

Tracing through with the debug functon and a jtag probe the program jumps immediatly after the call to rtc_get_time to the fault. 

Can anyone help me figure out what is happening here? 

[Sigurd Hellesvik]

Hi,

Communicating with it over I2C works perfectly however when trying to communicate with it using the RTC driver present in zephyr for it

Can you link to the RTC driver you refer to?

Are we talking about an external RTC device that you communicate with over I2C?

Regards,
Sigurd Hellesvik

[4DoorToyota]

The driver is here in the main zephyr repository and is part of the versiion included with NRF V2.5.0-rc1.

https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/rtc/rtc_pcf8523.c

The device however does not implement all of the features present on the device so I have a couple of functions that get the I2C node and then commmunicate with the chip over the bus. Wasn't sure if it was a relevant thing to mention but wanted to give the full picture and it shows that the device is alive and functioning. 

[Sigurd Hellesvik]

TF-M assigned different parts of hardware as secure and others as non-secure.

The error you face could be caused because the driver tries to access a secure part from non-secure code.
The I2C driver should be non-secure, but to check this, could you try some different I2C instances?

Maybe more likely is that it is using some pins designated as secure. Could you try to change the pins and see if you get the same issue?

[4DoorToyota]

Hi, 

Did some digging through the code and turns out I was trying to access the RTC device through:

RTCdevice = DEVICE_DT_GET(DT_NODELABEL(pcf8523));

Which in my hubris I assumed would work instead of splitting the DT_NODELABEL off into a define like the examples show. 

Spliting this up into two different lines with a define completly fixed the problem. 

Thank you very much for taking the time to help me!