Kscan callback triggers fault during interrupt handling

Question

Application is communicating with a touch controller (FT5336) over I2C and registering a callback with kscan_config() and kscan_enable_callback(). Every few minutes a "ZEPHYR FATAL ERROR 0: CPU exception on CPU 0" (Fault during interrupt handling) occurs, restarting the application. Using debug I can see two "<signal handler called>" (photo'd) and I always see a call to "i2c_dump_msgs()" as the lowest call.

J-Link output:

[00:01:00.193,847] <err> os: ***** MPU FAULT *****
[00:01:00.193,878] <err> os: Data Access Violation
[00:01:00.193,878] <err> os: MMFAR Address: 0x4
[00:01:00.193,908] <err> os: r0/a1: 0x20006740 r1/a2: 0x00000000 r2/a3: 0x20000984
[00:01:00.193,908] <err> os: r3/a4: 0x00000000 r12/ip: 0x00000000 r14/lr: 0x00038ed9
[00:01:00.193,939] <err> os: xpsr: 0x21000221
[00:01:00.193,939] <err> os: Faulting instruction address (r15/pc): 0x00038d4e
[00:01:00.193,969] <err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0
[00:01:00.193,969] <err> os: Fault during interrupt handling

[00:01:00.194,000] <err> os: Current thread: 0x200066a8 (unknown)
[00:01:00.465,148] <err> fatal_error: Resetting system
*** Booting Zephyr OS build v3.1.99-ncs1 ***

Debug:

Device tree:

&i2c1 {
	compatible = "nordic,nrf-twim";
	status = "okay";
	clock-frequency = <I2C_BITRATE_FAST>;
	pinctrl-0 = <&i2c1_default>;
	pinctrl-1 = <&i2c1_sleep>;
	pinctrl-names = "default", "sleep";

	touch_controller: ft5336@38 {
		compatible = "focaltech,ft5336";
		reg = <0x38>;
		label = "FT5336";
		int-gpios = <&gpio1 11 GPIO_ACTIVE_HIGH>; // YD
	};
};

I'm suspicious of the issue being related to my kscan callback because:

It is the only interrupt off of I2C
Commenting out registration of the callback avoids the error

I've read similar posts that say this issue arises when an interrupt interrupts an interrupt - Am I understanding that correctly? If so, shouldn't interrupt priorities avoid this? Where/how is this managed? Also worth noting this application uses bluetooth soft device, timers (rtc2), uart, pwm, etc.

Other info:

Zephyr: 3.1.99-ncs1

nRF Connect SDK: 2.1.0

nRF Connect for Desktop: 3.12.0

Development Platform: Windows

Board: Custom

Edit:
Not sure if it's related by occasionally see "<err> i2c_nrfx_twim: Error on I2C line occurred for message 0" in my application at roughly the same frequency, although I do not see this at the same time as the CPU fault.

Håkon Alseth · Accepted Answer

Hi,

Application is communicating with a touch controller (FT5336) over I2C and registering a callback with kscan_config() and kscan_enable_callback(). Every few minutes a "ZEPHYR FATAL ERROR 0: CPU exception on CPU 0" (Fault during interrupt handling) occurs, restarting the application. Using debug I can see two "<signal handler called>" (photo'd) and I always see a call to "i2c_dump_msgs()" as the lowest call.

The functions you're calling are effectively these, as you're selecting the FT5336 device:

https://github.com/nrfconnect/sdk-zephyr/blob/v3.2.99-ncs2/drivers/kscan/kscan_ft5336.c#L223-L225

I would recommend that you first adjust your CONFIG_MAIN_STACK_SIZE to a higher value, for instance 4096.

If you still see assertions, you should scope your SDA/SCL pins using a logic analyzer to see if the communication is working towards your sensor.

Not sure if it's related by occasionally see "<err> i2c_nrfx_twim: Error on I2C line occurred for message 0" in my application at roughly the same frequency, although I do not see this at the same time as the CPU fault.

This normally means that it has problems communicating on that specific address:

https://github.com/nrfconnect/sdk-zephyr/blob/v3.2.99-ncs2/drivers/i2c/i2c_nrfx_twi.c#L131

I've read similar posts that say this issue arises when an interrupt interrupts an interrupt - Am I understanding that correctly? If so, shouldn't interrupt priorities avoid this? Where/how is this managed? Also worth noting this application uses bluetooth soft device, timers (rtc2), uart, pwm, etc.

Are you experiencing the same problems if you isolate the functionality towards this specific sensor?

Kind regards,

Håkon

Kscan callback triggers fault during interrupt handling

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