topic Re: imx8m reset without WDOG_B signal usage in i.MX Processors

imx8m reset without WDOG_B signal usage

wolfgang_baer — Thu, 08 Aug 2019 15:05:54 GMT

Hi,

i have a problem with the watchdog operation on our custom imx8m board.

Our board does NOT use the WDOG_B signal for PMIC reset and we are not able to change this.

Resetting the board in u-boot works like given in the reference manual:
Setting the 0x3028000 register to e.g. 0x14 resets the SOC and I get also watchdog timeout as the source of the reset in the status register. Also asserting the SRS bit resets the SOC and gives the correct reset source in the status register.

After booting Linux this no longer works - after forcing a watchdog timeout the SOC just freezes.

The voltage sources are as required for SOC startup so this should not be a problem. We boot from EMMC and the RST

pin is connected.

Any hints what else I can check or anyone with same setup (no WDOG_B signal to PMIC)?

Regards,

Wolfgang

Re: imx8m reset without WDOG_B signal usage

Yuri — Fri, 09 Aug 2019 05:27:56 GMT

Hello,

It is recommended to remove power (voltage) to all components on the board,

even in case a processor reset, since some external devices, such as eMMC, SD,

QSPI, DDR) may stay in non predictable state; as result system boot does not work.

In Your case, I think, memory is the reason. Perhaps it is necessary to issue

PreCharge All command at the beginning of the LPDDR initialization and to reset

the READ FIFO Pointers.

Have a great day,
Yuri

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.

Re: imx8m reset without WDOG_B signal usage

wolfgang_baer — Fri, 09 Aug 2019 06:05:19 GMT

Hi Yuri,

thanks for your fast response. I know it is recommended to remove power but as said this no option for us currently.

Regarding memory. Do you mean to perform the mentioned commands in the LPDDR4 initialization code in SPL?
Do you have any hints about documentation of these commands as I am currently just using the DDR Tool generated
initialization code in the SPL DDR initialization.

Do you also have a clue why it does work in u-boot (at command prompt) but not after loading of Linux?
What could be the difference here regarding memory?

Thanks, your help is really appreciated,

Wolfgang

Re: imx8m reset without WDOG_B signal usage

Yuri — Fri, 09 Aug 2019 06:40:53 GMT

Hello,

Is it possible to run simple memory test of U-boot - in order to exclude memory issue?

Regards,

Yuri.

Re: imx8m reset without WDOG_B signal usage

wolfgang_baer — Fri, 09 Aug 2019 07:01:38 GMT

Hi Yuri,

a simple mtest in u-boot for the memory shows no errors.

Also the DDR-Tool stress-tests done during board bring up showed now errors.

Do you have a hint regarding documentation / changes for the memory commands you mentioned in your first post?

Thanks,

Wolfgang

Re: imx8m reset without WDOG_B signal usage

Yuri — Mon, 12 Aug 2019 13:12:20 GMT

Hello,

Since for i.MX8M the SPL contains the codes for DDR PHY and DDR controller initialization
and DDR PHY training, usually it is recommended to use the recent firmware from the the DDR Tool;

it should provide all the required initialization.

Also, it makes sense to get the Stress test working.

https://community.nxp.com/docs/DOC-340179

Regards,

Yuri.

Re: imx8m reset without WDOG_B signal usage

wolfgang_baer — Mon, 12 Aug 2019 13:19:14 GMT

Hi Yuri,

yes, we are using the latest Version of the DDR Tool (V2.10) with the latest Excel sheet for LPDDR4 (v23).

The stress test works on our board without issues.

The same effect I can also see on the EVK board if I disable the WDOG_B assert functionality:

- Watchdog works on the u-boot prompt -> it resets the device

- After booting to linux prompt -> the same watchdog call does just stall/freeze the device

Regards,

Wolfgang

Re: imx8m reset without WDOG_B signal usage

Yuri — Mon, 19 Aug 2019 07:45:56 GMT

Hello,

Let me look at the schematic. I will create request for it.

Regards,

Yuri.

Re: imx8m reset without WDOG_B signal usage

reyhanehyazdani — Thu, 17 Oct 2019 11:44:57 GMT

Hi Wolfgang,

I also have the same problem. Did you find any answer for that?

Regards,

Reyhaneh

Re: imx8m reset without WDOG_B signal usage

wolfgang_baer — Mon, 21 Oct 2019 07:40:42 GMT

Hi Reyhaneh,

I am sorry – no. I have not managed to get a solution regarding this issue.

Basically NXP states to reset the PMIC – however this is a no go for us too.

If we found a solution I will report it here.

Regards,

Wolfgang

Re: imx8m reset without WDOG_B signal usage

emptyfridge — Tue, 15 Dec 2020 13:31:57 GMT

Hi guys,

Try to get out SRSR Reset Status Register (0x3039005c). Well it works, but it looks like it never changes status. No matter how I boot/reboot/reset/poweroffon/wdog/ the i.mx8mm src_reg srsr is every time 0x01.

Is there a known issue, that it is not working properly?

Or am I doing something wrong?

u-boot-imx_2019.04

u32 get_imx_reset_cause(void)
{
struct src *src_regs = (struct src *)SRC_BASE_ADDR;

if (reset_cause == -1) {
printf("0 src_regs %.8x \n", src_regs);
printf("0 src_regs %.8x \n", &src_regs);
printf("0 src_regs->srsr %.8x \n", src_regs->srsr);
printf("0 src_regs->srsr %.8x \n", &src_regs->srsr);
reset_cause = readl(&src_regs->srsr);
printf("1 reset cause %.8x \n", reset_cause);
/* preserve the value for U-Boot proper */
#if !defined(CONFIG_SPL_BUILD) && !defined(CONFIG_ANDROID_BOOT_IMAGE)
/* We will read the ssrs states later for android so we don't
* clear the states here.
*/
writel(reset_cause, &src_regs->srsr);
printf(" 2 write reset cause %.8x \n", &src_regs->srsr);
printf(" 2 read reset cause %.8x \n", src_regs->srsr);
#endif
writel(reset_cause, &src_regs->srsr);
printf(" 3 2write reset cause %.8x \n", &src_regs->srsr);
printf(" 3read reset cause %.8x \n", src_regs->srsr);
}

return reset_cause;
}

thanks for your help.

Re: imx8m reset without WDOG_B signal usage

cedric_starke — Wed, 23 Dec 2020 08:06:44 GMT

Hello @wolfgang_baer ,

I know, the issue is not really new, but we have the same problem with our imx8m mini and I just want to ask for your solution of this problem?

We additionally figured out that this just happens with the imx8m mini. We use the same PCB for the imx8m nano and this SOC is able to reboot correctly.

So, if you can share your last state with us we would be grateful.

Best regards

Cedric

Re: imx8m reset without WDOG_B signal usage

wolfgang_baer — Tue, 29 Dec 2020 18:25:25 GMT

Hi Cedric,

we did not found/search for a solution but connected the WDOG_B pin via a 100k PU to the
SOC reset pin (POR_B) in the next redesign. This way we can reset the SOC by
watchdog without touching the PMIC.

Regards,

Wolfgang

Re: imx8m reset without WDOG_B signal usage

cedric_starke — Wed, 13 Jan 2021 14:42:30 GMT

Hi Wolfgang,

thanks for your answer. That's the same way we use to get the reboot work. Luckily we already intended this in the PCB layout with a unequipped bridge. In the next version we will insert this bridge.

But in my opinion it is a software issue of the imx8m mini package. Because uboot can do the reset without the POR_B signal and the imx8m nano also in uboot AND linux.

We tested this with the 4.14.98 and 5.4.47 version. In both the same "problem". This just as information for anybody else who reads this thread.

If anybody finds the software bug feel free to post her, because we are still interested in the correct solution.

Best regards

Cedric

Re: imx8m reset without WDOG_B signal usage

siva_prabhakara — Fri, 18 Jun 2021 16:42:22 GMT

@cedric_starke i also bumped to the same issue on imx8mm(5.4 kernel), were you or anyone able to identify the software issue here?

Re: imx8m reset without WDOG_B signal usage

cedric_starke — Mon, 21 Jun 2021 04:54:59 GMT

Hi Siva,

just like with Wolfgang. After we "fixed", or let me say optimized, the hardware we didn't investigate any more time to this issue. We still use the kernel 5.4.47. Meanwhile a newer version is available. Maybe there is a fix included. But honestly, I wouldn't expect it.

If you find any software fix the solution is still interesting.

Best regards

Cedric

Re: imx8m reset without WDOG_B signal usage

DefieldsJ — Tue, 11 Jan 2022 16:06:18 GMT

Hi, I'm having the same issue on a custom imx8mm-based board. Uboot 'reset' command works as expected, but linux 'reboot' command hangs without any specific error output.

Has anyone figured out how to work around this issue without hardware modifications?

Thanks in advance,

Justin D.

Re: imx8m reset without WDOG_B signal usage

DefieldsJ — Wed, 12 Jan 2022 14:39:25 GMT

@siva_prabhakara Did you ever find a firmware solution to the issue?

Re: imx8m reset without WDOG_B signal usage

timharvey — Tue, 14 Nov 2023 19:56:23 GMT

I recently ran into this and found it related to PSCI cpu-idle. If you disable CONFIG_ARM_PSCI_CPUIDLE, or boot with cpuidle.off=1 which disables cpuidle in general I found the system warm resetting as expected. I'm not sure what causes this however.

Re: imx8m reset without WDOG_B signal usage

driftdjindustries — Sun, 15 Feb 2026 13:55:24 GMT

Adding this reply because I managed to fix the same issue via software:

Custom board w/IMX8MN + PCA9450
Custom Linux distro using KConfig
Reset cmd works in U-Boot
Any Linux watchdog command (reboot, etc.) hangs but doesn't reset the system
GPIO2 (WDOG-B) pin doesn't respond to Linux watchdog commands

In my case, there were 2 problems:

I didn't have the correct WDT driver enabled in KConfig (CONFIG_IMX2_WDT/imx2_wdt.c). So the kernel wasn't able to correctly process the watchdog commands.
The PCA9450 driver in the mainline kernel (pca9450-regulator.c) doesn't correctly handle the reset control register options - specifically there's no way to do a full cold-reset. My design requires the PCA9450 to cycle power in all domains, but the driver won't cycle power to the LDO1/2 domains, even during a reset. The PCA6450 data sheet provides an option for cycling power in all domains, it's just not handled in the mainline kernel driver. Here's a code snippet taken from the probe function:

if (of_property_read_bool(i2c->dev.of_node, "nxp,wdog_b-warm-reset")) reset_ctrl = WDOG_B_CFG_WARM; else reset_ctrl = WDOG_B_CFG_COLD_LDO12;

There's an option missing for "WDOG_B_CFG_COLD." In my case, I just hardcoded it into my own version of the driver and dumped it into the compile tree manually. It's super-hacky but it worked as a proof-of-concept. Not sure if there's anyone out there with a Kernel Maintainer's ear, but I'm just a front-end guy...

tl;dr:

1) Ensure you are compiling the correct WDT driver in the kernel, and 2) if you're using the PCA9450 PMIC, check the regulator driver to make sure it's giving you the full cold-reset flow.

Hope that helps someone!