BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

lcj — Wed, 13 Aug 2025 11:19:03 GMT

That didn't work. Seems to keep restarting over and over again when trying to switch between 1V8 and 3V0.

I've tried with all kinds of variations of wait time between the vregh call (which does nothing the 2nd time btw, so it should not be a problem) and the accelerometer initialization, even so much as 1 minute.

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

lcj — Tue, 29 Jul 2025 13:35:06 GMT

Ok. All of that is way over my head. It seems like there should be a way to control the timing of initialization. I guess checking with the code you provided will prove if the theory you have is correct or not. It seems like changing the VREGH every time is a little extreme, but I can test it out.

There is no UICR_VREGHVOUT_VREGHVOUT_0V0

These are the options:

/* Bits 2..0 : VREGH regulator output voltage. */
#define UICR_VREGHVOUT_VREGHVOUT_Pos (0UL) /*!< Position of VREGHVOUT field. */
#define UICR_VREGHVOUT_VREGHVOUT_Msk (0x7UL << UICR_VREGHVOUT_VREGHVOUT_Pos) /*!< Bit mask of VREGHVOUT field. */
#define UICR_VREGHVOUT_VREGHVOUT_1V8 (0x0UL) /*!< 1.8 V */
#define UICR_VREGHVOUT_VREGHVOUT_2V1 (0x1UL) /*!< 2.1 V */
#define UICR_VREGHVOUT_VREGHVOUT_2V4 (0x2UL) /*!< 2.4 V */
#define UICR_VREGHVOUT_VREGHVOUT_2V7 (0x3UL) /*!< 2.7 V */
#define UICR_VREGHVOUT_VREGHVOUT_3V0 (0x4UL) /*!< 3.0 V */
#define UICR_VREGHVOUT_VREGHVOUT_3V3 (0x5UL) /*!< 3.3 V */
#define UICR_VREGHVOUT_VREGHVOUT_DEFAULT (0x7UL) /*!< Default voltage: 1.8 V */

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

Susheel Nuguru — Tue, 29 Jul 2025 12:15:47 GMT

because somehow debugger is changing the timings of the initialization inserting delays which happen to luckily working in the right way to stretch out time between rail goes to 3v and the driver probing the chip.

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

lcj — Tue, 29 Jul 2025 10:48:46 GMT

But why does it work when I step through the debugger using my segger after it has already been set to 3V?

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

alicejess889 — Tue, 29 Jul 2025 07:58:38 GMT

It makes perfect sense that if the power manager only actively switches the rail when there's a change in voltage, then simply requesting the same 3V it's already providing wouldn't trigger a true "power-on" cycle for the BMI270. The sensor melon sandbox effectively never sees that fresh power transition it needs for a proper reset and initialization.

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

Susheel Nuguru — Tue, 29 Jul 2025 07:34:49 GMT

I think what is happening is that this little “power manager” only actually switches the rail when it goes from one voltage to another. The very first time you ask it to turn on 3 V, it does the job. But after that, asking for 3 V again does nothing because it’s already sitting at 3 V, even though the BMI270 never saw that fresh power-on. So when you stick a k_sleep() right inside bmi270_init(), it works. By then you’ve effectively powered the sensor and given it time to wake up. But your SYS_INIT(..., POST_KERNEL) trick didn’t help, because you had already set the rail to 3 V and never toggled it a second time before the driver started.

Easy workaround is to pulse the rail off and on again in the very early stages of SYS_INIT so that every boot actually transitions power.

Do something like this

static int set_voltage_early(const struct device *unused)
{
    ARG_UNUSED(unused);

    LOG_DBG("Power-cycling BMI270 rail");
    change_gpio_voltage(UICR_VREGHVOUT_VREGHVOUT_0V0);
    k_sleep(K_MSEC(5));

    change_gpio_voltage(UICR_VREGHVOUT_VREGHVOUT_3V0);
    k_sleep(K_MSEC(10));

    return 0;
}
SYS_INIT(set_voltage_early, PRE_KERNEL_1, 0);

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

lcj — Fri, 25 Jul 2025 10:57:09 GMT

No luck:

00> [00:00:00.740,661] <err> voltage: setup: -134
00> *** Booting nRF Connect SDK v2.9.1-60d0d6c8d42d ***
00> *** Using Zephyr OS v3.7.99-ca954a6216c9 ***
00> [00:00:00.741,485] <dbg> app: main: Starting BMI270 sensor example, test number 1
00> [00:00:00.741,516] <inf> voltage_mgr: change_gpio_voltage: REGOUT = 0xfffffffc
00> [00:00:00.741,516] <inf> voltage_mgr: change_gpio_voltage: target voltage is 4
00> [00:00:00.741,516] <dbg> app: main: Waiting 60 seconds for voltage to stabilize
00> [00:01:00.741,638] <err> app: Device bmi270@68 is not ready

and:

00> [00:00:00.742,095] <err> voltage: setup: -134
00> *** Booting nRF Connect SDK v2.9.1-60d0d6c8d42d ***
00> *** Using Zephyr OS v3.7.99-ca954a6216c9 ***
00> [00:00:00.742,919] <dbg> app: main: Starting BMI270 sensor example, test number 1
00> [00:00:00.742,950] <inf> voltage_mgr: change_gpio_voltage: REGOUT = 0xfffffffc
00> [00:00:00.742,950] <inf> voltage_mgr: change_gpio_voltage: target voltage is 4
00> [00:00:00.742,950] <dbg> app: main: Waiting 120 seconds for voltage to stabilize
00> [00:02:00.743,072] <err> app: Device bmi270@68 is not ready

and:

00> [00:00:00.733,551] <err> voltage: setup: -134
00> *** Booting nRF Connect SDK v2.9.1-60d0d6c8d42d ***
00> *** Using Zephyr OS v3.7.99-ca954a6216c9 ***
00> [00:00:00.734,375] <dbg> app: main: Starting BMI270 sensor example, test number 1
00> [00:00:00.734,405] <inf> voltage_mgr: change_gpio_voltage: REGOUT = 0xfffffffc
00> [00:00:00.734,405] <inf> voltage_mgr: change_gpio_voltage: target voltage is 4
00> [00:00:00.734,405] <dbg> app: main: Waiting 300 seconds for voltage to stabilize
00> [00:05:00.734,527] <err> app: Device bmi270@68 is not ready

change_gpio_voltage only does it the first time if it's not at the right setting.

However when I put k_sleep(K_SECONDS(2)); in it works:

static int bmi270_init(const struct device *dev)
{
	int ret;
	struct bmi270_data *data = dev->data;
	uint8_t chip_id;
	uint8_t soft_reset_cmd;
	uint8_t init_ctrl;
	uint8_t msg;
	uint8_t tries;
	uint8_t adv_pwr_save;
k_sleep(K_SECONDS(2));
	ret = bmi270_bus_check(dev);
	if (ret < 0) {
		LOG_ERR("Could not initialize bus");
		return ret;
	}
	
	...
}

Obviously, that's not a solution, but I hope it helps determine the problem and solution. Is there any way to delay the init?

I've even tried this:

static int set_volttage_early(void)
{
	int sleep_time = 2; // seconds
	LOG_DBG("Setting GPIO voltage early in boot process");
    int rt = change_gpio_voltage(UICR_VREGHVOUT_VREGHVOUT_3V0);
	LOG_DBG("sleeping for %d seconds", sleep_time);
	k_sleep(K_SECONDS(sleep_time));
	return rt;
}

SYS_INIT(set_volttage_early, POST_KERNEL, 1);

But it doesn't work (I put debug statements in the init to show order):

00> [00:00:00.719,299] <dbg> app: set_volttage_early: Setting GPIO voltage early in boot process
00> [00:00:00.719,299] <inf> voltage_mgr: change_gpio_voltage: REGOUT = 0xfffffffc
00> [00:00:00.719,329] <inf> voltage_mgr: change_gpio_voltage: target voltage is 4
00> [00:00:00.719,329] <inf> voltage_mgr: Target voltage already set. No action needed.
00> [00:00:00.719,329] <dbg> app: set_volttage_early: sleeping for 2 seconds
00> [00:00:02.719,696] <err> voltage: setup: -134
00> [00:00:02.719,726] <dbg> bmi270: bmi270_init: Initializing BMI270 sensor
00> *** Booting nRF Connect SDK v2.9.1-60d0d6c8d42d ***
00> *** Using Zephyr OS v3.7.99-ca954a6216c9 ***
00> [00:00:02.720,520] <dbg> app: main: Starting BMI270 sensor example, test number 2
00> [00:00:02.720,550] <dbg> app: main: Waiting 1 seconds for voltage to stabilize
00> [00:00:03.720,642] <err> app: Device bmi270@68 is not ready

Seems strange I can delay before the init, but it only works in the init.

RE: BMI270 Accelerometer device is ready when debugging but not when just flashing on a custom board

Susheel Nuguru — Thu, 24 Jul 2025 08:43:34 GMT

It seems to me that the issue on your custom board the BMI270 driver runs immediately after reset, but the new 3 V rail isn’t stable yet. In a debugger session the halt gives enough time for the LDO to settle, but in a normal boot the sensor probe races ahead and fails.

Can you try to add some delay about 50msafter change_gpio_voltage and before DEVICE_DT_GET_ONE so that it can give the sensor some time to initialize. It is very possible that the debugger which inserts extra clock cycles to halt the PC for debugging inserts enough delay to let the sensor initialize properly. Please try and let me know if this works.