LIS2DU12 wake up configuration

[Ch4rly]

Hi everyone,

I'm using 2 LIS2DU12 on one object.

The first one is configured in continuous mode. I forward the samples directly to a computer. I use it to check the wake up triggering configuration of the second one.

The second one is configured in continuous-to-FIFO mode. And I'm trying to get it to wake up when the acceleration on one axis is over 2g for at least 8.75ms. ODR is 800Hz, FS=16g, so I set :

WK_THS=8
WAKE_THS_W=0
=> threshold = 2g x 2⁶ / 16g = 8

WAKE_DUR=01 (7 ODR_time)
WU_DUR_X4=1
=> Wake-up duration = 7 / 800 = 8.75ms

The first LIS2DU12 configured in continuous mode shows that during my tests I get 4g for over 20ms, yet the second LIS2DU12 does not wake up. But if I set the threshold to 4 (i.e. 1g according to my calculations) it does wake up, and I recover 2 very similar acquisitions.

What did I misunderstand ?

Here is a code snippet of the configuration of the LIS2DU12 in continuous-to-FIFO mode:

  lis2du12_pin_int_route_t int_route;
  lis2du12_status_t status;
  lis2du12_id_t id;

  /* Initialize mems driver interface */
  dev_ctx.write_reg = spi_write;
  dev_ctx.read_reg = spi_read;
  dev_ctx.mdelay = platform_delay;
  dev_ctx.handle = p_bus;

  /* Wait sensor boot time */
  platform_delay(BOOT_TIME);

  /* Check device ID */
  lis2du12_id_get(&dev_ctx, &id);
  if (id.whoami == LIS2DU12_ID)
  {
    printf("-Part ID: 0x%02X\r\n", id.whoami);
  }
  else
  {
    printf("Echec Lecture ID...\r\n");
  }

  /* Restore default configuration */
  lis2du12_init_set(&dev_ctx, LIS2DU12_RESET);
  do {
  lis2du12_status_get(&dev_ctx, &status);
  } while (status.sw_reset);


  /* Set bdu and if_inc recommended for driver usage */
  lis2du12_init_set(&dev_ctx, LIS2DU12_DRV_RDY);


  // Configure CTRL 5 en power down
  md.odr = LIS2DU12_OFF;
  lis2du12_mode_set(&dev_ctx, &md);

  // configure mode Wake up
  // Activer la détection sur X, Y et Z
  wkup_md.x_en = 1;
  wkup_md.y_en = 1;
  wkup_md.z_en = 1;
  wkup_md.threshold = 8; // Thres=±2g, FS=±16g, 1LSB of thres=FS/2^6 => 2g*2⁶/16g=2³
  wkup_md.duration  = 5; // 5 => WU_DUR_X4=1 & WAKE_DUR=1 => duration=7 ODR_time =7/800Hz=8,75ms
  wkup_md.sleep.en = 0;
  lis2du12_wake_up_mode_set(&dev_ctx,&wkup_md);


  /* Select bus interface */
  lis2du12_bus_mode_set(&dev_ctx, LIS2DU12_I3C_DISABLE);

  /* Set FIFO watermark to 64 sample(s) */
  fifo_mode.store = LIS2DU12_8_BIT;
  fifo_mode.watermark = 64;
  fifo_mode.operation = LIS2DU12_STREAM_TO_FIFO;
  lis2du12_fifo_mode_set(&dev_ctx, &fifo_mode);


  // CONFIGURE CTRL 5 en 16g et ODR de 800Hz
  /* Set Output Data Rate */
  md.fs =  LIS2DU12_16g;
  md.odr = LIS2DU12_800Hz;
  lis2du12_mode_set(&dev_ctx, &md);


  /* Configure interrupt pins */
  lis2du12_pin_int2_route_get(&dev_ctx, &int_route);
  int_route.wake_up = PROPERTY_ENABLE;
  lis2du12_pin_int2_route_set(&dev_ctx, &int_route);

[Federica Bossi]

Hi @Ch4rly ,

Some suggestions:

• Try setting wkup_md.duration = 1; to have 7 ODR cycles duration with WU_DUR_X4=1.
• Explicitly set the WU_DUR_X4 bit: if the driver does not set it automatically, write directly to the MD1_CFG (0x1F) register bit 4 (WU_DUR_X4).

Hope this helps!

[Ch4rly]

Hi Federica,

Thanks for the reply.

I checked that's what "lis2du12_wake_up_mode_set" does : WU_DUR_X4=1 and WAKE_DUR=01.

Does my calculations make sense to you ?

[Ch4rly]

Hi @Federica Bossi,

Thanks for the reply.

I checked that's what "lis2du12_wake_up_mode_set" does : WU_DUR_X4=1 and WAKE_DUR=01.

That being said. Does my calculations for

• threshold=2G
• wake-up duration=8.75ms

make sense to you ?

[Federica Bossi]

Hi @Ch4rly ,

Your calculations are ok. Please consider that wake-up function use slope filtered data (see AN5648 5.1), and threshold apply to output of internally filtered data. Also consider that Cont-to-FIFO mode can be triggered if wake-up interrupt is routed to INT1 pin (AN5648 6.4.4), which I cannot see in your code.

[Ch4rly]

Hi Federica,
Thank you for your reply. Can you please clarify again the following points ?

"Wake-up function use slope filtered data ... and threshold apply to output of internally filtered data."
Wake-up function is controlled by a threshold (WK_THS, WAKE_THS_W) and a duration (WAKE_DUR, WU_DUR_X4). In the second part of your sentence which threshold are you talking about ?

From AN5648 §3.1.1, the "accelerometer slope" is the derivation of the acceleration (slope(t n ) = [ acc(t n ) - acc(t n-1 ) ] / 2).
Therefore the WK_THS should have a unit consistent with g/s or m/s³, no ?
Is there any way to wake up on an acceleration instead of its derivation ?

I did a capture and I worked on the data in a spreadsheet (see in attachment the file acc_and_slope_curves.ods).
In this file, if the "slop" had stayed over 2 (WK_THS) for over 8.75ms (WAKE_DUR), wake-up function would have been triggered, am I right ?

"Cont-to-FIFO mode can be triggered if wake-up interrupt is routed to INT1 pin ... which I cannot see in your code."
We use INT2, is this the code you were looking for?

/* Configure interrupt pins */
lis2du12_pin_int2_route_get(&dev_ctx, &int_route);
int_route.wake_up = PROPERTY_ENABLE;
lis2du12_pin_int2_route_set(&dev_ctx, &int_route);